UICollectionView 类:
Inherits from | |
Conforms to | |
Framework |
/System/Library/Frameworks/UIKit.framework
|
Availability |
Available in iOS 6.0 and later.
|
Declared in |
UICollectionView.h
|
Related sample code |
Overview(概览)
The UICollectionView
class manages an ordered collection of data items and presents them using customizable layouts. Collection views provide the same general function as table views except that a collection view is able to support more than just single-column layouts. Collection views support customizable layouts that can be used to implement multi-column grids, tiled layouts, circular layouts, and many more. You can even change the layout of a collection view dynamically if you want.
When adding a collection view to your user interface, your app’s main job is to manage the data associated with that collection view. The collection view gets its data from the data source object, which is an object that conforms to theUICollectionViewDataSource
protocol and is provided by your app. Data in the collection view is organized into individual items, which can then be grouped into sections for presentation. An item is the smallest unit of data you want to present. For example, in a photos app, an item might be a single image. The collection view presents items onscreen using a cell, which is an instance of the UICollectionViewCell
class that your data source configures and provides.
In addition to its cells, a collection view can present data using other types of views too. These supplementary views can be things like section headers and footers that are separate from the individual cells but still convey some sort of information. Support for supplementary views is optional and defined by the collection view’s layout object, which is also responsible for defining the placement of those views.
Besides embedding it in your user interface, you use the methods of UICollectionView
object to ensure that the visual presentation of items matches the order in your data source object. Thus, whenever you add, delete, or rearrange data in your collection, you use the methods of this class to insert, delete, and rearrange the corresponding cells. You also use the collection view object to manage the selected items, although for this behavior the collection view works with its associated delegate
object.
Collection Views and Layout Objects
A very important object associated with a collection view is the layout object, which is a subclass of theUICollectionViewLayout
class. The layout object is responsible for defining the organization and location of all cells and supplementary views inside the collection view. Although it defines their locations, the layout object does not actually apply that information to the corresponding views. Because the creation of cells and supplementary views involves coordination between the collection view and your data source object, the collection view actually applies layout information to the views. Thus, in a sense, the layout object is like another data source, only providing visual information instead of item data.
You normally specify a layout object when creating a collection view but you can also change the layout of a collection view dynamically. The layout object is stored in the collectionViewLayout
property. Setting this property directly updates the layout immediately, without animating the changes. If you want to animate the changes, you must call thesetCollectionViewLayout:animated:
method instead.
Creating Cells and Supplementary Views
The collection view’s data source object provides both the content for items and the views used to present that content. When the collection view first loads its content, it asks its data source to provide a view for each visible item. To simplify the creation process for your code, the collection view requires that you always dequeue views, rather than create them explicitly in your code. There are two methods for dequeueing views. The one you use depends on which type of view has been requested:
Use the
dequeueReusableCellWithReuseIdentifier:forIndexPath:
to get a cell for an item in the collection view.Use the
dequeueReusableSupplementaryViewOfKind:withReuseIdentifier:forIndexPath:
method to get a supplementary view requested by the layout object.
Before you call either of these methods, you must tell the collection view how to create the corresponding view if one does not already exist. For this, you must register either a class or a nib file with the collection view. For example, when registering cells, you use the registerClass:forCellWithReuseIdentifier:
orregisterNib:forCellWithReuseIdentifier:
method. As part of the registration process, you specify the reuse identifier that identifies the purpose of the view. This is the same string you use when dequeueing the view later.
After dequeueing the appropriate view in your delegate method, configure its content and return it to the collection view for use. After getting the layout information from the layout object, the collection view applies it to the view and displays it.
For more information about implementing the data source methods to create and configure views, seeUICollectionViewDataSource Protocol Reference.
Tasks
Initializing a Collection View
Configuring the Collection View
-
collectionViewLayout
property – setCollectionViewLayout:animated:
-
delegate
property -
dataSource
property -
backgroundView
property
Creating Collection View Cells
– registerClass:forCellWithReuseIdentifier:
– registerNib:forCellWithReuseIdentifier:
– registerClass:forSupplementaryViewOfKind:withReuseIdentifier:
– registerNib:forSupplementaryViewOfKind:withReuseIdentifier:
– dequeueReusableCellWithReuseIdentifier:forIndexPath:
– dequeueReusableSupplementaryViewOfKind:withReuseIdentifier:forIndexPath:
Reloading Content
Getting the State of the Collection View
Inserting, Moving, and Deleting Items
Inserting, Moving, and Deleting Sections
Managing the Selection
-
allowsSelection
property -
allowsMultipleSelection
property – indexPathsForSelectedItems
– selectItemAtIndexPath:animated:scrollPosition:
– deselectItemAtIndexPath:animated:
Locating Items in the Collection View
– indexPathForItemAtPoint:
– indexPathsForVisibleItems
– indexPathForCell:
– cellForItemAtIndexPath:
Getting Layout Information
Scrolling an Item Into View
Animating Multiple Changes to the Collection View
Properties
allowsMultipleSelection
A Boolean value that determines whether users can select more than one item in the collection view.
Discussion
This property controls whether multiple items can be selected simultaneously. The default value of this property is NO
.
When the value of this property is YES
, tapping a cell adds it to the current selection (assuming the delegate permits the cell to be selected). Tapping the cell again removes it from the selection.
Availability
- Available in iOS 6.0 and later.
See Also
Declared In
UICollectionView.h
allowsSelection
A Boolean value that indicates whether users can select items in the collection view.
Discussion
If the value of this property is YES
(the default), users can select items. If you want more fine-grained control over the selection of items, you must provide a delegate object and implement the appropriate methods of theUICollectionViewDelegate
protocol.
Availability
- Available in iOS 6.0 and later.
See Also
Declared In
UICollectionView.h
backgroundView
The view that provides the background appearance.
Discussion
The view (if any) in this property is positioned underneath all of the other content and sized automatically to fill the entire bounds of the collection view. The background view does not scroll with the collection view’s other content. The collection view maintains a strong reference to the background view object.
This property is nil
by default, which displays the background color of the collection view.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
collectionViewLayout
The layout used to organize the collected view’s items.
Discussion
Assigning a new layout object to this property causes the new layout to be applied (without animations) to the collection view’s items.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
dataSource
The object that provides the data for the collection view.
Discussion
The data source must adopt the UICollectionViewDataSource
protocol. The collection view maintains a weak reference to the data source object.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
delegate
The object that acts as the delegate of the collection view.
Discussion
The delegate must adopt the UICollectionViewDelegate
protocol. The collection view maintains a weak reference to the delegate object.
The delegate object is responsible for managing selection behavior and interactions with individual items.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
Instance Methods
cellForItemAtIndexPath:
Returns the cell object at the specified index path.
Parameters
- indexPath
-
The index path that specifies the section and item number of the cell.
Return Value
The cell object at the corresponding index path or nil
if no cell was found at that location.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
deleteItemsAtIndexPaths:
Deletes the items at the specified index paths.
Parameters
- indexPaths
-
An array of
NSIndexPath
objects, each of which contains a section index and item index for the item you want to delete from the collection view. This parameter must not benil
.
Discussion
Use this method to remove items from the collection view. You might do this when you remove the items from your data source object or in response to user interactions with the collection view. The collection view updates the layout of the remaining items to account for the deletions, animating the remaining items into position as needed.
You can also call this method from a block passed to the performBatchUpdates:completion:
method when you want to animate multiple separate changes into place at the same time. See the description of that method for more information.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
deleteSections:
Deletes the sections at the specified indexes.
Parameters
- sections
-
The indexes of the sections you want to delete. This parameter must not be
nil
.
Discussion
Use this method to remove the sections and their items from the collection view. You might do this when you remove the sections from your data source object or in response to user interactions with the collection view. The collection view updates the layout of the remaining sections and items to account for the deletions, animating the remaining items into position as needed.
You can also call this method from a block passed to the performBatchUpdates:completion:
method when you want to animate multiple separate changes into place at the same time. See the description of that method for more information.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
dequeueReusableCellWithReuseIdentifier:forIndexPath:
Returns a reusable cell object located by its identifier
Parameters
- identifier
-
The reuse identifier for the specified cell. This parameter must not be
nil
. - indexPath
-
The index path specifying the location of the cell. The data source receives this information when it is asked for the cell and should just pass it along. This method uses the index path to perform additional configuration based on the cell’s position in the collection view.
Return Value
A valid UICollectionReusableView
object.
Discussion
Call this method from your data source object when asked to provide a new cell for the collection view. This method dequeues an existing cell if one is available or creates a new one based on the class or nib file you previously registered.
Important: You must register a class or nib file using the registerClass:forCellWithReuseIdentifier:
orregisterNib:forCellWithReuseIdentifier:
method before calling this method.
If you registered a class for the specified identifier and a new cell must be created, this method initializes the cell by calling its initWithFrame:
method. For nib-based cells, this method loads the cell object from the provided nib file. If an existing cell was available for reuse, this method calls the cell’s prepareForReuse
method instead.
Availability
- Available in iOS 6.0 and later.
Related Sample Code
Declared In
UICollectionView.h
dequeueReusableSupplementaryViewOfKind:withReuseIdentifier:forIndexPath:
Returns a reusable supplementary view located by its identifier and kind.
Parameters
- elementKind
-
The kind of supplementary view to retrieve. This value is defined by the layout object. This parameter must not be
nil
. - identifier
-
The reuse identifier for the specified view. This parameter must not be
nil
. - indexPath
-
The index path specifying the location of the supplementary view in the collection view. The data source receives this information when it is asked for the view and should just pass it along. This method uses the information to perform additional configuration based on the view’s position in the collection view.
Return Value
A valid UICollectionReusableView
object.
Discussion
Call this method from your data source object when asked to provide a new supplementary view for the collection view. This method dequeues an existing view if one is available or creates a new one based on the class or nib file you previously registered.
Important: You must register a class or nib file using theregisterClass:forSupplementaryViewOfKind:withReuseIdentifier:
orregisterNib:forSupplementaryViewOfKind:withReuseIdentifier:
method before calling this method. You can also register a set of default supplementary views with the layout object using theregisterClass:forDecorationViewOfKind:
or registerNib:forDecorationViewOfKind:
method.
If you registered a class for the specified identifier and a new cell must be created, this method initializes the cell by calling its initWithFrame:
method. For nib-based cells, this method loads the cell object from the provided nib file. If an existing cell was available for reuse, this method calls the cell’s prepareForReuse
method instead.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
deselectItemAtIndexPath:animated:
Deselects the item at the specified index.
Parameters
- indexPath
-
The index path of the item to select. Specifying
nil
for this parameter removes the current selection. - animated
-
Specify
YES
to animate the change in the selection orNO
to make the change without animating it.
Discussion
If the allowsSelection
property is NO
, calling this method has no effect.
This method does not cause any selection-related delegate methods to be called.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
indexPathForCell:
Returns the index path of the specified cell.
Parameters
- cell
-
The cell object whose index path you want.
Return Value
The index path of the cell or nil
if the specified cell is not in the collection view.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
indexPathForItemAtPoint:
Returns the index path of the item at the specified point in the collection view.
Parameters
- point
-
A point in the collection view’s coordinate system.
Return Value
The index path of the item at the specified point or nil
if no item was found at the specified point.
Discussion
This method relies on the layout information provided by the associated layout object to determine which item contains the point.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
indexPathsForSelectedItems
Returns the index paths for the selected items.
Return Value
An array of NSIndexPath
objects, each of which corresponds to a single selected item. If there are no selected items, this method returns an empty array.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
indexPathsForVisibleItems
Returns an array of the visible items in the collection view.
Return Value
An array of NSIndexPath
objects, each of which corresponds to a visible cell in the collection view. This array does not include any supplementary views that are currently visible. If there are no visible items, this method returns an empty array.
Availability
- Available in iOS 6.0 and later.
See Also
Declared In
UICollectionView.h
initWithFrame:collectionViewLayout:
Initializes and returns a newly allocated collection view object with the specified frame and layout.
Parameters
- frame
-
The frame rectangle for the collection view, measured in points. The origin of the frame is relative to the superview in which you plan to add it. This frame is passed to the superclass during initialization.
- layout
-
The layout object to use for organizing items. The collection view stores a strong reference to the specified object. You may specify
nil
for this parameter.
Return Value
An initialized collection view object or nil
if the object could not be created.
Discussion
Use this method when initializing a collection view object programmatically. If you specify nil
for the layout parameter, you must assign a layout object to the collectionViewLayout
property before displaying the collection view onscreen. If you do not, the collection view will be unable to present any items onscreen.
This method is the designated initializer.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
insertItemsAtIndexPaths:
Inserts new items at the specified index paths.
Parameters
- indexPaths
-
An array of
NSIndexPath
objects, each of which contains a section index and item index at which to insert a new cell. This parameter must not benil
.
Discussion
Call this method to insert one or more new items into the collection view. You might do this when your data source object receives data for new items or in response to user interactions with the collection view. The collection view gets the layout information for the new cells as part of calling this method. And if the layout information indicates that the cells should appear onscreen, the collection view asks your data source to provide the appropriate views, animating them into position as needed.
You can also call this method from a block passed to the performBatchUpdates:completion:
method when you want to animate multiple separate changes into place at the same time. See the description of that method for more information.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
insertSections:
Inserts new sections at the specified indexes.
Parameters
- sections
-
An array of
NSIndexPath
objects, each of which contains the index of a section you want to insert. This parameter must not benil
.
Discussion
Use this method to insert one or more sections into the collection view. This method adds the sections, and it is up to your data source to report the number of items in each section when asked for the information. The collection view then uses that information to get updated layout attributes for the newly inserted sections and items. If the insertions cause a change in the collection view’s visible content, those changes are animated into place.
You can also call this method from a block passed to the performBatchUpdates:completion:
method when you want to animate multiple separate changes into place at the same time. See the description of that method for more information.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
layoutAttributesForItemAtIndexPath:
Returns the layout information for the item at the specified index path.
Parameters
- indexPath
-
The index path of the item.
Return Value
The layout attributes for the item or nil
if no item exists at the specified path.
Discussion
Use this method to retrieve the layout information for a particular item. You should always use this method instead of querying the layout object directly.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
layoutAttributesForSupplementaryElementOfKind:atIndexPath:
Returns the layout information for the specified supplementary view.
Parameters
- kind
-
A string specifying the kind of supplementary view whose layout attributes you want. Layout classes are responsible for defining the kinds of supplementary views they support.
- indexPath
-
The index path of the supplementary view. The interpretation of this value depends on how the layout implements the view. For example, a view associated with a section might contain just a section value.
Return Value
The layout attributes of the supplementary view or nil
if the specified supplementary view does not exist.
Discussion
Use this method to retrieve the layout information for a particular supplementary view. You should always use this method instead of querying the layout object directly.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
moveItemAtIndexPath:toIndexPath:
Moves an item from one location to another in the collection view.
Parameters
- indexPath
-
The index path of the item you want to move. This parameter must not be
nil
. - newIndexPath
-
The index path of the item’s new location. This parameter must not be
nil
.
Discussion
Use this method to reorganize existing data items. You might do this when you rearrange the items within your data source object or in response to user interactions with the collection view. You can move items between sections or within the same section. The collection view updates the layout as needed to account for the move, animating cells into position as needed.
You can also call this method from a block passed to the performBatchUpdates:completion:
method when you want to animate multiple separate changes into place at the same time. See the description of that method for more information.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
moveSection:toSection:
Moves a section from one location to another in the collection view.
Parameters
- section
-
The index path of the section you want to move. This parameter must not be
nil
. - newSection
-
The index path of the section’s new location. This parameter must not be
nil
.
Discussion
Use this method to reorganize existing sections and their contained items. You might do this when you rearrange sections within your data source object or in response to user interactions with the collection view. The collection view updates the layout as needed to account for the move, animating new views into position as needed.
You can also call this method from a block passed to the performBatchUpdates:completion:
method when you want to animate multiple separate changes into place at the same time. See the description of that method for more information.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
numberOfItemsInSection:
Returns the number of items in the specified section.
Parameters
- section
-
The index of the section for which you want a count of the items.
Return Value
The number of items in the specified section.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
numberOfSections
Returns the number of sections displayed by the collection view.
Return Value
The number of sections in the collection view.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
performBatchUpdates:completion:
Animates multiple insert, delete, reload, and move operations as a group.
Parameters
- updates
-
The block that performs the relevant insert, delete, reload, or move operations.
- completion
-
A completion handler block to execute when all of the operations are finished. This block takes a single Boolean parameter that contains the value
YES
if all of the related animations completed successfully orNO
if they were interrupted. This parameter may benil
.
Discussion
You can use this method in cases where you want to insert, delete, reload or move cells around the collection view in one single animated operation, as opposed to in several separate animations. Use the blocked passed in the updatesparameter to specify all of the operations you want to perform.
When you group operations to insert, delete, reload, or move sections inside a single batch job, all operations are performed based on the current indexes of the collection view. This is unlike modifying a mutable array where the insertion or deletion of items affects the indexes of successive operations. Therefore, you do not have to remember which items or sections were inserted, deleted, or moved and adjust the indexes of all other operations accordingly.
Availability
- Available in iOS 6.0 and later.
See Also
Declared In
UICollectionView.h
registerClass:forCellWithReuseIdentifier:
Register a class for use in creating new collection view cells.
Parameters
- cellClass
-
The class of a cell that you want to use in the collection view.
- identifier
-
The reuse identifier to associate with the specified class. This parameter must not be
nil
and must not be an empty string.
Discussion
Prior to calling the dequeueReusableCellWithReuseIdentifier:forIndexPath:
method of the collection view, you must use this method or the registerNib:forCellWithReuseIdentifier:
method to tell the collection view how to create a new cell of the given type. If a cell of the specified type is not currently in a reuse queue, the collection view uses the provided information to create a new cell object automatically.
If you previously registered a class or nib file with the same reuse identifier, the class you specify in the cellClassparameter replaces the old entry. You may specify nil
for cellClass if you want to unregister the class from the specified reuse identifier.
Availability
- Available in iOS 6.0 and later.
See Also
Declared In
UICollectionView.h
registerClass:forSupplementaryViewOfKind:withReuseIdentifier:
Registers a class for use in creating supplementary views for the collection view.
Parameters
- viewClass
-
The class to use for the supplementary view.
- elementKind
-
The kind of supplementary view to create. This value is defined by the layout object. This parameter must not be
nil
. - identifier
-
The reuse identifier to associate with the specified class. This parameter must not be
nil
and must not be an empty string.
Discussion
Prior to calling the dequeueReusableSupplementaryViewOfKind:withReuseIdentifier:forIndexPath:
method of the collection view, you must use this method or theregisterNib:forSupplementaryViewOfKind:withReuseIdentifier:
method to tell the collection view how to create a supplementary view of the given type. If a view of the specified type is not currently in a reuse queue, the collection view uses the provided information to create a view object automatically.
If you previously registered a class or nib file with the same element kind and reuse identifier, the class you specify in the viewClass parameter replaces the old entry. You may specify nil
for viewClass if you want to unregister the class from the specified element kind and reuse identifier.
Availability
- Available in iOS 6.0 and later.
See Also
Declared In
UICollectionView.h
registerNib:forCellWithReuseIdentifier:
Register a nib file for use in creating new collection view cells.
Parameters
- nib
-
The nib object containing the cell object. The nib file must contain only one top-level object and that object must be of the type
UICollectionViewCell
. - identifier
-
The reuse identifier to associate with the specified nib file. This parameter must not be
nil
and must not be an empty string.
Discussion
Prior to calling the dequeueReusableCellWithReuseIdentifier:forIndexPath:
method of the collection view, you must use this method or the registerClass:forCellWithReuseIdentifier:
method to tell the collection view how to create a new cell of the given type. If a cell of the specified type is not currently in a reuse queue, the collection view uses the provided information to create a new cell object automatically.
If you previously registered a class or nib file with the same reuse identifier, the object you specify in the nibparameter replaces the old entry. You may specify nil
for nib if you want to unregister the nib file from the specified reuse identifier.
Availability
- Available in iOS 6.0 and later.
See Also
Declared In
UICollectionView.h
registerNib:forSupplementaryViewOfKind:withReuseIdentifier:
Registers a nib file for use in creating supplementary views for the collection view.
Parameters
- nib
-
The nib object containing the view object. The nib file must contain only one top-level object and that object must be of the type
UICollectionViewCell
. - kind
-
The kind of supplementary view to create. This value is defined by the layout object. This parameter must not be
nil
. - identifier
-
The reuse identifier to associate with the specified nib file. This parameter must not be
nil
and must not be an empty string.
Discussion
Prior to calling the dequeueReusableSupplementaryViewOfKind:withReuseIdentifier:forIndexPath:
method of the collection view, you must use this method or theregisterClass:forSupplementaryViewOfKind:withReuseIdentifier:
method to tell the collection view how to create a supplementary view of the given type. If a view of the specified type is not currently in a reuse queue, the collection view uses the provided information to create a view object automatically.
If you previously registered a class or nib file with the same element kind and reuse identifier, the class you specify in the viewClass parameter replaces the old entry. You may specify nil
for nib if you want to unregister the class from the specified element kind and reuse identifier.
Availability
- Available in iOS 6.0 and later.
See Also
Declared In
UICollectionView.h
reloadData
Reloads all of the data for the collection view.
Discussion
Call this method to reload all of the items in the collection view. This causes the collection view to discard any currently visible items and redisplay them. For efficiency, the collection view only displays those cells and supplementary views that are visible. If the collection data shrinks as a result of the reload, the collection view adjusts its scrolling offsets accordingly.
You should not call this method in the middle of animation blocks where items are being inserted or deleted. Insertions and deletions automatically cause the table’s data to be updated appropriately.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
reloadItemsAtIndexPaths:
Reloads just the items at the specified index paths.
Parameters
- indexPaths
-
An array of
NSIndexPath
objects identifying the items you want to update.
Discussion
Call this method to selectively reload only the specified items. This causes the collection view to discard any cells associated with those items and redisplay them.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
reloadSections:
Reloads the data in the specified sections of the collection view.
Parameters
- sections
-
The indexes of the sections to reload.
Discussion
Call this method to selectively reload only the items in the specified sections. This causes the collection view to discard any cells associated with those items and redisplay them.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
scrollToItemAtIndexPath:atScrollPosition:animated:
Scrolls the collection view contents until the specified item is visible.
Parameters
- indexPath
-
The index path of the item to scroll into view.
- scrollPosition
-
An option that specifies where the item should be positioned when scrolling finishes. For a list of possible values, see
“UICollectionViewScrollPosition”
. - animated
-
Specify
YES
to animate the scrolling behavior orNO
to adjust the scroll view’s visible content immediately.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
selectItemAtIndexPath:animated:scrollPosition:
Selects the item at the specified index path and optionally scrolls it into view.
Parameters
- indexPath
-
The index path of the item to select. Specifying
nil
for this parameter clears the current selection. - animated
-
Specify
YES
to animate the change in the selection orNO
to make the change without animating it. - scrollPosition
-
An option that specifies where the item should be positioned when scrolling finishes. For a list of possible values, see
“UICollectionViewScrollPosition”
.
Discussion
If the allowsSelection
property is NO
, calling this method has no effect. If there is an existing selection with a different index path and the allowsMultipleSelection
property is NO
, calling this method replaces the previous selection.
This method does not cause any selection-related delegate methods to be called.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
setCollectionViewLayout:animated:
Assigns a new layout object to the collection view and optionally animates the change.
Parameters
- layout
-
The new layout object to use to organize the collected views.
- animated
-
Specify
YES
if you want to animate changes from the current layout to the new layout specified by the layoutparameter. SpecifyNO
to make the change without animations.
Discussion
When animating layout changes, the animation timing and parameters are controlled by the collection view.
Availability
- Available in iOS 6.0 and later.
Declared In
UICollectionView.h
visibleCells
Returns an array of visible cells currently displayed by the collection view.
Return Value
An array of UICollectionViewCell
objects. If no cells are visible, this method returns an empty array.
Discussion
This method returns the complete list of visible cells displayed by the collection view.
Availability
- Available in iOS 6.0 and later.
See Also
Declared In
UICollectionView.h
Constants
UICollectionViewScrollPosition
Constants that indicate how to scroll an item into the visible portion of the collection view.
enum {
UICollectionViewScrollPositionNone = 0,
UICollectionViewScrollPositionTop = 1 << 0,
UICollectionViewScrollPositionCenteredVertically = 1 << 1,
UICollectionViewScrollPositionBottom = 1 << 2, UICollectionViewScrollPositionLeft = 1 << 3,
UICollectionViewScrollPositionCenteredHorizontally = 1 << 4,
UICollectionViewScrollPositionRight = 1 << 5
};
typedef NSUInteger UICollectionViewScrollPosition;
Constants
UICollectionViewScrollPositionNone
-
Do not scroll the item into view.
Available in iOS 6.0 and later.
Declared in
UICollectionView.h
.
UICollectionViewScrollPositionTop
-
Scroll so that the item is positioned at the top of the collection view’s bounds. This option is mutually exclusive with the
UICollectionViewScrollPositionCenteredVertically
andUICollectionViewScrollPositionBottom
options.Available in iOS 6.0 and later.
Declared in
UICollectionView.h
.
UICollectionViewScrollPositionCenteredVertically
-
Scroll so that the item is centered vertically in the collection view. This option is mutually exclusive with the
UICollectionViewScrollPositionTop
andUICollectionViewScrollPositionBottom
options.Available in iOS 6.0 and later.
Declared in
UICollectionView.h
.
UICollectionViewScrollPositionBottom
-
Scroll so that the item is positioned at the bottom of the collection view’s bounds. This option is mutually exclusive with the
UICollectionViewScrollPositionTop
andUICollectionViewScrollPositionCenteredVertically
options.Available in iOS 6.0 and later.
Declared in
UICollectionView.h
.
UICollectionViewScrollPositionLeft
-
Scroll so that the item is positioned at the left edge of the collection view’s bounds. This option is mutually exclusive with the
UICollectionViewScrollPositionCenteredHorizontally
andUICollectionViewScrollPositionRight
options.Available in iOS 6.0 and later.
Declared in
UICollectionView.h
.
UICollectionViewScrollPositionCenteredHorizontally
-
Scroll so that the item is centered horizontally in the collection view. This option is mutually exclusive with the
UICollectionViewScrollPositionLeft
andUICollectionViewScrollPositionRight
options.Available in iOS 6.0 and later.
Declared in
UICollectionView.h
.
UICollectionViewScrollPositionRight
-
Scroll so that the item is positioned at the right edge of the collection view’s bounds. This option is mutually exclusive with the
UICollectionViewScrollPositionLeft
andUICollectionViewScrollPositionCenteredHorizontally
options.Available in iOS 6.0 and later.
Declared in
UICollectionView.h
.
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