带有空默认选项的微调控制项

I have a Spinner which gets populate using a SimpleCursorAdapter. My cursor has some values, but i need the Spinner to show an empty option by default.

我有一个Spinner，它使用SimpleCursorAdapter填充。我的光标有一些值，但是我需要微调器在默认情况下显示一个空选项。

I don't want to use ArrayAdapter<String>, or CursorWrapper in this app, for some reason.

由于某些原因，我不想在这个应用程序中使用ArrayAdapter 或CursorWrapper。

There should be a simpler way to show an empty option in the Spinner by default.

在默认情况下，应该有一种更简单的方法在微调器中显示空选项。

4 个解决方案

#1

You can simply hide the unwanted view in the spinner adapter (getDropDownView ) :

您可以简单地将不想要的视图隐藏在spinner适配器(getDropDownView)中:

In my sample code, defaultposition is the position to hide (like a "Select value" position)

在我的示例代码中，defaultposition是隐藏的位置(比如“选择值”位置)

public class SpinnerOptionAdapter extends ArrayAdapter<optionsInfos> {

 ...

   @Override

  public View getDropDownView(int position, View convertView, ViewGroup parent)
  {   // This view starts when we click the spinner.
    View row = convertView;
    if(row == null)
    {
        LayoutInflater inflater = context.getLayoutInflater();
        row = inflater.inflate(R.layout.product_tab_produit_spinner_layout, parent, false);
    }

    ...

    optionsInfos item = data.get(position);


    if( (item != null) && ( position == defaultposition)) {
        row.setVisibility(View.GONE);
    } else {
        row.setVisibility(View.VISIBLE);
    }

   ....

    return row;
}


 ...
}

#2

Spinner's OnItemSelectedListener runs on the compile time as well that fetches the first item to view on the Spinner selected item.

Spinner的OnItemSelectedListener也在编译时运行，它获取第一个要在Spinner选中的项上查看的项。

Add a dummy item (String - null " ") on your SimpleCursorAdapter and use spinner.setSelected(int thatSpecificPostionYouJustAdded).

在SimpleCursorAdapter上添加一个虚拟项(String - null ")并使用微调器。setSelected(int thatSpecificPostionYouJustAdded)。

#3

A method I sometimes use to add an extra record such as an "empty" option with a SimpleCursorAdapter destined for a Spinner is by using a UNION clause in my cursor query. EMPTY_SPINNER_STRING could be something like: "-- none specified --" or similar. Use an "order by" clause to get your empty record first and therefore the default value in the Spinner. A crude but effective way of getting the required result without changing the underlying table data. In my example I only want certain spinners to have a default empty value (those with a modifier type of "intensity".

我有时用来添加额外记录的方法是，在我的游标查询中使用UNION子句，例如“empty”选项，带有一个为微调器指定的SimpleCursorAdapter。EMPTY_SPINNER_STRING可以是:“——没有指定——”或类似的。使用“order by”子句首先获取空记录，因此是微调器中的默认值。一种简单但有效的方法，可以在不更改底层表数据的情况下获得所需的结果。在我的示例中，我只希望某些spinners具有默认的空值(具有修饰符类型的“强度”)。

public Cursor getLOV(String modifier_type)
//get the list of values (LOVS) for a given modifier
{
    if (mDb == null)
    {
        this.open();
    }
    try {
        MYSQL = "SELECT _ID AS '_id', code, name, type as 'DESC', ordering FROM "+codeTab+" WHERE type = '"+modifier_type+"'" +
                " ORDER BY ordering, LOWER(name)";
        if (modifier_type.equals("intensity")) { //then include a default empty record
            MYSQL = "SELECT _ID AS '_id', code, name as 'NAME', type as 'DESC', ordering FROM "+codeTab+" WHERE type = '"+modifier_type+"'" +
                    " UNION SELECT 9999 AS '_id', '' AS 'code', '"+EMPTY_SPINNER_STRING+"' AS 'NAME', 'intensity' AS 'DESC', 1 AS ordering ORDER BY ordering, name";
        }
        Log.d(TAG, "MYSQL = "+MYSQL);
        return mDb.rawQuery(MYSQL, null);
    }
    catch (SQLiteException exception) {
        Log.e("Database LOV query", exception.getLocalizedMessage());
        return null;
    }
}

#4

After setting the adapter. call setSelection (i used with 0) and right after that set the text color to transparent.

后设置适配器。调用setSelection(我使用了0)，然后将文本颜色设置为透明。

    // Preselect the first to make the spinner text transparent
    spinner.setSelection(0, false);
    TextView selectedView = (TextView) spinner.getSelectedView();
    if (selectedView != null) {
        selectedView.setTextColor(getResources().getColor(R.color.transparent));
    }

Then, set your OnItemSelectedListener (if needed).

然后，设置OnItemSelectedListener(如果需要)。

    spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {

        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
        }

        @Override
        public void onNothingSelected(AdapterView<?> parent) {
        }
    });

This will make the spinner empty at first time seen. But, if the user will select the first item it will do nothing because 0 is pre selected. For fixing this i used this subclass of spinner. taken from @melquiades's answer:

这将使转轮第一次看到空。但是，如果用户将选择第一个项目，它将不做任何事情，因为0是预先选择的。为了解决这个问题，我使用了spinner的子类。取自@melquiades的回答是:

/** 
  * Spinner extension that calls onItemSelected even when the selection is the same as its previous value
  */
public class FVRSpinner extends Spinner {

    public FVRSpinner(Context context) {
        super(context);
    }

    public FVRSpinner(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public FVRSpinner(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    public void setSelection(int position, boolean animate) {
        boolean sameSelected = position == getSelectedItemPosition();
        super.setSelection(position, animate);
        if (sameSelected) {
            // Spinner does not call the OnItemSelectedListener if the same item is selected, so do it manually now
            if (getOnItemSelectedListener() != null) {
                getOnItemSelectedListener().onItemSelected(this, getSelectedView(), position, getSelectedItemId());
            }
        }
    }

    @Override
    public void setSelection(int position) {
        boolean sameSelected = position == getSelectedItemPosition();
        super.setSelection(position);
        if (sameSelected) {
            // Spinner does not call the OnItemSelectedListener if the same item is selected, so do it manually now
            if (getOnItemSelectedListener() != null) {
                getOnItemSelectedListener().onItemSelected(this, getSelectedView(), position, getSelectedItemId());
            }
        }
    }
}