Android流式布局FlowLayout

背景介绍：

最近需要做一个类似于Java awt包里的FlowLayout的流式布局，比如下图

Android原生控件中没有找到现成的，习惯先Google之，找到鸿洋_ 大神的： Android 自定义ViewGroup 实战篇 -> 实现FlowLayout。

写的太好了，基本实现了流式布局的功能，不过还有些功能没有实现：

• flowLayout自身的padding

• 子view的visibility为gone时隐藏

• 兼容子view的居中显示

在大神的基础上进行继续开发，实现以上功能，并优化减少在onLayout方法中的一次遍历getChildAt。
FlowLayout的使用方式与系统的LinearLayout、RelativeLayout等基本一样（xml方式和java代码方式创建使用、动态修改、设置事件等）

上代码：

public class FlowLayout extends ViewGroup {

private boolean centerHorizontal;//是否水平居中显示

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

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

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

private void initFromAttributes(Context context, AttributeSet attrs) {
/**
 //res/values/attr.xml
 //<declare-styleable name="FlowLayout">
 // <!-- 是否横向居中 -->
 // <attr name="centerHorizontal" format="boolean" /> 
 //</declare-styleable>
 //下面的代码配合res/values/attr.xml可以支持通过在xml中FlowLayout节点
 //添加app:centerHorizontal="true"的方式设置水平居中属性
 final TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.FlowLayout);
 centerHorizontal = a.getBoolean(R.styleable.FlowLayout_centerHorizontal, centerHorizontal);
 a.recycle();
 */
    }

@Override
protected LayoutParams generateDefaultLayoutParams() {
return new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
    }
@Override
public LayoutParams generateLayoutParams(AttributeSet attrs) {
return new LayoutParams(getContext(), attrs);
    }

@Override
protected LayoutParams generateLayoutParams(ViewGroup.LayoutParams p) {
return new LayoutParams(p.width, p.height);
    }

public boolean isCenterHorizontal() {
return centerHorizontal;
    }

// 动态设置子view的居中状态
public void setCenterHorizontal(boolean centerHorizontal) {
if (this.centerHorizontal ^ centerHorizontal) {
this.centerHorizontal = centerHorizontal;
            requestLayout();
        }
    }

/**
 * 负责设置子控件的测量模式和大小 根据所有子控件设置自己的宽和高
 */
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
// 获得它的父容器为它设置的测量模式和大小
int sizeWidth = MeasureSpec.getSize(widthMeasureSpec);
int sizeHeight = MeasureSpec.getSize(heightMeasureSpec);
int modeWidth = MeasureSpec.getMode(widthMeasureSpec);
int modeHeight = MeasureSpec.getMode(heightMeasureSpec);

// 如果是warp_content情况下，记录宽和高
final int paddingWidth = getPaddingLeft() + getPaddingRight();
final int paddingHeight = getPaddingTop() + getPaddingBottom();
int width = paddingWidth;
int height = paddingHeight;
// 记录每一行的宽度，width不断取最大宽度
int lineWidth = paddingWidth;
// 每一行的高度，累加至height
int lineHeight = 0;
        mAllViews.clear();
        mLineHeight.clear();
        mLineWidth.clear();
// 存储每一行所有的childView
        List<View> lineViews = new ArrayList<>();

int cCount = getChildCount();

// 遍历每个子元素
for (int i = 0; i < cCount; i++) {
            View child = getChildAt(i);
if (child.getVisibility() == GONE) {
continue;
            }
// 得到child的lp
            LayoutParams lp = (LayoutParams) child.getLayoutParams();
// 测量每一个child的宽和高
final int marginWidth = lp.rightMargin + lp.leftMargin;
final int marginHeight = lp.topMargin + lp.bottomMargin;
// 子控件测量的时候需要将父控件的padding和当前子控件的margin算进去
            child.measure(
                getChildMeasureSpec(widthMeasureSpec, paddingWidth + marginWidth, lp.width),
                getChildMeasureSpec(heightMeasureSpec, paddingHeight + marginHeight, lp.height)
            );
// 当前子控件实际占据的宽度
int childWidth = child.getMeasuredWidth() + marginWidth;
// 当前子控件实际占据的高度
int childHeight = child.getMeasuredHeight() + marginHeight;
//如果加入当前child，则超出最大宽度，则得到目前最大宽度给width，累加height 然后开启新行
if (lineWidth + childWidth > sizeWidth) {
                width = Math.max(width, lineWidth);// 取最大的
                height += lineHeight;// 叠加当前高度
// 记录这一行所有的View、总的宽度以及最大高度
                mLineHeight.add(lineHeight);
                mLineWidth.add(lineWidth);
// 将当前行的childView保存，然后开启新的ArrayList保存下一行的childView
                mAllViews.add(lineViews);
                lineViews = new ArrayList<>();
// 重新开启新行，开始记录
                lineWidth = paddingWidth;
                lineHeight = 0;
            }
// 否则累加值lineWidth,lineHeight取最大高度
            lineWidth += childWidth;
            lineHeight = Math.max(lineHeight, childHeight);
// 如果是最后一个，则将当前记录的最大宽度和当前lineWidth做比较
if (i == cCount - 1) {
                width = Math.max(width, lineWidth);
                height += lineHeight;
            }
            lineViews.add(child);
        }
// 记录最后一行
        mLineHeight.add(lineHeight);
        mLineWidth.add(lineWidth);
        mAllViews.add(lineViews);
        setMeasuredDimension((modeWidth == MeasureSpec.EXACTLY) ? sizeWidth
                : width, (modeHeight == MeasureSpec.EXACTLY) ? sizeHeight
                : height);
    }

/**
 * 存储所有的View，按行记录
 */
private List<List<View>> mAllViews = new ArrayList<>();
/**
 * 记录每一行的最大高度
 */
private List<Integer> mLineHeight = new ArrayList<>();
private List<Integer> mLineWidth = new ArrayList<>();

@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
final int paddingLeft = getPaddingLeft();
final int paddingRight = getPaddingRight();
final int paddingTop = getPaddingTop();
final int paddingBottom = getPaddingBottom();
int width = getWidth() - paddingLeft - paddingRight;
int lineHeight;
        List<View> lineViews;
int left = paddingLeft;
int top = paddingTop;
// 得到总行数
int lineNums = mAllViews.size();
for (int i = 0; i < lineNums; i++) {
// 每一行的所有的views
            lineViews = mAllViews.get(i);
// 当前行的最大高度
            lineHeight = mLineHeight.get(i);
if (centerHorizontal) {
int leftRightSpace = width - (mLineWidth.get(i) - paddingLeft - paddingRight);//左右两端空白空间
                left += leftRightSpace / 2;
            }
// 遍历当前行所有的View
for (int j = 0; j < lineViews.size(); j++) {
                View child = lineViews.get(j);
if (child.getVisibility() == View.GONE) {
continue;
                }
                LayoutParams lp = (LayoutParams) child.getLayoutParams();
//计算childView的left,top,right,bottom
int lc = left + lp.leftMargin;
int tc = top + lp.topMargin;
int rc = lc + child.getMeasuredWidth();
int bc = tc + child.getMeasuredHeight();
                rc = Math.min(rc, getWidth() - paddingRight - lp.rightMargin);
                bc = Math.min(bc, getHeight() - paddingBottom - lp.bottomMargin);
                child.layout(lc, tc, rc, bc);//布局子控件
                left += child.getMeasuredWidth() + lp.rightMargin + lp.leftMargin;
            }
            left = paddingLeft;
            top += lineHeight;
        }

    }


public static class LayoutParams extends MarginLayoutParams {

public LayoutParams(Context c, AttributeSet attrs) {
super(c, attrs);
        }

public LayoutParams(ViewGroup.LayoutParams source) {
super(source);
        }

public LayoutParams(MarginLayoutParams source) {
super(source);
        }

public LayoutParams(int width, int height) {
super(width, height);
        }
    }
}