Android自定义ViewGroup，onMeasure、onLayout，实现流式布局

Android自定义ViewGroup，onMeasure、onLayout，实现流式布局

其实自定义ViewGroup与自定义View很像。它们本质都是View，区别在于ViewGroup是用来组织显示View的。自定义ViewGroup也有几个关键的方法需要实现，而且onLayout方法是必须实现的。在自定义ViewGroup中我们常常需要重写onMeasure、onLayout，而onDraw一般不需要重写。

onMeasure(int widthMeasureSpec, int heightMeasureSpec)

这个方法是用来测试量尺寸的，这两个参数是父布局传递过来的。如果你自定义的ViewGroup已经是根布局，但是它一样有父布局，因为android系统最后都会将其被添加到一个FrameLayout布局里。这个方法不仅要测量ViewGroup的尺寸，那还必须测量ViewGroup内每个视图。测试子视图把这两个参数传递过去，剩下的就是子视图自己的onMeasure方法来测量出它自己的尺寸。这方法的参数各自都包含了测量模式和具体尺寸大小。我们根据不同的测量模式来决定其具体的尺寸。具体的测量模式两三种：

UNSPECIFIED：父布局没有任何限制（在自定义View或ViewGroup中都不常用这个）EXACTLY：父布局已经确定了确切的尺寸AT_MOST：可以任意大小，直到指定确切的尺寸

我们只关注后面两种。这个模式的选定是根据xml布局文件中android:layout_width和android:layout_height的取值情况来决定的：

EXACTLY模式：(1)match_parent：占满整个父布局的宽或高(2)具体的数值：如300dpAT_MOST模式：(1)wrap_content：期望内容多大，宽和高相应多大，反正是能够包裹住内容。这个模式给过来时，大小是不会像如期望一样大小，它就是整个父布局的大小，因为父布局没有办法知道你的内容有多大，你必须在onMeasure方法亲自确定其大小。

从两个参数取出各自的测量模式与尺寸：

int measuredWidthMode = MeasureSpec.getMode(widthMeasureSpec);int measuredWidthSize = MeasureSpec.getSize(widthMeasureSpec);int measuredHeightMode = MeasureSpec.getMode(heightMeasureSpec);int measuredHeightSize = MeasureSpec.getSize(heightMeasureSpec);

对于EXACTLY模式，ViewGroup的尺寸直接用分离出来的尺寸。而对于AT_MOST模式的，分离出来的尺寸不能直接使用，因为它是传过来的尺寸是父布局的尺寸，明显不符合我们的要求。我们要根据需要，计算出ViewGroup中的子视图尺寸并累加起来作为最终的尺寸，在这种模式下，还要考虑各个视图之间的外边距margin（在自定义View，则只需要考虑内边距padding）。

@Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); int measuredWidthMode = MeasureSpec.getMode(widthMeasureSpec); int measuredWidthSize = MeasureSpec.getSize(widthMeasureSpec); int measuredHeightMode = MeasureSpec.getMode(heightMeasureSpec); int measuredHeightSize = MeasureSpec.getSize(heightMeasureSpec); int rowWidth = 0;// 临时记录行宽 int rowHeight = 0;// 临时记录行高 int maxWith = 0; int maxHeight = 0; measureChildren(widthMeasureSpec, heightMeasureSpec);// 测量children的大小 int count = getChildCount(); if (count != 0) { for (int i = 0; i < count; i++) { View child = getChildAt(i); measureChild(child, widthMeasureSpec, heightMeasureSpec); MarginLayoutParams mlp = (MarginLayoutParams) child.getLayoutParams(); int childWidth = child.getMeasuredWidth() + mlp.rightMargin + mlp.rightMargin; int childHeight = child.getMeasuredHeight() + mlp-Margin + mlp.bottomMargin; if (childWidth + rowWidth > measuredWidthSize - getPaddingLeft() - getPaddingRight()) { // 换行 maxWith = Math.max(maxWith, rowWidth); rowWidth = childWidth; maxHeight += rowHeight; rowHeight = childHeight; } else { // 不换行 rowWidth += childWidth; rowHeight = Math.max(childHeight, rowHeight); } //最后一个控件 if (i == count - 1) { maxWith = Math.max(maxWith, rowWidth); maxHeight += rowHeight; } } } String widthModeStr = null; switch (measuredWidthMode) { case MeasureSpec.AT_MOST: widthModeStr = "AT_MOST"; if (count == 0) { mWidth = 0; } else { mWidth = maxWith + getPaddingLeft() + getPaddingRight(); } break; case MeasureSpec.EXACTLY: widthModeStr = "EXACTLY"; mWidth = getPaddingLeft() + getPaddingRight() + measuredWidthSize; break; default: throw new IllegalStateException("Unexpected value: " + measuredWidthMode); case MeasureSpec.UNSPECIFIED: break; } String heightModeStr = null; switch (measuredHeightMode) { case MeasureSpec.AT_MOST: heightModeStr = "AT_MOST"; if (count == 0) { mHeight = 0; } else { mHeight = maxHeight + getPaddingTop() + getPaddingBottom(); } break; case MeasureSpec.EXACTLY: heightModeStr = "EXACTLY"; mHeight = getPaddingTop() + getPaddingBottom() + measuredHeightSize; break; default: throw new IllegalStateException("Unexpected value: " + measuredHeightMode); case MeasureSpec.UNSPECIFIED: break; } setMeasuredDimension(mWidth, mHeight); String str = "@widthMode#" + widthModeStr + ":" + measuredWidthSize + "@heightMode#" + heightModeStr + ":" + measuredHeightSize; Log.d("Layout尺寸", str); }

因为我们在处理AT_MOST模式时，必须获得每个子视图的外边距信息：

MarginLayoutParams mlp = (MarginLayoutParams) child.getLayoutParams();

所以必须加入以下代码，否则会报错：

// 自定义ViewGroup必须要有以下这个方法，否则拿不到child的margin的信息 @Override public ViewGroup.LayoutParams generateLayoutParams(AttributeSet attrs) { return new MarginLayoutParams(getContext(), attrs); }

onLayout(boolean changed, int l, int t, int r, int b)

在自定义View中一般不需要重写这个方法，但是在自定义ViewGroup中必须重写这个方法，因为ViewGroup是View的集合，必须处理它们的位置关系。

@Override protected void onLayout(boolean changed, int l, int t, int r, int b) { if (changed) { int count = getChildCount(); for (int i = 0; i < count; i++) { View child = getChildAt(i); Log.i("Child大小W", child.getMeasuredWidth() + "#H:" + child.getMeasuredHeight()); ChildPosition pos = mChildPos.get(i); //设置View的左边、上边、右边底边位置 child.layout(pos.left, pos-, pos.right, pos.bottom); } } }

小结

所以自定义ViewGroup还是相当简单的。因为我们只需要量好ViewGroup的视图，在测量过程中，比较值得注意的就是当模式是AT_MOST时，需要计算各个子View的尺寸再累加起来，得到就是ViewGroup的尺寸。onMeasure的参数都是父布局传给子控件的，这就是为什么在自定义ViewGroup中，测量子View时的这两个参数是来自定义的ViewGroup。最后就是就是在onLayout中布局子View的位置。

流式布局

我们继承ViewGroup定义一个流式布局CustomFlowLayout。在流式布局中，我额外增加了滚动的功能，因为当我们的内容超过我们自定义ViewGroup的可视范围后，就需要用到滚动功能。滚动功能的实现思路：

首先重写onTouchEvent方法，消费滑动事件，根据我们的手指滑动的方向，来移动我们的视图。添加上边界的检查，一旦到达上边界就不允许再滚动添加下边界的检查，一旦到达下边界就不允许再滚动

那么在处理边界问题时，需要我们有一定的知识储备，就是以下这个方面的知识：

android的事件传递方面，Activity->View group ->View，这可以了事件传递的顺序。android的事件传递机制，要了解好dispatchTouchEvent、onInterceptTouchEvent、onTouchEvent这个方法的工作过程，明白谁消费了事件，谁传递了事件。理解好scrollTo与scrollBy的区别，前者是绝对位置移动，后者是相对位置移动。要理解getY与getRawY与getScrollY它们的坐标系的特点。最后一点，要知道android屏幕的坐标系是无限大，布局视图并没有边界，我们的屏幕只是这个坐标系的一部分，显示出来的视图只是刚好在这一部分而已。、我们滚动视图，实质是改变了视图整体的位置而已。

下面是一个完全的流式布局CustomFlowLayout:

package com.wong.customtextview;import android.content.Context;import android.util.AttributeSet;import android.util.Log;import android.view.MotionEvent;import android.view.View;import android.view.ViewConfiguration;import android.view.ViewGroup;import android.widget.Scroller;import java.util.ArrayList;import java.util.List;public class CustomFlowLayout extends ViewGroup { private int mWidth = 0; private int mHeight = 0; private int realHeight; private boolean scrollable = false; private boolean isInterceptedTouch; /** * 判定为拖动的最小移动像素数 */ private int mTouchSlop; private int topBorder; // 上边界 private int bottomBorder;// 下边界 //记录每个View的位置 private List mChildPos = new ArrayList(); private static class ChildPosition { int left, top, right, bottom; public ChildPosition(int left, int top, int right, int bottom) { this.left = left; this- = top; this.right = right; this.bottom = bottom; } } public CustomFlowLayout(Context context) { this(context, null); } public CustomFlowLayout(Context context, AttributeSet attrs) { this(context, attrs, 0); } public CustomFlowLayout(Context context, AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); ViewConfiguration configuration = ViewConfiguration.get(context); // 获取TouchSlop值,用于判断当前用户的操作是否是拖动 mTouchSlop = configuration.getScaledPagingTouchSlop(); } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); int measuredWidthMode = MeasureSpec.getMode(widthMeasureSpec); int measuredWidthSize = MeasureSpec.getSize(widthMeasureSpec); int measuredHeightMode = MeasureSpec.getMode(heightMeasureSpec); int measuredHeightSize = MeasureSpec.getSize(heightMeasureSpec); int rowWidth = 0;// 临时记录行宽 int rowHeight = 0;// 临时记录行高 int maxWith = 0; int maxHeight = 0; measureChildren(widthMeasureSpec, heightMeasureSpec);// 测量children的大小 int count = getChildCount(); if (count != 0) { for (int i = 0; i < count; i++) { View child = getChildAt(i); MarginLayoutParams mlp = (MarginLayoutParams) child.getLayoutParams(); int childWidth = child.getMeasuredWidth() + mlp.rightMargin + mlp.rightMargin; int childHeight = child.getMeasuredHeight() + mlp-Margin + mlp.bottomMargin; if (childWidth + rowWidth > measuredWidthSize - getPaddingLeft() - getPaddingRight()) { // 换行 maxWith = Math.max(maxWith, rowWidth); rowWidth = childWidth; maxHeight += rowHeight; rowHeight = childHeight; } else { rowWidth += childWidth; rowHeight = Math.max(childHeight, rowHeight); } //最后一个控件 if (i == count - 1) { maxWith = Math.max(maxWith, rowWidth); maxHeight += rowHeight; } } } String widthModeStr = null; switch (measuredWidthMode) { case MeasureSpec.AT_MOST: widthModeStr = "AT_MOST"; if (count == 0) { mWidth = 0; } else { mWidth = maxWith + getPaddingLeft() + getPaddingRight(); } break; case MeasureSpec.EXACTLY: widthModeStr = "EXACTLY"; mWidth = getPaddingLeft() + getPaddingRight() + measuredWidthSize; break; default: throw new IllegalStateException("Unexpected value: " + measuredWidthMode); case MeasureSpec.UNSPECIFIED: break; } String heightModeStr = null; switch (measuredHeightMode) { case MeasureSpec.AT_MOST: heightModeStr = "AT_MOST"; if (count == 0) { mHeight = 0; } else { mHeight = maxHeight + getPaddingTop() + getPaddingBottom(); } break; case MeasureSpec.EXACTLY: heightModeStr = "EXACTLY"; mHeight = getPaddingTop() + getPaddingBottom() + measuredHeightSize; break; default: throw new IllegalStateException("Unexpected value: " + measuredHeightMode); case MeasureSpec.UNSPECIFIED: break; } //真实高度 realHeight = maxHeight + getPaddingTop() + getPaddingBottom(); //测量高度 if (measuredHeightMode == MeasureSpec.EXACTLY) { scrollable = realHeight > mHeight; } else { scrollable = realHeight > measuredHeightSize; } if (scrollable) { // 初始化上下边界值 MarginLayoutParams lp1 = (MarginLayoutParams) getChildAt(0).getLayoutParams(); topBorder = getChildAt(0).getTop() - lp1-Margin; if (measuredHeightMode == MeasureSpec.EXACTLY) { bottomBorder = realHeight - mHeight + getPaddingBottom(); } else { bottomBorder = realHeight - measuredHeightSize + getPaddingBottom(); } } setMeasuredDimension(mWidth, mHeight); String str = "@widthMode#" + widthModeStr + ":" + measuredWidthSize + "@heightMode#" + heightModeStr + ":" + measuredHeightSize; Log.d("Layout尺寸", str); } @Override protected void onLayout(boolean changed, int l, int t, int r, int b) { mChildPos.clear(); int rowWidth = 0;// 临时记录行宽 int rowHeight = 0;// 临时记录行高 int maxWith = 0; int maxHeight = 0; int count = getChildCount(); for (int i = 0; i < count; i++) { View child = getChildAt(i); MarginLayoutParams mlp = (MarginLayoutParams) child.getLayoutParams(); int childWidth = child.getMeasuredWidth() + mlp.rightMargin + mlp.rightMargin; int childHeight = child.getMeasuredHeight() + mlp-Margin + mlp.bottomMargin; if (childWidth + rowWidth > getMeasuredWidth() - getPaddingLeft() - getPaddingRight()) { // 换行 maxWith = Math.max(maxWith, rowWidth); rowWidth = childWidth; maxHeight += rowHeight; rowHeight = childHeight; mChildPos.add(new ChildPosition( getPaddingLeft() + mlp.leftMargin, getPaddingTop() + maxHeight + mlp-Margin, getPaddingLeft() + childWidth - mlp.rightMargin, getPaddingTop() + maxHeight + childHeight - mlp.bottomMargin )); } else { // 不换行 mChildPos.add(new ChildPosition( getPaddingLeft() + rowWidth + mlp.leftMargin, getPaddingTop() + maxHeight + mlp-Margin, getPaddingLeft() + rowWidth + childWidth - mlp.rightMargin, getPaddingTop() + maxHeight + childHeight - mlp.bottomMargin )); rowWidth += childWidth; rowHeight = Math.max(childHeight, rowHeight); } } // 布局每一个child for (int i = 0; i < count; i++) { View child = getChildAt(i); Log.i("Child大小W", child.getMeasuredWidth() + "#H:" + child.getMeasuredHeight()); ChildPosition pos = mChildPos.get(i); //设置View的左边、上边、右边底边位置 child.layout(pos.left, pos-, pos.right, pos.bottom); } } // 自定义ViewGroup必须要有以下这个方法，否则拿不到child的margin的信息 @Override public ViewGroup.LayoutParams generateLayoutParams(AttributeSet attrs) { return new MarginLayoutParams(getContext(), attrs); } private float mLastYMove; private float currentY; @Override public boolean onTouchEvent(MotionEvent event) { if (scrollable) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: this.mLastYMove = event.getRawY(); break; case MotionEvent.ACTION_MOVE: this.currentY = event.getRawY(); int scrolledY = getScrollY(); float diff = Math.abs(this.mLastYMove - this.currentY); // 当手指拖动值大于TouchSlop值时，认为应该进行滚动，拦截子控件的事件 if (diff > mTouchSlop) { int dy = (int) (this.mLastYMove - this.currentY); if (scrolledY + dy < topBorder) { dy = 0; scrollTo(0, topBorder); return true; //最顶端，超过0时，不再下拉，要是不设置这个，getScrollY一直是负数 } else if (scrolledY + dy > bottomBorder) { dy = 0; scrollTo(0, bottomBorder); return true; } scrollBy(0, dy); this.mLastYMove = event.getRawY(); } break; } } return true; }}

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