Android自定义ViewGroup，onMeasureonLayout，实现流式布局
Posted SamDlex
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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300dp - AT_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.topMargin + 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.top, 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<ChildPosition> mChildPos = new ArrayList<ChildPosition>();
private static class ChildPosition
int left, top, right, bottom;
public ChildPosition(int left, int top, int right, int bottom)
this.left = left;
this.top = 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.topMargin + 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.topMargin;
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.topMargin + 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.topMargin,
getPaddingLeft() + childWidth - mlp.rightMargin,
getPaddingTop() + maxHeight + childHeight - mlp.bottomMargin
));
else
// 不换行
mChildPos.add(new ChildPosition(
getPaddingLeft() + rowWidth + mlp.leftMargin,
getPaddingTop() + maxHeight + mlp.topMargin,
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.top, 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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