android之自定义ViewGroup和自动换行的布局的实现

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viewgroup简单说就是可以装view的view.今天遇到一个问题，就是需要一个可以自动根据一行中view的宽度自动换行的布局，网上

找了下，没有相关的例子，但是找到了思路：自定义一个viewgroup,然后在onlayout文件里面自动检测view的右边缘的横坐标值，

和你的view的parent view的况度判断是否换行显示view就可以了。因为代码比较简单，就不多说了：

package com.mayi.meal.view;import android.content.Context;import android.graphics.Canvas;import android.util.AttributeSet;import android.util.Log;import android.view.View;import android.view.ViewGroup;public class MyViewGroup extends ViewGroup {private final static String TAG = "MyViewGroup";private final static int VIEW_MARGIN = 2;// Simple constructor to use when creating a view from code.public MyViewGroup(Context context, AttributeSet attrs, int defStyle) {super(context, attrs, defStyle);// TODO Auto-generated constructor stub}// Constructor that is called when inflating a view from XML.public MyViewGroup(Context context, AttributeSet attrs) {super(context, attrs);}// Simple constructor to use when creating a view from code.public MyViewGroup(Context context) {super(context);}@Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {Log.i(TAG, "onMeasure.....");Log.d(TAG, "widthMeasureSpec = " + widthMeasureSpec+ " heightMeasureSpec" + heightMeasureSpec);for (int index = 0; index < getChildCount(); index++) {final View child = getChildAt(index);// measurechild.measure(MeasureSpec.UNSPECIFIED, MeasureSpec.UNSPECIFIED);}//this.setMeasuredDimension(widthMeasureSpec, heightMeasureSpec);super.onMeasure(widthMeasureSpec, heightMeasureSpec);}@Overrideprotected void onLayout(boolean arg0, int arg1, int arg2, int arg3, int arg4) {Log.i(TAG, "onLayout.....");Log.d(TAG, "changed = " + arg0 + " left = " + arg1 + " top = " + arg2+ " right = " + arg3 + " botom = " + arg4);final int count = getChildCount();int row = 0; // which row lay you view relative to parentint lengthX = arg1; // right position of child relative to parentint lengthY = arg2; // bottom position of child relative to parentfor (int i = 0; i < count; i++) {final View child = this.getChildAt(i);int width = child.getMeasuredWidth();int height = child.getMeasuredHeight();lengthX += width + VIEW_MARGIN;lengthY = row * (height + VIEW_MARGIN) + VIEW_MARGIN + height+ arg2;// if it can't drawing on a same line , skip to next lineif (lengthX > arg3) {lengthX = width + VIEW_MARGIN + arg1;row++;lengthY = row * (height + VIEW_MARGIN) + VIEW_MARGIN + height+ arg2;}child.layout(lengthX - width, lengthY - height, lengthX, lengthY);}}}

这里有个地方要注意，那就要明白ViewGroup的绘图流程：ViewGroup绘制包括两个步骤：1.measure 2.layout

　　在两个步骤中分别调用回调函数：1.onMeasure() 2.onLayout()

　　1.onMeasure() 在这个函数中，ViewGroup会接受childView的请求的大小，然后通过childView的

Measure(newWidthMeasureSpec, heightMeasureSpec)函数存储到childView中，以便childView的getMeasuredWidth()

andgetMeasuredHeight() 的值可以被后续工作得到。

　　2.onLayout() 在这个函数中，ViewGroup会拿到childView的getMeasuredWidth() andgetMeasuredHeight()，用来布局所有的

childView。

　　3.View.MeasureSpec 与 LayoutParams 这两个类，是ViewGroup与childView协商大小用的。其中，View.MeasureSpec是

ViewGroup用来部署 childView用的， LayoutParams是childView告诉ViewGroup 我需要多大的地方。

　　4.在View 的onMeasure的最后要调用setMeasuredDimension()这个方法存储View的大小，这个方法决定了当前View的大小。

　　效果图：

原文：http://www.cnblogs.com/slider/archive/2011/11/24/2262161.html

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