Android 重写ViewGroup 分析onMeasure()和onLayout()方法

void android.view.View.setMeasuredDimension(int measuredWidth, int measuredHeight)

void android.view.View.measure(int widthMeasureSpec, int heightMeasureSpec)

void android.view.View.onMeasure(int widthMeasureSpec, int heightMeasureSpec)

void android.view.ViewGroup.onLayout(boolean changed, int l, int t, int r, int b)

android.view.View.MeasureSpec

package net.loonggg.viewgroup; 
 
import android.content.Context; 
import android.util.AttributeSet; 
import android.view.View; 
import android.view.ViewGroup; 
 
public class MyViewGroup extends ViewGroup { 
 
  public MyViewGroup(Context context) { 
    super(context); 
  } 
 
  public MyViewGroup(Context context, AttributeSet attrs) { 
    super(context, attrs); 
  } 
 
  public MyViewGroup(Context context, AttributeSet attrs, int defStyle) { 
    super(context, attrs, defStyle); 
  } 
 
  /** 
   * 计算控件的大小 
   */ 
  @Override 
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { 
    super.onMeasure(widthMeasureSpec, heightMeasureSpec); 
    int measureWidth = measureWidth(widthMeasureSpec); 
    int measureHeight = measureHeight(heightMeasureSpec); 
    // 计算自定义的ViewGroup中所有子控件的大小 
    measureChildren(widthMeasureSpec, heightMeasureSpec); 
    // 设置自定义的控件MyViewGroup的大小 
    setMeasuredDimension(measureWidth, measureHeight); 
  } 
 
  private int measureWidth(int pWidthMeasureSpec) { 
    int result = 0; 
    int widthMode = MeasureSpec.getMode(pWidthMeasureSpec);// 得到模式 
    int widthSize = MeasureSpec.getSize(pWidthMeasureSpec);// 得到尺寸 
 
    switch (widthMode) { 
    /** 
     * mode共有三种情况，取值分别为MeasureSpec.UNSPECIFIED, MeasureSpec.EXACTLY, 
     * MeasureSpec.AT_MOST。 
     * 
     * 
     * MeasureSpec.EXACTLY是精确尺寸， 
     * 当我们将控件的layout_width或layout_height指定为具体数值时如andorid 
     * :layout_width="50dip"，或者为FILL_PARENT是，都是控件大小已经确定的情况，都是精确尺寸。 
     * 
     * 
     * MeasureSpec.AT_MOST是最大尺寸， 
     * 当控件的layout_width或layout_height指定为WRAP_CONTENT时 
     * ，控件大小一般随着控件的子空间或内容进行变化，此时控件尺寸只要不超过父控件允许的最大尺寸即可 
     * 。因此，此时的mode是AT_MOST，size给出了父控件允许的最大尺寸。 
     * 
     * 
     * MeasureSpec.UNSPECIFIED是未指定尺寸，这种情况不多，一般都是父控件是AdapterView， 
     * 通过measure方法传入的模式。 
     */ 
    case MeasureSpec.AT_MOST: 
    case MeasureSpec.EXACTLY: 
      result = widthSize; 
      break; 
    } 
    return result; 
  } 
 
  private int measureHeight(int pHeightMeasureSpec) { 
    int result = 0; 
 
    int heightMode = MeasureSpec.getMode(pHeightMeasureSpec); 
    int heightSize = MeasureSpec.getSize(pHeightMeasureSpec); 
 
    switch (heightMode) { 
    case MeasureSpec.AT_MOST: 
    case MeasureSpec.EXACTLY: 
      result = heightSize; 
      break; 
    } 
    return result; 
  } 
 
  /** 
   * 覆写onLayout，其目的是为了指定视图的显示位置，方法执行的前后顺序是在onMeasure之后，因为视图肯定是只有知道大小的情况下， 
   * 才能确定怎么摆放 
   */ 
  @Override 
  protected void onLayout(boolean changed, int l, int t, int r, int b) { 
    // 记录总高度 
    int mTotalHeight = 0; 
    // 遍历所有子视图 
    int childCount = getChildCount(); 
    for (int i = 0; i < childCount; i++) { 
      View childView = getChildAt(i); 
 
      // 获取在onMeasure中计算的视图尺寸 
      int measureHeight = childView.getMeasuredHeight(); 
      int measuredWidth = childView.getMeasuredWidth(); 
 
      childView.layout(l, mTotalHeight, measuredWidth, mTotalHeight 
          + measureHeight); 
 
      mTotalHeight += measureHeight; 
 
    } 
  } 
 
} 

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
  xmlns:tools="http://schemas.android.com/tools" 
  android:layout_width="match_parent" 
  android:layout_height="match_parent" 
  android:background="#00f0f0" 
  tools:context=".MainActivity" > 
 
  <net.loonggg.viewgroup.MyViewGroup 
    android:id="@+id/myViewGroup" 
    android:layout_width="480dp" 
    android:layout_height="300dp" 
    android:background="#0f0f0f" > 
 
    <TextView 
      android:layout_width="200dp" 
      android:layout_height="100dp" 
      android:background="#000000" 
      android:gravity="center" 
      android:text="第一个TextView" /> 
 
    <TextView 
      android:layout_width="100dp" 
      android:layout_height="200dp" 
      android:background="#ffffff" 
      android:gravity="center" 
      android:text="第二个TextView" /> 
  </net.loonggg.viewgroup.MyViewGroup> 
 
</RelativeLayout> 

package net.loonggg.viewgroup; 
 
import android.os.Bundle; 
import android.app.Activity; 
 
public class MainActivity extends Activity { 
 
  @Override 
  protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
  } 
 
}