自定义view(四)覆写onLayout进行layout，含自定义ViewGroup

本文转自http://blog.csdn.net/androiddevelop/article/details/8108970
视图的绘制仅在Framework层分为三个阶段measure，layout，draw。前一篇博文《 覆写onMeaure进行measure操作》
关于如何覆写onMeasure， 其目的是为了测量视图的大小也就是第一阶段，如果不了解或者关于onMeasure有什么疑惑可以了解下。 本篇博文是关于如何覆写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。

一、自定义ViewGroup例子

例子代码 - 纵向显示两个TextView

（1）编写CustomViewGroup

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1. CustomViewGroup继承自ViewGroup，ViewGroup是所有Layout的父类

public class CustomViewGroup extends ViewGroup {

}

2. 覆写View.onMeasure回调函数，用于计算所有child view的宽高，这里偷懒没有进行MeasureSpec模式判断

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@Override

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

int widthSize = MeasureSpec.getSize(widthMeasureSpec);

int heightSize = MeasureSpec.getSize(heightMeasureSpec);

measureChildren(widthMeasureSpec, heightMeasureSpec);

setMeasuredDimension(widthSize, heightSize);

}

3. 覆写ViewGroup.onLayout回调函数，用于指定所有child View的位置

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@Override

protected void onLayout(boolean changed, int left, int top, int right, int bottom) {

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(left, mTotalHeight, measuredWidth, mTotalHeight + measureHeight);

mTotalHeight += measureHeight;

Log.e(TAG, "changed = " + changed

+ ", left = " + left + ", top = " + top

+ ", right = " + right + ", bottom = " + bottom

+ ", measureWidth = " + measuredWidth + ", measureHieght = " + measureHeight);

}

}

3.1 onLayout回调函数参数：
left, top, right, bottom是当前ViewGroup整个在屏幕上的位置，手机屏幕是480 * 800 ，其中高度去除状态栏和title大概724
如果页面只有此ViewGroup则个参数的值

left = 0, top = 0, right = 480, bottom = 724



在此ViewGroup的上面放置一个TextView当期回调的参数值
left = 0, top = 25, right = 480, bottom = 724



3.2 child.layout如何填写参数
View是一个矩形，right和bottom也可以通过以下计算获得，其中Width 和 Height由onMeasure最终设置和决定

right = left + width

bottom = top + height

（2）创建Activity

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public class CustomViewGroupActivity extends Activity {

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

CustomViewGroup customViewGroup = new CustomViewGroup(this);

customViewGroup.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT));

// 添加子视图

TextView textViewOne = new TextView(this);

textViewOne.setText("a child view");

textViewOne.setBackgroundColor(Color.BLUE);

textViewOne.setLayoutParams(new LayoutParams(130, 130));

customViewGroup.addView(textViewOne);

TextView textViewTwo = new TextView(this);

textViewTwo.setText("b child view");

textViewTwo.setBackgroundColor(Color.RED);

textViewTwo.setLayoutParams(new LayoutParams(80, 80));

customViewGroup.addView(textViewTwo);

setContentView(customViewGroup);

}

}

二 、扩展

× 三个方法的区别？后这个方法最终还是调用第一个方法

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childView.measure(widthMeasureSpec, heightMeasureSpec);

measureChild(childView, widthMeasureSpec, heightMeasureSpec);

measureChildren(widthMeasureSpec, heightMeasureSpec);

× 哪些视图属性影响 measure？ padding、margin

× 哪些视图属性 影响 layout？ gravity

× view的上下左右和measurespec width和height的关系 ？

三、资料
Android官方文档：
Layouts
http://developer.android.com/guide/topics/ui/declaring-layout.html

细说view流程上
/article/1382125.html
细说view流程下
/article/1382124.html

2013-03-31 更新与onMeasure关联博文
2013-06-20 xiaoxia19920920 兄帮助解决一个疑惑，代码与xml设置大小的不同。一个单位是px一个是dip。