android佈局的學習（VG）

public class MyViewGroup extends ViewGroup {  
    public MyViewGroup(Context context) {  
        super(context);  
        this.initOtherComponent(context);  
    }  
    private void initOtherComponent(Context context) {  
        Button aBtn = new Button(context);  
        // set id 1  
        aBtn.setId(1);  
        aBtn.setText("a btn");  
        this.addView(aBtn);  
        Button bBtn = new Button(context);  
        // set id 2  
        bBtn.setId(2);  
        bBtn.setText("b btn");  
        this.addView(bBtn);  
    }  
    @Override  
    protected void onLayout(boolean changed, int l, int t, int r, int b) {  
        int childCount = getChildCount();  
        for (int i = 0; i < childCount; i++) {  
            View child = getChildAt(i);  
            switch (child.getId()) {  
            case 1:  
                // 1 is aBtn  
                Log.d("MyViewGroup", "btn1 setting"); 
                Log.d("MyViewGroup", "r="+r+":l"+l+":t"+t+":b"+b);  
                child.setVisibility(View.VISIBLE);  
                child.measure(r - l, b - t);//！！！！！
                child.layout(0, 0, child.getMeasuredWidth(), child  
                        .getMeasuredHeight());  
                break;  
            case 2:  
                // 2 is bBtn  
                Log.d("MyViewGroup", "btn2 setting");  
                child.setVisibility(View.VISIBLE);  
                child.measure(r - l, b - t);  
                child.layout(0, 50, child.getMeasuredWidth(), child.getMeasuredHeight() + 50);  
                break;  
            default:  
            }  
        }  
    }  
}