View的onDraw函數不被調用

1.要實現一個容器  如此做：

public class CustomFrameLayout extends FrameLayout {private static final String TAG = "CustomFrameLayout";public CustomFrameLayout(Context context) {super(context);this.setWillNotDraw(false);//必須}public void onDraw(Canvas canvas){super.onDraw(canvas);drawSomething(canvas);}}

建構函式中沒有this.setWillNotDraw(false)這句話時候onDraw函數始終不被調用
直到添加上之後才可以成功調用onDraw函數

仔細查看onDraw函數的說明：

public void setWillNotDraw (boolean willNotDraw)Since: API Level 1

If this view doesn't do any drawing on its own, set this flag to allow further optimizations. By default, this flag is not set on View, but could be set on some View subclasses such as ViewGroup. Typically, if you overrideonDraw(Canvas) you
should clear this flag.

Parameters

willNotDraw	whether or not this View draw on its own

總之，要想再自訂的畫一些東西 就要進行setWillNotDraw(false).2.如果你有兩個容器 A 和 a，a是放在A之中。如果都對這兩個容器設定了setWillNotDraw(false)，那麼你將會看到一個“奇蹟"：a中被添加進來的控制項都不透明了，這時候不要懷疑你的控制項圖片不是透明的，是因為你對A容器設定了setWillNotDraw(false)，嘗試將其去掉，問題就OK了