未解决问题

@、

1、自定义了一个RelativeLayout类MyCustomLayout，然后在onDraw(...)中，画一个圆canvas.drawCircle(...)。

2、自定义了一个Dialog类MyDialog，其中xml中是RelativeLayout，并且layout_height和layout_width都是match_parent，然后在onCreate(...)中，创建一个MyCustomLayout。

3、在MainActivity中创建MyDialog，然后show。

问题：

1、为什么在MyCustomLayout的构造函数中调用了setBackgroundColor(...)，画的圆才能显示。

2、为什么在MyDialog.onCreate()中创建MyCustomLayout变量的LayoutParams不能设置为wrap_conent。

代码：

public class MyCustomLayout extends RelativeLayout {
    private static final String TAG = "My--CustomView";

    private int mRadius = 5;

    public MyCustomLayout(Context context) {
        super(context);
        Log.d(TAG, "Constructor1");
        // Why have to call this ??
        setBackgroundColor(getResources().getColor(
                android.R.color.transparent));
    }

    public MyCustomLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
        Log.d(TAG, "Constructor2");
        setBackgroundColor(getResources().getColor(
                android.R.color.transparent));
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

//        canvas.drawColor(Color.parseColor("#000000"));
        Paint paint = new Paint();
        paint.setAntiAlias(true);
        paint.setColor(Color.parseColor("#FFFF00"));
        Log.d(TAG, getWidth() + " -- " + getHeight() + " -- " + Utils.dpToPx(mRadius, getResources()));
        canvas.drawCircle(getWidth() / 2, getHeight() / 2, Utils.dpToPx(mRadius, getResources()), paint);
    }

    public int getRadius() {
        return mRadius;
    }

    public void setRadius(int radius) {
        mRadius = radius;
        invalidate();
    }
}

class MyDialog extends Dialog {
       MyCustomLayout mMyCustomLayout;

        public MyDialog(Context context) {
            super(context, android.R.style.Theme_Translucent);
        }

        @Override
        public void show() {
            super.show();
            Log.d("MyDialog", "show");
        }

        @Override
        public void dismiss() {
            super.dismiss();
            Log.d("MyDialog", "dismiss");
//            mMyCustomView.setRadius(0);
        }

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            requestWindowFeature(Window.FEATURE_NO_TITLE);
            super.onCreate(savedInstanceState);
            setContentView(R.layout.my_dialog);

            Log.d("MyDialog", "onCreate");

            RelativeLayout content = (RelativeLayout) this
                    .findViewById(R.id.my_custom_view_content);
            mMyCustomLayout = new MyCustomLayout(this.getContext());
            content.addView(mMyCustomLayout);

            mMyCustomLayout.setLayoutParams(
                    new RelativeLayout.LayoutParams(
                            RelativeLayout.LayoutParams.FILL_PARENT,
                    RelativeLayout.LayoutParams.FILL_PARENT));
        }
    }

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                android:id="@+id/my_custom_view_content"
                android:layout_width="match_parent"
                android:layout_height="match_parent">
 </RelativeLayout>