//ContextWrapper.java

public Intent registerReceiver(
    BroadcastReceiver receiver, IntentFilter filter) {
    return mBase.registerReceiver(receiver, filter);
}


//ContextImpl.java

private Intent registerReceiverInternal(BroadcastReceiver receiver, int userId,
        IntentFilter filter, String broadcastPermission,
        Handler scheduler, Context context, int flags) {
    IIntentReceiver rd = null;
    if (receiver != null) {
        if (mPackageInfo != null && context != null) {
            if (scheduler == null) {
                scheduler = mMainThread.getHandler();
            }
            //返回ReceiverDispatcher
            rd = mPackageInfo.getReceiverDispatcher(
                receiver, context, scheduler,
                mMainThread.getInstrumentation(), true);
        } else {
            if (scheduler == null) {
                scheduler = mMainThread.getHandler();
            }
            rd = new LoadedApk.ReceiverDispatcher(
                    receiver, context, scheduler, null, true).getIIntentReceiver();
        }
    }
    try {
    //ActivityManagerService注册
        final Intent intent = ActivityManager.getService().registerReceiver(
                mMainThread.getApplicationThread(), mBasePackageName, rd, filter,
                broadcastPermission, userId, flags);
        if (intent != null) {
            intent.setExtrasClassLoader(getClassLoader());
            intent.prepareToEnterProcess();
        }
        return intent;
    } catch (RemoteException e) {
        throw e.rethrowFromSystemServer();
    }
}

canvas.drawColor(Color.BLACK);
canvas.drawColor(Color.parse("#88880000"); // 半透明红色
canvas.drawRGB(100, 200, 100);
canvas.drawARGB(100, 100, 200, 100);

/**
前两个参数 centerX centerY 是圆心的坐标，第三个参数 radius 是圆的半径，单位都是像素
*/
drawCircle(float centerX, float centerY, float radius, Paint paint) 

canvas.drawCircle(300, 300, 200, paint);