在父边界内限制子视图

Question

我正在创建一个矩形框并在其中放置一个可以移动的imageView.在做onMove的时候,我注意到imageView已经超出了我不想要的父视图的边界.我想在它的父视图的边界内限制imageView.怎么做.

这是xml:

<FrameLayout
    android:layout_width="400dp"
    android:layout_height="400dp"
    android:layout_centerHorizontal="true"
    android:layout_centerVertical="true"
    android:id="@+id/objContainer"
    android:background="@android:color/holo_blue_bright" >
 <ImageView
        android:id="@+id/iv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:src="@android:drawable/btn_default" />
</FrameLayout>

</RelativeLayout>

和handletouch事件的代码:

@Override
public boolean onTouch(View view, MotionEvent event) {
    switch (event.getAction() & MotionEvent.ACTION_MASK) {
        case MotionEvent.ACTION_DOWN:
            final float x = event.getRawX();
            final float y = event.getRawY();

            // Remember where we started
            mLastTouchX = x;
            mLastTouchY = y;

            break;
        case MotionEvent.ACTION_UP:
            break;
        case MotionEvent.ACTION_POINTER_DOWN:
            break;
        case MotionEvent.ACTION_POINTER_UP:
            break;
        case MotionEvent.ACTION_MOVE:


            final float x1 = event.getRawX();
            final float y1 = event.getRawY();

            // Calculate the distance moved
            final float dx = x1 - mLastTouchX;
            final float dy = y1 - mLastTouchY;

            // Move the object
            mPosX += dx;
            mPosY += dy;
            view.setX(mPosX);
            view.setY(mPosY);

            // Remember this touch position for the next move event
            mLastTouchX = x1;
            mLastTouchY = y1;

            // Invalidate to request a redraw
            root.invalidate();
            break;
    }
    return true;
}}

Answer 1

在被覆盖的内部,您onTouch需要检查以下移动是否会保留ImageView其容器内部.

换句话说,你需要检查ImageViewdx,dy移动后矩形是否会留在父级内部.

这是一个例子:

case MotionEvent.ACTION_MOVE:
    ...
    // Calculate the distance moved
    final float dx = x1 - mLastTouchX;
    final float dy = y1 - mLastTouchY;

    // Make sure we will still be the in parent's container
    Rect parent = new Rect(0, 0, root.getWidth(), root.getHeight());

    int newLeft = (int) (iv.getX() + dx),
            newTop = (int) (iv.getY() + dy),
            newRight = newLeft + iv.getWidth(),
            newBottom = newTop + iv.getHeight();

    if (!parent.contains(newLeft, newTop, newRight, newBottom)) {
        Log.e(TAG, String.format("OOB @ %d, %d - %d, %d",
                newLeft, newTop, newRight, newBottom));
        break;
    }
    ...

另请注意,您不需要使容器无效,因为setX/setY使ImageView自身无效.