安卓问题 : View with endless scrolling

Question

我有一个实现了滚动的自定义 View ，但它似乎在图像上无休止地滚动。
即使我找到图像的边缘，它也会一直滚动到空白背景。

我不能使用 WebView，因为我还有一些 Canvas sutff。
有谁知道如何为这个问题设置限制？
滚动时如何调整图片的边缘？


编辑:我在@JosephEarl 的帮助下找到了最佳解决方案。
我只设置了左边界和上边界，因为我的图像比屏幕大。
此外，我在使用缩放功能时关闭边界，否则我无法再移动它。

1) 在 onTouch 事件的 ACTION_MOVE 情况下，插入此代码:

if(!isZoomed) {
    if(mPosX < 0)
        mPosX = 0;
    else if(mPosX > mWidth)
        mPosX = mWidth;
    if(mPosY < 0)
        mPosY = 0;
    else if(mPosY > mHeight)
        mPosY = mHeight;
}

2) 在使用缩放时打开或关闭边界。
将以下代码添加到您的 ACTION_POINTER_UP 案例中:

case MotionEvent.ACTION_POINTER_UP: {

    final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
    final int pointerId = ev.getPointerId(pointerIndex);

    if (pointerId == mActivePointerId) {
        final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
        mLastTouchX = ev.getX(newPointerIndex);
        mLastTouchY = ev.getY(newPointerIndex);
        mActivePointerId = ev.getPointerId(newPointerIndex);
        isZoomed = true;

    } else
        isZoomed = false;

    break;

}

就这样。
以下是所有相关方法和完整的 onTouch 事件:

private float scaleFactor = 1.f;
private ScaleGestureDetector detector;

private static final int INVALID_POINTER_ID = -1;
private int mActivePointerId = INVALID_POINTER_ID;

private float mPosX;
private float mPosY;
private float mLastTouchX;
private float mLastTouchY;

private float mWidth;
private float mHeight;
private boolean isZoomed = false;

// OTHER CODE GOES HERE

@Override
public boolean onTouchEvent(MotionEvent ev) {
    detector.onTouchEvent(ev);

    final int action = ev.getAction();
    switch (action & MotionEvent.ACTION_MASK) {
        case MotionEvent.ACTION_DOWN: {
            final float x = ev.getX();
            final float y = ev.getY();

            mLastTouchX = x;
            mLastTouchY = y;
            mActivePointerId = ev.getPointerId(0);
            break;
        }

        case MotionEvent.ACTION_MOVE: {
            final int pointerIndex = ev.findPointerIndex(mActivePointerId);
            final float x = ev.getX(pointerIndex);
            final float y = ev.getY(pointerIndex);

            if (!detector.isInProgress()) {
                final float dx = x - mLastTouchX;
                final float dy = y - mLastTouchY;
                mPosX += dx;
                mPosY += dy;

                if(!isZoomed) {
                    if(mPosX < 0)
                        mPosX = 0;
                    else if(mPosX > mWidth)
                        mPosX = mWidth;
                    if(mPosY < 0)
                        mPosY = 0;
                    else if(mPosY > mHeight)
                        mPosY = mHeight;
                }

                invalidate();
            }

            mLastTouchX = x;
            mLastTouchY = y;

            break;
        }

        case MotionEvent.ACTION_UP: {
            mActivePointerId = INVALID_POINTER_ID;
            break;
        }

        case MotionEvent.ACTION_CANCEL: {
            mActivePointerId = INVALID_POINTER_ID;
            break;
        }

        case MotionEvent.ACTION_POINTER_UP: {

            final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
            final int pointerId = ev.getPointerId(pointerIndex);

            if (pointerId == mActivePointerId) {
                final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
                mLastTouchX = ev.getX(newPointerIndex);
                mLastTouchY = ev.getY(newPointerIndex);
                mActivePointerId = ev.getPointerId(newPointerIndex);
                isZoomed = true;

            } else
                isZoomed = false;

            break;

        }
    }

    return true;
}

private class ScaleListener extends
        ScaleGestureDetector.SimpleOnScaleGestureListener {
    @Override
    public boolean onScale(ScaleGestureDetector detector) {
        scaleFactor *= detector.getScaleFactor();
        scaleFactor = Math.max(MIN_ZOOM, Math.min(scaleFactor, MAX_ZOOM));
        invalidate();
        return true;
    }
}

@Override
protected void onSizeChanged(int xNew, int yNew, int xOld, int yOld){
     super.onSizeChanged(xNew, yNew, xOld, yOld);
     mWidth = xNew;
     mHeight = yNew;
}

// OTHER CODE GOES HERE

Answer 1

从您的代码看来，您绝不会尝试检测可滚动区域的大小并将位置限制在这些范围内，即您应该检查以确保 mPosX 和 mPosY 不要超出他们的界限。

系统不会自动限制你自定义View的位置，需要你自己做。

顶部和左侧边界将为 0、0——您应确保 mPosX 和 mPosY 不大于此值。

右边界将是(容器 View 的宽度 - ScrollView 的宽度)——这应该是负数(如果它大于则将右边界设置为 0)并且你应该确保 mPosX 不少于此。底部边界将是(容器的高度 - ScrollView 的高度)——这又应该是负数，您应该确保 mPosY 不小于该值。

总结一下，当触摸事件开始时计算边界:

// Calculate our bounds.
int leftBound = 0;
int topBound = 0;
int rightBound = imageWidth - getWidth();
if (rightBound > 0) {
    rightBound = 0;
}
int bottomBound = imageHeight - getHeight();
if (bottomBound > 0) {
    bottomBound = 0;
}

imageWidth 和 imageHeight 是您正在滚动的内容的宽度和高度。

然后在滚动时确保遵守边界:

if (mPosX > leftBound) {
    mPosX = leftBound;
} else if (mPosX < rightBound) {
    mPosX = rightBound;
}

if (mPosY > topBound) {
    mPosY = topBound;
} else if (mPosY < bottomBound) {
    mPosY = bottomBound;
}