如何在 Android imageView 中限制图像平移边界

Question

我有一个大致基于this tutorial 的多点触控图像视图。那里的一位评论者提出了一种半脏方法，将图像拖动限制在图像的边界内，使图像边缘不能被拖动到其边缘之外。这种方法有点工作，但不是完全有效。它只限制两条边的拖动。

有谁知道限制图像拖动的不那么凌乱且实用的方法？

对于 Android 应用程序开发来说，这是一个非常重要的概念，但没有得到充分的解决......

我想到了以下想法：

1) setScaleType(scaleType.fitXY) 当 zoom = 1.0F（即最小缩放）时，只有在 zoom > 1.0f 时才启用拖动

2) 当缩放 > 1.0f 时，setScaleType(scaleType.MATRIX)，然后您确定图像边界和屏幕尺寸，并且以某种方式对我来说太聪明了，使用 if 语句您只允许在图像边缘拖动不在屏幕上。我不知道如何声明，就是这样。

无论如何，为了完整起见，这里是来自该链接的限制平移代码。这似乎是 stackoverflow 上最受欢迎的建议，但我认为我们可以做得更好：

// limit pan
matrix.getValues(matrixValues);
float currentY = matrixValues[Matrix.MTRANS_Y];
float currentX = matrixValues[Matrix.MTRANS_X];
float currentScale = matrixValues[Matrix.MSCALE_X];
float currentHeight = height * currentScale;
float currentWidth = width * currentScale;
float dx = event.getX() - start.x;
float dy = event.getY() - start.y;
float newX = currentX+dx;
float newY = currentY+dy; 

RectF drawingRect = new RectF(newX, newY, newX+currentWidth, newY+currentHeight);
float diffUp = Math.min(viewRect.bottom-drawingRect.bottom, viewRect.top-drawingRect.top);
float diffDown = Math.max(viewRect.bottom-drawingRect.bottom, viewRect.top-drawingRect.top);
float diffLeft = Math.min(viewRect.left-drawingRect.left, viewRect.right-drawingRect.right);
float diffRight = Math.max(viewRect.left-drawingRect.left, viewRect.right-drawingRect.right);
if(diffUp > 0 ){
dy +=diffUp; 
}
if(diffDown < 0){
dy +=diffDown;
} 
if( diffLeft> 0){ 
dx += diffLeft;
}
if(diffRight < 0){
dx += diffRight;
}
matrix.postTranslate(dx, dy);

Answer 1

private void limitDrag(Matrix m, ImageView view) {


    float[] values = new float[9];
    m.getValues(values);
    float transX = values[Matrix.MTRANS_X];
    float transY = values[Matrix.MTRANS_Y];
    float scaleX = values[Matrix.MSCALE_X];
    float scaleY = values[Matrix.MSCALE_Y];

    Rect bounds = view.getDrawable().getBounds();
    int viewWidth = getResources().getDisplayMetrics().widthPixels;
    int viewHeight = getResources().getDisplayMetrics().heightPixels;



    if(viewHeight<=480)
    {

        _y_up=0;
    }
    if(viewHeight>480&&viewHeight<980)
    {

        _y_up=140;
    }

    int width = bounds.right - bounds.left;
    int height = bounds.bottom - bounds.top;
    int __width=width;
    int __height=height;
    width = viewWidth / 2;
    height = viewHeight / 2;


    //height = 200 ;
    float minX = (-width) ;//* scaleX;
    float minY = (-height) ;//* scaleY;


    if ((transX) > (viewWidth)) {

        //_x_left

        transX = viewWidth;
    } else if (transX < minX) {


        transX = minX;
    }


    if ((-transX) > (viewWidth)) {
             // _x_right
        transX = -(viewWidth);
    } else if (-transX < minX) {

        transX = -(minX+30);
    }



    if ((transY) > (viewHeight)) {
    //  _y_up
        transY =( viewHeight);


    } else if (transY < minY) {

        transY = (minY+_y_up);
    }

    if ((-transY) > (viewHeight)) {
    //  _y_down
        transY = -(viewHeight);

    } else if (-transY < minY) {

        transY = -(minY+170);
    }

    values[Matrix.MTRANS_X] = transX;
    values[Matrix.MTRANS_Y] = transY;
    m.setValues(values);
}

在你的 view.setImageMatrix(matrix) 上面调用它；

Answer 2

我意识到这已经很老了，但是试试这个。 imageWidth 和 imageHeight 是未缩放的值。

private void limitDrag(Matrix m, ImageView view, int imageWidth, int imageHeight) {
    float[] values = new float[9];
    m.getValues(values);
    float[] orig = new float[] {0,0, imageWidth, imageHeight};
    float[] trans = new float[4];
    m.mapPoints(trans, orig);

    float transLeft = trans[0];
    float transTop = trans[1];
    float transRight = trans[2];
    float transBottom = trans[3];
    float transWidth = transRight - transLeft;
    float transHeight = transBottom - transTop;

    float xOffset = 0;
    if (transWidth > view.getWidth()) {
        if (transLeft > 0) {
            xOffset = -transLeft;
        } else if (transRight < view.getWidth()) {
            xOffset = view.getWidth() - transRight;
        }
    } else {
        if (transLeft < 0) {
            xOffset = -transLeft;
        } else if (transRight > view.getWidth()) {
            xOffset = -(transRight - view.getWidth());
        }
    }

    float yOffset = 0;
    if (transHeight > view.getHeight()) {
        if (transTop > 0) {
            yOffset = -transTop;
        } else if (transBottom < view.getHeight()) {
            yOffset = view.getHeight() - transBottom;
        }
    } else {
        if (transTop < 0) {
            yOffset = -transTop;
        } else if (transBottom > view.getHeight()) {
            yOffset = -(transBottom - view.getHeight());
        }
    }

    float transX = values[Matrix.MTRANS_X];
    float transY = values[Matrix.MTRANS_Y];

    values[Matrix.MTRANS_X] = transX + xOffset;
    values[Matrix.MTRANS_Y] = transY + yOffset;
    m.setValues(values);
}