对于我的问题我准备了a very simple test app在 Github。

为简单起见，我删除了闪烁、滚动约束和边缘效果(它们在我的真实应用中运行良好):

所以 the custom view在我的测试应用中只支持滚动:

mGestureDetector = new GestureDetector(context,
        new GestureDetector.SimpleOnGestureListener() {
    @Override
    public boolean onScroll(MotionEvent e1, MotionEvent e2, float dX, float dY) {
        mBoardScrollX -= dX;
        mBoardScrollY -= dY;

        ViewCompat.postInvalidateOnAnimation(MyView.this);
        return true;
    }
});

并用 2 根手指捏合缩放(虽然焦点被打破了!):

mScaleDetector = new ScaleGestureDetector(context,
        new ScaleGestureDetector.SimpleOnScaleGestureListener() {
    @Override
    public boolean onScale(ScaleGestureDetector scaleDetector) {
        float focusX = scaleDetector.getFocusX();
        float focusY = scaleDetector.getFocusY();
        float factor = scaleDetector.getScaleFactor();

        mBoardScrollX = mBoardScrollX + focusX * (1 - factor) * mBoardScale;
        mBoardScrollY = mBoardScrollY + focusY * (1 - factor) * mBoardScale;
        mBoardScale *= factor;

        ViewCompat.postInvalidateOnAnimation(MyView.this);
        return true;
    }
});

最后，这里是绘制缩放和偏移游戏板的代码 Drawable:

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

    canvas.save();
    canvas.scale(mBoardScale, mBoardScale);
    canvas.translate(mBoardScrollX / mBoardScale, mBoardScrollY / mBoardScale);
    mBoard.draw(canvas);
    canvas.restore();
}

如果您尝试运行我的应用程序，您会注意到在使用两指缩放缩放手势缩放游戏板时，缩放焦点会跳来跳去。

我的理解是，在缩放 Drawable 时，我需要通过调整 mBoardScrollX 和 mBoardScrollY 值来平移它 - 以便焦点停留在游戏板坐标中的同一点。所以我的计算是 -

该点的旧位置是:

-mBoardScrollX + focusX * mBoardScale
-mBoardScrollY + focusY * mBoardScale

新的位置是:

-mBoardScrollX + focusX * mBoardScale * factor
-mBoardScrollY + focusY * mBoardScale * factor

通过求解这 2 个线性方程，我得到:

mBoardScrollX = mBoardScrollX + focusX * (1 - factor) * mBoardScale;
mBoardScrollY = mBoardScrollY + focusY * (1 - factor) * mBoardScale;

但是这不起作用!

为了消除任何错误，我什至尝试将焦点硬编码到自定义 View 的中间 - 但游戏板中心在缩放时仍然摇摆不定:

float focusX = getWidth() / 2f;
float focusY = getHeight() / 2f;

我想我遗漏了一些小东西，请帮助我。

我更愿意在不使用 Matrix 的情况下找到解决方案，因为我相信在上述计算中确实遗漏了一些非常小的东西。是的，我已经研究了很多可比较的代码，包括 PhotoView克里斯·贝恩斯 (Chris Banes) 和 InteractiveChart谷歌的例子。

双击更新:

pskink 基于 Matrix 的解决方案效果很好，但是我仍然有一个错误焦点的问题 -

我尝试将代码添加到 the custom view在双击手势上将缩放增加 100%:

public boolean onDoubleTap(final MotionEvent e) {
    float[] values = new float[9];
    mMatrix.getValues(values);
    float scale = values[Matrix.MSCALE_X];
    ValueAnimator animator = ValueAnimator.ofFloat(scale, 2f * scale);
    animator.setDuration(3000);
    animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
        @Override
        public void onAnimationUpdate(ValueAnimator animator){
            float scale = (float) animator.getAnimatedValue();
            mMatrix.setScale(scale, scale, e.getX(), e.getY());
            ViewCompat.postInvalidateOnAnimation(MyView.this);
        }
    });
    animator.start();
    return true;
}

虽然缩放正确更改，但焦点再次错误 - 即使焦点坐标已传递给每个 setScale 调用。

例如，当我在屏幕中间双击时，结果会向右和向下平移太远:

最佳答案

使用 Matrix 是一个真正更好的主意 - 代码更简单，您不必证明您的数学技能 ;-)，看看如何 Matrix使用了#postTranslate 和 Matrix#postScale 方法:

class MyView extends View {
    private static final String TAG = "MyView";

    private final ScaleGestureDetector mScaleDetector;
    private final GestureDetector mGestureDetector;

    private final Drawable mBoard;
    private final float mBoardWidth;
    private final float mBoardHeight;
    private Matrix mMatrix;

    public MyView(Context context) {
        this(context, null, 0);
    }

    public MyView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public MyView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);

        mBoard = ResourcesCompat.getDrawable(context.getResources(), R.drawable.chrome, null);
        mBoardWidth = mBoard.getIntrinsicWidth();
        mBoardHeight = mBoard.getIntrinsicHeight();
        mBoard.setBounds(0, 0, (int) mBoardWidth, (int) mBoardHeight);

        mMatrix = new Matrix();

        mScaleDetector = new ScaleGestureDetector(context, scaleListener);
        mGestureDetector = new GestureDetector(context, listener);
    }

    ScaleGestureDetector.OnScaleGestureListener scaleListener = new ScaleGestureDetector.SimpleOnScaleGestureListener() {
        @Override
        public boolean onScale(ScaleGestureDetector scaleDetector) {
            float factor = scaleDetector.getScaleFactor();
            mMatrix.postScale(factor, factor, getWidth() / 2f, getHeight() / 2f);
            ViewCompat.postInvalidateOnAnimation(MyView.this);
            return true;
        }
    };

    GestureDetector.OnGestureListener listener = new GestureDetector.SimpleOnGestureListener() {
        @Override
        public boolean onScroll(MotionEvent e1, MotionEvent e2, float dX, float dY) {
            mMatrix.postTranslate(-dX, -dY);
            ViewCompat.postInvalidateOnAnimation(MyView.this);
            return true;
        }
    };

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        float scale = Math.max(w / mBoardWidth, h / mBoardHeight);
        mMatrix.setScale(scale, scale);
        mMatrix.postTranslate((w - scale * mBoardWidth) / 2f, (h - scale * mBoardHeight) / 2f);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        canvas.save();
        canvas.concat(mMatrix);
        mBoard.draw(canvas);
        canvas.restore();
    }

    @Override
    @SuppressLint("ClickableViewAccessibility")
    public boolean onTouchEvent(MotionEvent e) {
        mGestureDetector.onTouchEvent(e);
        mScaleDetector.onTouchEvent(e);
        return true;
    }
}

关于android - 如何在自定义 View 中修复捏缩放焦点？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/55257981/