正好Philm项目中使用到了PhotoView,借此机会深入了解PhotoView的源码，PhotoView是一个非常好的图片显示第三方开源库，支持手势缩放移动图片等操作。PhotoView源码可在github上下载，下载链接PhotoView

重要的类和字段功能

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PhotoView extends ImageView
	内部强制将ImageView的scaletype保持为matrix，在xml中设置不生效，可以通过设置setScaleType，修改PhotoViewAttacher的scaleType，从而达到需要的效果
    PhotoViewAttacher：PhoneView的几乎所有功能实现类
        mBaseRotation：图片默认旋转角，mSuppMatrix会默认postRotation(mBaseRotation)
        mBaseMatrix ：根据imaegview scaleType来生成，即控制drawable instinct width/height到imageview width/height的矩阵，
        生成baseMatrix的代码非常有意思，下面将baseMatrix的生成代码贴了出来
        mSuppMatrix：对应用户手势变化的矩阵
        mDrawMatrix：mSuppMatrix*mBaseMatrix
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//BaseMatrix举证的生成代码
private void updateBaseMatrix(Drawable d) {
        ImageView imageView = getImageView();
        if (null == imageView || null == d) {
            return;
        }
        final float viewWidth = getImageViewWidth(imageView);
        final float viewHeight = getImageViewHeight(imageView);
        final int drawableWidth = d.getIntrinsicWidth();
        final int drawableHeight = d.getIntrinsicHeight();
        mBaseMatrix.reset();
        final float widthScale = viewWidth / drawableWidth;
        final float heightScale = viewHeight / drawableHeight;
        if (mScaleType == ScaleType.CENTER) {
            mBaseMatrix.postTranslate((viewWidth - drawableWidth) / 2F,
                    (viewHeight - drawableHeight) / 2F);
        } else if (mScaleType == ScaleType.CENTER_CROP) {
            float scale = Math.max(widthScale, heightScale);
            mBaseMatrix.postScale(scale, scale);
            mBaseMatrix.postTranslate((viewWidth - drawableWidth * scale) / 2F,
                    (viewHeight - drawableHeight * scale) / 2F);
        } else if (mScaleType == ScaleType.CENTER_INSIDE) {
            float scale = Math.min(1.0f, Math.min(widthScale, heightScale));
            mBaseMatrix.postScale(scale, scale);
            mBaseMatrix.postTranslate((viewWidth - drawableWidth * scale) / 2F,
                    (viewHeight - drawableHeight * scale) / 2F);
        } else {
            RectF mTempSrc = new RectF(0, 0, drawableWidth, drawableHeight);
            RectF mTempDst = new RectF(0, 0, viewWidth, viewHeight);
            if ((int) mBaseRotation % 180 != 0) {
                mTempSrc = new RectF(0, 0, drawableHeight, drawableWidth);
            }
            switch (mScaleType) {
                case FIT_CENTER:
                    mBaseMatrix
                            .setRectToRect(mTempSrc, mTempDst, ScaleToFit.CENTER);
                    break;
                case FIT_START:
                    mBaseMatrix.setRectToRect(mTempSrc, mTempDst, ScaleToFit.START);
                    break;
                case FIT_END:
                    mBaseMatrix.setRectToRect(mTempSrc, mTempDst, ScaleToFit.END);
                    break;
                case FIT_XY:
                    mBaseMatrix.setRectToRect(mTempSrc, mTempDst, ScaleToFit.FILL);
                    break;
                default:
                    break;
            }
        }
        resetMatrix();
    }

学习知识点

onTouch ACTION_DOWN时

通过parent.requestDisallowInterceptTouchEvent(true)阻止parent劫持事件

matrix的scale获取方法：

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(float) Math.sqrt((float) Math.pow(getValue(mSuppMatrix, Matrix.MSCALE_X), 2) + (float) Math.pow(getValue(mSuppMatrix, Matrix.MSKEW_Y), 2));

GestureDetector.OnDoubleTapListener

通过该listener可以监听onSingleTapConfirmed, onDoubleTap

GestureDetector.SimpleOnGestureListener

通过该listener可以监听onLongPress， onFling

ScaleGestureDetector.OnScaleGestureListener

通过该listener可以监听onScale，onScaleBegin，onScaleEnd

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ScaleGestureDetector.OnScaleGestureListener mScaleListener = new ScaleGestureDetector.OnScaleGestureListener() {
    @Override
    public boolean onScale(ScaleGestureDetector detector) {
        float scaleFactor = detector.getScaleFactor();
        if (Float.isNaN(scaleFactor) || Float.isInfinite(scaleFactor))
            return false;
        mListener.onScale(scaleFactor,
            detector.getFocusX(), detector.getFocusY());
        return true;
    }
    @Override
    public boolean onScaleBegin(ScaleGestureDetector detector) {
        return true;
    }
    @Override
    public void onScaleEnd(ScaleGestureDetector detector) {
        // NO-OP
    }
};
mDetector = new ScaleGestureDetector(context, mScaleListener);

VelocityTracker

通过VelocityTracker可以检测fling的速度，重要接口如下：

  • mVelocityTracker.addMovement(ev);
  • mVelocityTracker.recycle()
  • mVelocityTracker.computeCurrentVelocity(1000);
  • mVelocityTracker.getXVelocity()
  • mVelocityTracker.getXVelocity()

OverScroller

通过OverScroller可以控制fling，重要接口如下：

  • mScroller.computeScrollOffset()
  • mScroller.fling(startX, startY, velocityX, velocityY, minX, maxX, minY, maxY, overX, overY)
  • mScroller.isFinished()
  • mScroller.getCurrX()
  • mScroller.getCurrY()