安卓实现双指滑动图片放大缩小，单指滑动图片移动,双击图片放大，再一次双击图片复原

实现双指滑动图片放大缩小，单指滑动图片移动，双击图片放大，再一次双击图片复原的效果，可以通过以下步骤实现：

1. 在布局文件中添加一个 ImageView，设置其初识状态为居中显示一张图片。

2. 在代码中获取该 ImageView，并设置其可缩放、可拖动。

3. 通过 GestureDetector 监听用户手势操作，判断用户是单指还是双指操作，并做出相应的处理。

4. 对于双指操作，可以通过 ScaleGestureDetector 监听缩放比例的变化，从而实现图片的放大缩小。

5. 对于单指操作，可以通过手势监听器中的 onTouchEvent 方法来处理图片的移动。

6. 对于双击操作，可以通过 GestureDetector 中的 onDoubleTap 方法来实现图片的放大和复原。

以下是一个简单的实现代码示例：

public class MainActivity extends AppCompatActivity {

    private ImageView mImageView;
    private float mScaleFactor = 1.0f;
    private float mLastTouchX, mLastTouchY;
    private int mActivePointerId = -1;
    private ScaleGestureDetector mScaleGestureDetector;
    private GestureDetector mGestureDetector;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mImageView = findViewById(R.id.imageView);
        mScaleGestureDetector = new ScaleGestureDetector(this, new ScaleListener());
        mGestureDetector = new GestureDetector(this, new GestureListener());

        // 设置图片可缩放、可拖动
        mImageView.setScaleType(ImageView.ScaleType.MATRIX);
        mImageView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                mScaleGestureDetector.onTouchEvent(event);
                mGestureDetector.onTouchEvent(event);

                final int action = event.getAction();
                switch (action & MotionEvent.ACTION_MASK) {
                    case MotionEvent.ACTION_DOWN: {
                        final float x = event.getX();
                        final float y = event.getY();
                        mLastTouchX = x;
                        mLastTouchY = y;
                        mActivePointerId = event.getPointerId(0);
                        break;
                    }
                    case MotionEvent.ACTION_MOVE: {
                        final int pointerIndex = event.findPointerIndex(mActivePointerId);
                        final float x = event.getX(pointerIndex);
                        final float y = event.getY(pointerIndex);
                        if (!mScaleGestureDetector.isInProgress()) {
                            final float dx = x - mLastTouchX;
                            final float dy = y - mLastTouchY;
                            mImageView.postTranslate(dx, dy);
                        }
                        mLastTouchX = x;
                        mLastTouchY = y;
                        break;
                    }
                    case MotionEvent.ACTION_UP: {
                        mActivePointerId = -1;
                        break;
                    }
                    case MotionEvent.ACTION_CANCEL: {
                        mActivePointerId = -1;
                        break;
                    }
                    case MotionEvent.ACTION_POINTER_UP: {
                        final int pointerIndex = (event.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
                        final int pointerId = event.getPointerId(pointerIndex);
                        if (pointerId == mActivePointerId) {
                            final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
                            mLastTouchX = event.getX(newPointerIndex);
                            mLastTouchY = event.getY(newPointerIndex);
                            mActivePointerId = event.getPointerId(newPointerIndex);
                        }
                        break;
                    }
                }

                mImageView.invalidate();
                return true;
            }
        });
    }

    private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {
        @Override
        public boolean onScale(ScaleGestureDetector detector) {
            mScaleFactor *= detector.getScaleFactor();
            mScaleFactor = Math.max(0.1f, Math.min(mScaleFactor, 10.0f));

            mImageView.setScaleX(mScaleFactor);
            mImageView.setScaleY(mScaleFactor);

            return true;
        }
    }

    private class GestureListener extends GestureDetector.SimpleOnGestureListener {
        @Override
        public boolean onDoubleTap(MotionEvent e) {
            if (mScaleFactor == 1.0f) {
                mScaleFactor = 2.0f;
            } else {
                mScaleFactor = 1.0f;
            }

            mImageView.setScaleX(mScaleFactor);
            mImageView.setScaleY(mScaleFactor);

            return true;
        }
    }
}