[Android 机制] 如何实现手势缩放图片

import android.graphics.Matrix;
import android.graphics.PointF;
import android.util.FloatMath;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.ImageView;

public class MulitPointTouchListener implements OnTouchListener {
        private static final String TAG = "Touch";
        // These matrices will be used to move and zoom image
        Matrix matrix = new Matrix();
        Matrix savedMatrix = new Matrix();

        // We can be in one of these 3 states
        static final int NONE = 0;
        static final int DRAG = 1;
        static final int ZOOM = 2;
        int mode = NONE;

        // Remember some things for zooming
        PointF start = new PointF();
        PointF mid = new PointF();
        float oldDist = 1f;

        @Override
        public boolean onTouch(View v, MotionEvent event) {

                ImageView view = (ImageView) v;
                // Log.e("view_width",
                // view.getImageMatrix()..toString()+"*"+v.getWidth());
                // Dump touch event to log
                dumpEvent(event);

                // Handle touch events here...
                switch (event.getAction() & MotionEvent.ACTION_MASK) {
                case MotionEvent.ACTION_DOWN:

                        matrix.set(view.getImageMatrix());
                        savedMatrix.set(matrix);
                        start.set(event.getX(), event.getY());
                        //Log.d(TAG, "mode=DRAG");
                        mode = DRAG;

                       
                        //Log.d(TAG, "mode=NONE");
                        break;
                case MotionEvent.ACTION_POINTER_DOWN:
                        oldDist = spacing(event);
                        //Log.d(TAG, "oldDist=" + oldDist);
                        if (oldDist > 10f) {
                                savedMatrix.set(matrix);
                                midPoint(mid, event);
                                mode = ZOOM;
                                //Log.d(TAG, "mode=ZOOM");
                        }
                        break;
                case MotionEvent.ACTION_UP:
                case MotionEvent.ACTION_POINTER_UP:
                        mode = NONE;
                        //Log.e("view.getWidth", view.getWidth() + "");
                        //Log.e("view.getHeight", view.getHeight() + "");

                        break;
                case MotionEvent.ACTION_MOVE:
                        if (mode == DRAG) {
                                // ...
                                matrix.set(savedMatrix);
                                matrix.postTranslate(event.getX() - start.x, event.getY()
                                                - start.y);
                        } else if (mode == ZOOM) {
                                float newDist = spacing(event);
                                //Log.d(TAG, "newDist=" + newDist);
                                if (newDist > 10f) {
                                        matrix.set(savedMatrix);
                                        float scale = newDist / oldDist;
                                        matrix.postScale(scale, scale, mid.x, mid.y);
                                }
                        }
                        break;
                }

                view.setImageMatrix(matrix);
                return true; // indicate event was handled
        }

        private void dumpEvent(MotionEvent event) {
                String names[] = { "DOWN", "UP", "MOVE", "CANCEL", "OUTSIDE",
                                "POINTER_DOWN", "POINTER_UP", "7?", "8?", "9?" };
                StringBuilder sb = new StringBuilder();
                int action = event.getAction();
                int actionCode = action & MotionEvent.ACTION_MASK;
                sb.append("event ACTION_").append(names[actionCode]);
                if (actionCode == MotionEvent.ACTION_POINTER_DOWN
                                || actionCode == MotionEvent.ACTION_POINTER_UP) {
                        sb.append("(pid ").append(
                                        action >> MotionEvent.ACTION_POINTER_ID_SHIFT);
                        sb.append(")");
                }
                sb.append("[");
                for (int i = 0; i < event.getPointerCount(); i++) {
                        sb.append("#").append(i);
                        sb.append("(pid ").append(event.getPointerId(i));
                        sb.append(")=").append((int) event.getX(i));
                        sb.append(",").append((int) event.getY(i));
                        if (i + 1 < event.getPointerCount())
                                sb.append(";");
                }
                sb.append("]");
                //Log.d(TAG, sb.toString());
        }

       
        private float spacing(MotionEvent event) {
                float x = event.getX(0) - event.getX(1);
                float y = event.getY(0) - event.getY(1);
                return FloatMath.sqrt(x * x + y * y);
        }

       
        private void midPoint(PointF point, MotionEvent event) {
                float x = event.getX(0) + event.getX(1);
                float y = event.getY(0) + event.getY(1);
                point.set(x / 2, y / 2);
        }
}
将以上代码写到MulitPointTouchListener .java中，然后对你相应的图片进行OnTouchListener
比如：imageView.setOnTouchListener(new MulitPointTouchListener ());在xml中要将图片的缩放格式改成Matrix

 

注：android:scaleType="matrix"