Android实现图片随意拖动、缩放

1.重写一个实现View.OnTouchListener的类，这里使用的是Matrix实现

import android.graphics.Matrix;
import android.graphics.PointF;
import android.view.MotionEvent;
import android.view.View;
import android.widget.ImageView;

public class MulitPointTouchListener implements View.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());

                mode = DRAG;



                break;
            case MotionEvent.ACTION_POINTER_DOWN:
                oldDist = spacing(event);

                if (oldDist > 10f) {
                    savedMatrix.set(matrix);
                    midPoint(mid, event);
                    mode = ZOOM;

                }
                break;
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_POINTER_UP:
                mode = NONE;


                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);

                    if (newDist > 10f) {
                        matrix.set(savedMatrix);
                        float scale = newDist / oldDist;
                        matrix.postScale(scale, scale, mid.x, mid.y);
                    }
                }
                break;
        }

        view.setImageMatrix(matrix);
        return true;
    }

    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("]");

    }


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

2.使用

imgTest.setOnTouchListener(new MulitPointTouchListener());

3.缺陷:图片的缩放和拖动都是在原图片大小的那块区域展现，放大的话，放大的部分都被遮住了，如果是移动的话，可能把图片给移动没了。