图片放大缩小

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public class DragTest extends Activity {

    private ImageView dog;
    private float xl;
    private float yl;
    private final int MODE_DRAG = 1;
    private final int MODE_ZOOM = 2;
    private final int MODE_NONE = 0;
    private int currentMode = MODE_NONE;
    private double distanceStart;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_drag_test);
        initView();
    }

    Matrix matrix = new Matrix();
    Matrix matrixNew = new Matrix();
    private void initView() {
        dog = (ImageView) findViewById(R.id.dog);
        dog.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                switch (event.getAction() & MotionEvent.ACTION_MASK) {
                    case MotionEvent.ACTION_DOWN:
                        currentMode = MODE_DRAG;
                        xl = event.getX();
                        yl = event.getY();
                        matrix.set(dog.getImageMatrix());
                        break;
                    case MotionEvent.ACTION_POINTER_DOWN:
                           distanceStart = spacing(event);
                        if (distanceStart > 20) {
                            currentMode = MODE_ZOOM;
                            matrix.set(dog.getImageMatrix());
                        }
                        break;
                    case MotionEvent.ACTION_MOVE:
                        if (currentMode == MODE_DRAG) {
                            matrixNew.set(matrix);
                            float xn = event.getX();
                            float yn = event.getY();
                            //matrix.setTranslate(xn,yn);
                            matrixNew.postTranslate(xn - xl,yn -yl);
                        } else if (currentMode == MODE_ZOOM) {
                            double distance = spacing(event);
                            float scale = (float) (distance / distanceStart);
                            matrixNew.postScale(scale,scale);
                        }

                        break;
                    case MotionEvent.ACTION_UP:
                        currentMode = MODE_NONE;
                        break;
                }
                dog.setImageMatrix(matrixNew);
                return true;
            }
        });
    }

       private double spacing(MotionEvent event) {
        float x = 0;
        float y = 0;
        try {
            x = event.getX(0) - event.getX(1);
            y = event.getY(0) - event.getY(1);
        } catch (IllegalArgumentException e) {}
        return Math.sqrt(x * x + y * y);
    }
}