android 多点触控

在android中多指触控通过OnTouchListener监听器监听，触控事件在onTouch方法中分析处理。

在单指触控中，我们常用的三个方法ACTION_DOWN、ACTION_UP、ACTION_MOVE，在多指触控中也会用到，不过用法稍有不同。

多指触控中多了ACTION_POINTER_DOWN、ACTION_POINTER_UP两种情况，这几个情况的触发用法在下面源码中标注：

        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_DOWN:  //第一根手指按下时触发
                mode = 1;
                break;
            case MotionEvent.ACTION_POINTER_DOWN: //第二根或以上的手指按下时触发
                mode += 1;
                break;
            case MotionEvent.ACTION_UP:  //所有手指都离开时触发
                mode = 0;
                break;
            case MotionEvent.ACTION_POINTER_UP:  //当有两根及以上手指触碰屏幕，其一离开时触发
                mode -= 1;
                break;
            case MotionEvent.ACTION_MOVE: //此事件非常灵敏，只要有手指触碰屏幕，便会一直触发
                if (mode >= 2) {
                    
                }
                break;
        }

 触碰的手指数可用event.getPointerCount()方法获取。

 

放大缩小：

此功能可通过手指之间的前后距离倍数来确定放大缩小的倍数，不这样稍微麻烦了点，我们可以用ScaleGestureDetector来实现：

scaleGestureDetector = new ScaleGestureDetector(this, new ScaleGestureDetector.OnScaleGestureListener() {
            @Override
            public boolean onScale(ScaleGestureDetector detector) {
                float factor = detector.getScaleFactor();
                float x = detector.getFocusX();
                float y = detector.getFocusY();
                Show.log("onScale:" + factor + ";" + x + ";" + y);
                matrix.postScale(factor, factor, x, y);
                iv.setImageMatrix(matrix);
                return true;
            }

            @Override
            public boolean onScaleBegin(ScaleGestureDetector detector) {
                Show.log("onScaleBegin");
                return true;
            }

            @Override
            public void onScaleEnd(ScaleGestureDetector detector) {
                Show.log("onScaleEnd");
            }
        });
        iv = (ImageView) findViewById(R.id.img_test);
        iv.setOnTouchListener(new OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {\
                scaleGestureDetector.onTouchEvent(event);
                return true;
            }
        });

 

多指滑动：

 先获取各点的中点，而后根据中点的位移来进行判断，下面是一个简单样例：

public class MainActivity extends Activity {

    private ImageView iv;
    Matrix matrix = new Matrix();

    private PointF startPoint;
    private PointF nowPoint;

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

        startPoint = new PointF();
        nowPoint = new PointF();

        iv = (ImageView) findViewById(R.id.img_test);
        iv.setOnTouchListener(new OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                switch (event.getAction() & MotionEvent.ACTION_MASK) {
                    case MotionEvent.ACTION_DOWN:
                    case MotionEvent.ACTION_POINTER_DOWN:
                        setEventPoint(event,startPoint);
                        break;
                    case MotionEvent.ACTION_MOVE:
                       setEventPoint(event,nowPoint);
                        Show.log("move:"+getDistance(startPoint,nowPoint));
                        matrix.postTranslate(nowPoint.x-startPoint.x,nowPoint.y-startPoint.y);
                        startPoint.set(nowPoint.x,nowPoint.y);
                        break;
                    case MotionEvent.ACTION_UP:
                        setEventPoint(event,nowPoint);
                        Show.log("end:"+getDistance(startPoint,nowPoint));
                        break;
                }
                iv.setImageMatrix(matrix);
                return true;
            }
        });
    }

    private void setEventPoint(MotionEvent event, PointF startPoint) {
        float x = 0, y = 0;
        final int pointerCount = event.getPointerCount();
        for (int i = 0; i < pointerCount; i++) {
            x += event.getX(i);
            y += event.getY(i);
        }
        x = x / pointerCount;
        y = y / pointerCount;
        startPoint.set(x,y);
    }

    private float getDistance(PointF point1,PointF point2){
        float x = point1.x-point2.x;
        float y = point1.y-point2.y;
        return (float) Math.sqrt(x * x + y * y);
    }
}