Android触摸放大缩小

Android的触摸放大缩小功能可以通过实现GestureDetector类来实现。以下是一个简单的示例代码：

public class MyView extends View {
    private Paint paint;
    private Bitmap bitmap;
    private float scaleFactor = 1.0f;
    private GestureDetector gestureDetector;

    public MyView(Context context) {
        super(context);
        init();
    }

    public MyView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        paint = new Paint();
        bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.image);
        gestureDetector = new GestureDetector(getContext(), new MyGestureListener());
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        gestureDetector.onTouchEvent(event);
        return true;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        canvas.save();
        canvas.scale(scaleFactor, scaleFactor);
        canvas.drawBitmap(bitmap, 0, 0, paint);
        canvas.restore();
    }

    private class MyGestureListener extends GestureDetector.SimpleOnGestureListener {
        @Override
        public boolean onScale(ScaleGestureDetector detector) {
            scaleFactor *= detector.getScaleFactor();
            scaleFactor = Math.max(0.1f, Math.min(scaleFactor, 5.0f));
            invalidate();
            return true;
        }
    }
}

在这个示例中，我们使用了GestureDetector和ScaleGestureDetector来实现放大缩小功能。我们在MyView类中重写了onTouchEvent()方法来接收触摸事件，然后将事件传递给gestureDetector处理。在MyGestureListener类中，我们重写了onScale()方法，该方法在用户进行放大缩小手势时被调用，我们在此方法中更新scaleFactor变量，然后调用invalidate()方法强制视图重新绘制。最后，在onDraw()方法中，我们调用canvas.scale()方法来缩放画布，然后绘制位图。