View基础

1.View坐标系

我随便设置了一个View，打印如下两句日志，可验证出结果：
(1)Bottom确实比Top的值大，即Y坐标轴的正方向是向下的
(2)height = bottom - top; width = right - left

Log.d("thmtest","top = "+view.getTop()+" & left = "+view.getLeft() +" &bottom = "+view.getBottom()+ "& right = "+view.getRight());Log.d("thmtest", "width = "+view.getWidth() +" &height = "+view.getHeight());

08-09 13:58:55.125 18893-18893/com.thm.testview D/thmtest: top = 250 & left = 0 &bottom = 467& right = 87308-09 13:58:55.125 18893-18893/com.thm.testview D/thmtest: width = 873 &height = 217

2、MotionEvent、TouchSlop

MotionEvent

getX()/getY()和getRawX()/getRawY()的区别
前者是相对于控件的原点，即左上角，(left, top)
后者是相对于坐标系的原点，即屏幕的左上角，(0,0)

TouchSlop

最小滑动距离，手指滑动低于这个值，认为不是滑动操作
获取方式：

int touchSlop = ViewConfiguration.get(getContext())                .getScaledTouchSlop();

3、VelocityTracker

可用于获取滑动速度，用于做一些手势速度的相关逻辑处理
使用方法：

VelocityTracker mVelocityTracker = VelocityTracker.obtain();

public boolean onTouchEvent(MotionEvent event) {        mVelocityTracker.addMovement(event);        switch (event.getAction()) {            case MotionEvent.ACTION_DOWN:                break;            case MotionEvent.ACTION_MOVE:                break;            case MotionEvent.ACTION_UP: {                mVelocityTracker.computeCurrentVelocity(1000);                float xVelocity = mVelocityTracker.getXVelocity();                if (Math.abs(xVelocity) > targetValue) {                    //do something                }                 break;            }            default:                break;        }        return true;    }

4、GestureDetector

手势动作处理基本上都在onTouchEvent中，
但是GestureDetector也可用于监听用户的手势动作，做出处理
使用方法：

private GestureDetector mGestureDetector  = new GestureDetector(getContext(),new GestureListener());    @Override    public boolean onTouchEvent(MotionEvent event) {        return mGestureDetector.onTouchEvent(event);    }    class GestureListener extends GestureDetector.SimpleOnGestureListener{        public boolean onSingleTapUp(MotionEvent e) {            return false;        }        public void onLongPress(MotionEvent e) {        }        public boolean onScroll(MotionEvent e1, MotionEvent e2,                                float distanceX, float distanceY) {            return false;        }        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,                               float velocityY) {            return false;        }        public void onShowPress(MotionEvent e) {        }        public boolean onDown(MotionEvent e) {            return false;        }        public boolean onDoubleTap(MotionEvent e) {            return false;        }        public boolean onDoubleTapEvent(MotionEvent e) {            return false;        }        public boolean onSingleTapConfirmed(MotionEvent e) {            return false;        }    }