《Android进阶之光》--View体系与自定义View

No1：

View的滑动

1）layout()方法的

public class CustomView extends View{private int lastX;private int lastY;public CustomView(Context context,AttributeSet attrs,int defStyleAttr){super(context,attrs,defStyleAttr);}public CustomView(Context context,AttributeSet attrs){super(context,attrs);}public CustomView(Context context){super(context);}public boolean onTouchEvent(MotionEvent event){//获取手指摸点的横坐标和纵坐标int x = (int)event.getX();int y = (int)event.getY();switch(event.getAction()){case MotionEvent.ACTION_DOWN:lastX = x;lastY = y;break;case MotionEvent.ACTION_MOVE://计算移动的距离int offsetX = x - lastX;int offsetY = y - lastY;//调用layout方法来重新放置它的位置layout(getLeft()+offsetX,getTop()+offsetY,getRight()+offsetX,getBottom()+offsetY);break;}return true;}
}

2）offsetLeftAndRight()与offsetTopAndBottom()

对上面代码进行修改

case MotionEvent.ACTION_MOVE://计算移动的距离int offsetX = x - lastX;int offsetY = y - lastY;//对left和right进行偏移
    offsetLeftAndRight(offsetX);//对top和bottom进行偏移
    offsetTopAndBottom(offsetY);break;

3）LayoutParams(改变布局参数)

同样对上面代码进行修改

case MotionEvent.ACTION_MOVE:ViewGroup.MarginLayoutParams layoutParams = (ViewGroup.MarginLayoutParams)getLayoutParams();layoutParams.leftMargin = getLeft() + offsetX;layoutParams.topMargin = getTop() + offsetY;setLayoutParams(layoutParams);break;

4）动画

5）scrollTo与scrollBy

scrollTo(x,y)表示移动到一个具体的坐标点，而scrollBy(x,y)表示移动的增量为dx、dy。其中scrollBy最终也是要调用scrollTo的。

View.java的scrollBy和scrollTo源码

public void scrollTo(int x,int y){if(mScrollX!=x || mScrollY!=y){int oldX = mScrollX;int oldY = mScrollY;mScrollX = x;mScrollY = y;invalidateParentCaches();onScrollChanged(mScrollX,mScrollY,oldX,oldY);if(!awakenScrollBars()){postInvalidateOnAnimation();}}
}public void scrollBy(int x,int y){scrollTo(mScrollX+x,mScrollY+y);
}

6）Scroller

public CustomView(Context context,AttributeSet attrs){super(context,attrs);mScroller = new Scroller(context);
}@Override
public void computeScroll(){super.computeScroll();if(mScroller.computeScrollOffset()){((View)getParent()).scrollTo(mScroller.getCurrX(),mScroller.getCurrY());invalidate();}
}public void smoothScrollTo(int destX,int destY){int scrollX = getScrollX();int delta = destX-scrollX;mScroller.startScroll(scrollX,0,delta,0,2000);invalidate();
}//最后调用
mCustomView.smoothScrollTo(-400,0);