MainActivity如下:
package cc.testscroller2;
import android.os.Bundle;
import android.app.Activity;
/**
* Demo描述:
* 实现可以拉动后回弹的布局.
* 类似于下拉刷新的.
*
* 参考资料:
* 1 http://gundumw100.iteye.com/blog/1884373
* 2 http://blog.****.net/gemmem/article/details/7321910
* 3 http://ipjmc.iteye.com/blog/1615828
* 4 http://blog.****.net/c_weibin/article/details/7438323
* 5 http://www.cnblogs.com/wanqieddy/archive/2012/05/05/2484534.html
* 6 http://blog.****.net/hudashi/article/details/7353075
* Thank you very much
*/
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
}
package cc.testscroller2;
import android.content.Context;
import android.util.AttributeSet;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.widget.LinearLayout;
import android.widget.Scroller;
/**
* 总体思路:
* 处理View的Touch事件,即重写onTouchEvent()方法:
* 当手指抬起时将其回到原点,其余情况交给GestureDetector处理.
*
* 在GestureDetector中重点是覆写onScroll()方法.在该方法中得到
* Y方向滑动的距离,从而设置 mScroller.startScroll()方法,准备滑动.
* 随之刷新界面invalidate()从而执行方法computeScroll().
* 在computeScroll()方法中调用 scrollTo()方法实现真正的滑动.
*
* 注意事项:
* 1 scrollTo()方法的参数:
* scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
* 并且在此之后也要调用postInvalidate()进行刷新
*
*
* 方法说明:
* 1 mScroller.getFinalX(Y)()
* The final X(Y) offset as an absolute distance from the origin.
* 返回滚动结束位置(得到当前X(Y)距离原始位置的值).仅针对"fling"滚动有效.
* 也就是说该方法是针对滚动结束而言的.
*
* 坐标方向:
* X方向的距离,正数向左,负数向右
* Y方向的距离,正数向上,负数向下
*
* 2 mScroller.getCurrX(Y)()
* The new X offset as an absolute distance from the origin.
* The new Y offset as an absolute distance from the origin.
* 返回当前滚动 X(Y)方向的偏移
* 也就是说该方法是针对滚动中而言的.
*
* 坐标方向:
* X方向的距离,正数向左,负数向右
* Y方向的距离,正数向上,负数向下
*
* 3 invalidate()与postInvalidate()的区别
* invalidate()在UI线程自身中使用;postInvalidate()在非UI线程中使用.
* 这是目前网络资料的普遍说法,还待进一步研究.
*
* 4 startScroll(int startX, int startY, int dx, int dy, int duration)
* 第一,二个参数起始位置;第三,四个滚动的偏移量;第五个参数持续时间
*
*
*/
public class BounceableLinearLayout extends LinearLayout {
private Scroller mScroller;
private GestureDetector mGestureDetector;
public BounceableLinearLayout(Context context) {
this(context, null);
}
public BounceableLinearLayout(Context context, AttributeSet attrs) {
super(context, attrs);
setClickable(true);
setLongClickable(true);
mScroller = new Scroller(context);
mGestureDetector = new GestureDetector(context, new GestureListenerImpl());
}
@Override
public void computeScroll() {
if (mScroller.computeScrollOffset()) {
System.out.println("computeScroll()---> "+
"mScroller.getCurrX()="+mScroller.getCurrX()+","+
"mScroller.getCurrY()="+mScroller.getCurrY());
scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
//必须执行postInvalidate()从而调用computeScroll()
//其实,在此调用invalidate();亦可
postInvalidate();
}
super.computeScroll();
}
@Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_UP :
//手指抬起时回到最初位置
prepareScroll(0, 0);
break;
default:
//其余情况交给GestureDetector手势处理
return mGestureDetector.onTouchEvent(event);
}
return super.onTouchEvent(event);
}
class GestureListenerImpl implements GestureDetector.OnGestureListener {
@Override
public boolean onDown(MotionEvent e) {
return true;
}
@Override
public void onShowPress(MotionEvent e) {
}
@Override
public boolean onSingleTapUp(MotionEvent e) {
return false;
}
//控制拉动幅度:
//int disY=(int)((distanceY - 0.5)/2);
//亦可直接调用:
//smoothScrollBy(0, (int)distanceY);
@Override
public boolean onScroll(MotionEvent e1, MotionEvent e2,float distanceX, float distanceY) {
int disY = (int) ((distanceY - 0.5) / 2);
beginScroll(0, disY);
return false;
}
public void onLongPress(MotionEvent e) {
}
@Override
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,float velocityY) {
return false;
}
}
//滚动到目标位置
protected void prepareScroll(int fx, int fy) {
int dx = fx - mScroller.getFinalX();
int dy = fy - mScroller.getFinalY();
beginScroll(dx, dy);
}
//设置滚动的相对偏移
protected void beginScroll(int dx, int dy) {
System.out.println("smoothScrollBy()---> dx="+dx+",dy="+dy);
//第一,二个参数起始位置;第三,四个滚动的偏移量
mScroller.startScroll(mScroller.getFinalX(), mScroller.getFinalY(), dx, dy);
System.out.println("smoothScrollBy()---> " +
"mScroller.getFinalX()="+mScroller.getFinalX()+","+
"mScroller.getFinalY()="+mScroller.getFinalY());
//必须执行invalidate()从而调用computeScroll()
invalidate();
}
}
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<cc.testscroller2.BounceableLinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="向下拉动后松开"
/>
</cc.testscroller2.BounceableLinearLayout>
</RelativeLayout>