类似iPhone的弹性ListView滚动

从2.3开始，android开始支持listview的overscroll, 应该很方便可以做出类似iPhone的弹性滚动，及越过list顶端或者底端，然后弹性滚回。昨天google了半天的例子，一个没找到，今天又试了试，发现用很简单的方式就可以实现这个效果。大致如下：
继承ListView

private int delY; 

  private boolean action_up; 

在 onTouchEvent(){ 

           ... 

          case MotionEvent.ACTION_MOVE: 

            delY = (int) (preY - y); 

            preY = y; 

            break; 

          case MotionEvent.ACTION_UP: 

             action_up = true; 

            break; 

}

然后在2.3新增的onOverScrolled方法中做如下实现

protected void onOverScrolled(int scrollX, int scrollY, boolean clampedX,
   boolean clampedY) {
    this.scrollBy(0, delY / 2);
    if (action_up) {
      this.scrollTo(0, 0);
  }
}

--------------------------------------------------------------------------------------

类似iPhone弹性效果的BounceListView

public class BounceListView extends ListView{
    private static final int MAX_Y_OVERSCROLL_DISTANCE = 200;
     
    private Context mContext;
    private int mMaxYOverscrollDistance;
     
    public BounceListView(Context context){
        super(context);
        mContext = context;
        initBounceListView();
    }
     
    public BounceListView(Context context, AttributeSet attrs){
        super(context, attrs);
        mContext = context;
        initBounceListView();
    }
     
    public BounceListView(Context context, AttributeSet attrs, int defStyle){
        super(context, attrs, defStyle);
        mContext = context;
        initBounceListView();
    }
     
    private void initBounceListView(){
        //get the density of the screen and do some maths with it on the max overscroll distance
        //variable so that you get similar behaviors no matter what the screen size
         
        final DisplayMetrics metrics = mContext.getResources().getDisplayMetrics();
        final float density = metrics.density;
         
        mMaxYOverscrollDistance = (int) (density * MAX_Y_OVERSCROLL_DISTANCE);
    }
     
    @Override
    protected boolean overScrollBy(int deltaX, int deltaY, int scrollX, int scrollY, int scrollRangeX, int scrollRangeY, int maxOverScrollX, int maxOverScrollY, boolean isTouchEvent){ 
        //This is where the magic happens, we have replaced the incoming maxOverScrollY with our own custom variable mMaxYOverscrollDistance; 
        return super.overScrollBy(deltaX, deltaY, scrollX, scrollY, scrollRangeX, scrollRangeY, maxOverScrollX, mMaxYOverscrollDistance, isTouchEvent);  
    }
     
}

附送：

用字符串显示图片

做项目过程中遇到一个问题，从数据库里读取图片名称，然后调用图片。直接用R.drawable.?无法调用。查了好多地方最后找到了个方法，分享给大家，希望有帮助。

主要由两种方法，个人建议第二种。

1. 不把图片放在res/drawable下，而是存放在src某个package中（如：com.drawable.resource），这种情况下的调用方法为：

String path = "com/drawable/resource/image.png";

InputStream is = getClassLoader().getResourceAsStream(path);

Drawable.createFromStream(is, "src");

2. 如果还是希望直接使用res/drawable中的图片，就需要通过下面的方法了：

假设创建工程的时候，填写的package名字为：com.test.image

int resID = getResources().getIdentifier("goto_radar", "drawable", "com.test.image");

Drawable image = getResources().getDrawable(resID);