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);
}
}

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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);