Drag Events 最酷的地方在于，您也可以在 parent 中监听ViewGroup 它们。扩展GridView并覆盖onDragEvent到监视器DragEvent.ACTION_DRAG_LOCATION。在那里，获取拖动的 Y 坐标 ( event.getY())。确保从 中返回 true ACTION_DRAG_STARTED，否则您将不会在 中收到事件ACTION_DRAG_LOCATION。
确定您的“命中框”，可能使用jaibatrik 建议的技术，或者仅使用 GridView 测量高度的百分比。
使用 可能最有意义smoothScrollByOffset(int offset)，这样您就可以实现步进/指数滚动。这意味着，用户将拖动的项目保留在点击框中的时间越长，偏移量就越大。
对于开源库/组件来说，这听起来像是一个很酷的想法。;-)
编辑：
这是一个如何执行此操作的示例：
import android.app.Activity;
import android.content.ClipData;
import android.content.ClipData.Item;
import android.content.Context;
import android.os.Bundle;
import android.util.Log;
import android.view.DragEvent;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemLongClickListener;
import android.widget.ArrayAdapter;
import android.widget.GridView;
public class GridDragActivity extends Activity implements OnItemLongClickListener {
private static final String TAG = "GridDragActivity";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
MyGridView gridView = new MyGridView(this);
gridView.setNumColumns(3);
gridView.setOnItemLongClickListener(this);
gridView.setAdapter(new ArrayAdapter<String>(
this,
android.R.layout.simple_list_item_1,
COUNTRIES));
setContentView(gridView);
}
@Override
public boolean onItemLongClick(AdapterView<?> parent, View view, int position,
long id) {
ClipData data = ClipData.newPlainText((String) view.getTag(),
String.valueOf(position));
View.DragShadowBuilder shadow = new View.DragShadowBuilder(view);
view.startDrag(data, shadow, null, 0);
return true;
}
class MyGridView extends GridView {
private static final int THRESHHOLD = 200;
private static final int OFFSET = 10;
public MyGridView(Context context) {
super(context);
}
@Override
public boolean onDragEvent(DragEvent event) {
int height = getMeasuredHeight();
switch (event.getAction()) {
case DragEvent.ACTION_DRAG_STARTED:
return true;
case DragEvent.ACTION_DRAG_LOCATION:
float y = event.getY();
if (height - y < THRESHHOLD) {
smoothScrollByOffset(OFFSET);
} else if (height - y > height - THRESHHOLD) {
smoothScrollByOffset(-OFFSET);
}
return true;
case DragEvent.ACTION_DROP:
ClipData data = event.getClipData();
Item item = data.getItemAt(0);
int start = Integer.valueOf((String) item.getText());
int end = pointToPosition((int) event.getX(), (int) event.getY());
Log.i(TAG, "DROP started at = " + start + ", ended at = " + end);
return true;
}
return super.onDragEvent(event);
}
}
static final String[] COUNTRIES = new String[] {
"Afghanistan", "Albania", "Algeria", "American Samoa", "Andorra",
"Angola", "Anguilla", "Antarctica", "Antigua and Barbuda", "Argentina",
"Armenia", "Aruba", "Australia", "Austria", "Azerbaijan",
"Bahrain", "Bangladesh", "Barbados", "Belarus", "Belgium",
"Belize", "Benin", "Bermuda", "Bhutan", "Bolivia",
"Bosnia and Herzegovina", "Botswana", "Bouvet Island", "Brazil",
"British Indian Ocean Territory",
"British Virgin Islands", "Brunei", "Bulgaria", "Burkina Faso", "Burundi",
"Cote d'Ivoire", "Cambodia", "Cameroon", "Canada", "Cape Verde",
"Cayman Islands", "Central African Republic", "Chad", "Chile", "China",
"Christmas Island", "Cocos (Keeling) Islands", "Colombia", "Comoros", "Congo",
"Cook Islands", "Costa Rica", "Croatia", "Cuba", "Cyprus", "Czech Republic",
"Democratic Republic of the Congo", "Denmark", "Djibouti", "Dominica",
"Dominican Republic",
"East Timor", "Ecuador", "Egypt", "El Salvador", "Equatorial Guinea", "Eritrea",
"Estonia", "Ethiopia", "Faeroe Islands", "Falkland Islands", "Fiji", "Finland",
"Former Yugoslav Republic of Macedonia", "France", "French Guiana", "French Polynesia",
"French Southern Territories", "Gabon", "Georgia", "Germany", "Ghana", "Gibraltar",
"Greece", "Greenland", "Grenada", "Guadeloupe", "Guam", "Guatemala", "Guinea",
"Guinea-Bissau",
"Guyana", "Haiti", "Heard Island and McDonald Islands", "Honduras", "Hong Kong",
"Hungary"
};
}