我正试着在安卓(冰淇淋三明治)的ListView
中实现拖放。因此,当被拖动的对象到达ListView
的边缘时,我将在相关方向上滚动ListView
。问题是,当我们滚动时,有时适配器会根据需要创建新的View
,并且这些“新的”View
没有早先接收到ACTION_DRAG_STARTED
事件,因此没有接收到DragEvent
更新。有没有办法我也可以把事件发送到这些视图?
发布于 2012-12-14 16:57:09
在listview中实现拖放的最简单方法是使用这个很棒的库。https://github.com/commonsguy/cwac-touchlist,值得一试。
发布于 2012-12-11 16:43:24
查看View的源代码,我看到:
static final int DRAG_CAN_ACCEPT = 0x00000001;
int mPrivateFlags2;
boolean canAcceptDrag() {
return (mPrivateFlags2 & DRAG_CAN_ACCEPT) != 0;
}
mPrivateFlags2是包私有的,不会被SDK公开。但是,您应该能够通过执行以下操作在子类中更改它:
try {
Field mPrivateFlags2 = this.getClass().getField("mPrivateFlags2");
int currentValue = mPrivateFlags2.getInt(this);
mPrivateFlags2.setInt(this, currentValue | 0x00000001);
} catch (Exception e) {
}
发布于 2013-01-03 02:09:58
我有same problem。我没有解决这个回收问题,但我发现了一个可能的变通方法,仍然使用拖放框架。这个想法是为了改变视角:不是在列表中的每个View
上使用OnDragListener
,而是可以直接在ListView
上使用它。
然后,在执行拖放操作时,找到手指位于哪个项目的顶部,并在ListView
的ListAdapter
中编写相关的显示代码。然后,技巧是找到我们在哪个项目视图的顶部,以及在哪里完成了拖放。
为此,我将适配器创建的每个视图的ListView
位置设置为id
-使用View.setId()
,这样我以后就可以使用ListView.pointToPosition()
和ListView.findViewById()
的组合找到它。
作为一个拖拽监听器的例子(我提醒你,这是在ListView
上应用的),它可以是这样的:
// Initalize your ListView
private ListView _myListView = new ListView(getContext());
// Start drag when long click on a ListView item
_myListView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
@Override
public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {
DragShadowBuilder shadowBuilder = new View.DragShadowBuilder(view);
view.startDrag(null, shadowBuilder, _myListView.getItemAtPosition(position), 0);
return true;
}
});
// Set the adapter and drag listener
_myListView.setOnDragListener(new MyListViewDragListener());
_myListView.setAdapter(new MyViewAdapter(getActivity()));
// Classes used above
private class MyViewAdapter extends ArrayAdapter<Object> {
public MyViewAdapter (Context context, List<TimedElement> objects) {
super(context, 0, objects);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View myView = convertView;
if (myView == null) {
// Instanciate your view
}
// Associates view and position in ListAdapter, needed for drag and drop
myView.setId(position);
return myView;
}
}
private class MyListViewDragListener implements View.OnDragListener {
@Override
public boolean onDrag(View v, DragEvent event) {
final int action = event.getAction();
switch(action) {
case DragEvent.ACTION_DRAG_STARTED:
return true;
case DragEvent.ACTION_DRAG_DROP:
// We drag the item on top of the one which is at itemPosition
int itemPosition = _myListView.pointToPosition((int)event.getX(), (int)event.getY());
// We can even get the view at itemPosition thanks to get/setid
View itemView = _myListView.findViewById(itemPosition );
/* If you try the same thing in ACTION_DRAG_LOCATION, itemView
* is sometimes null; if you need this view, just return if null.
* As the same event is then fired later, only process the event
* when itemView is not null.
* It can be more problematic in ACTION_DRAG_DROP but for now
* I never had itemView null in this event. */
// Handle the drop as you like
return true;
}
}
}
现在,如果您需要在进行拖放操作时获得视觉反馈,有几种策略可供选择。例如,在您的活动中可以有两个实例变量,名为:
private boolean ongoingDrag = false; // To know if we are in a drag&drop state
private int dragPosition = 0; // You put the itemPosition variable here
在MyListViewDragListener
中进行拖放操作时,您可以修改这些变量,并在MyViewAdapter
中使用它们的状态。当然,不要忘记使用诸如_myListView.getAdapter()).notifyDataSetChanged()
或_myListView.invalidate()
方法之类的东西来更新UI (当然,在事件线程中使用处理程序)。
https://stackoverflow.com/questions/13738371
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