我有一个很长的ListView,用户可以在返回前一个屏幕之前滚动它。当用户再次打开这个ListView时,我希望列表被滚动到与之前相同的位置。关于如何实现这一点,你有什么想法吗?
当前回答
如果在重新加载前保存状态,并在重新加载后恢复状态,则可以在重新加载后保持滚动状态。在我的情况下,我做了一个异步网络请求,并在它完成后在回调中重新加载列表。这是我恢复状态的地方。代码示例是Kotlin。
val state = myList.layoutManager.onSaveInstanceState()
getNewThings() { newThings: List<Thing> ->
myList.adapter.things = newThings
myList.layoutManager.onRestoreInstanceState(state)
}
其他回答
If you are saving/restoring scroll position of ListView yourself you are essentially duplicating the functionality already implemented in android framework. The ListView restores fine scroll position just well on its own except one caveat: as @aaronvargas mentioned there is a bug in AbsListView that won't let to restore fine scroll position for the first list item. Nevertheless the best way to restore scroll position is not to restore it. Android framework will do it better for you. Just make sure you have met the following conditions:
确保你没有调用setSaveEnabled(false)方法,也没有为xml布局文件中的列表设置android:saveEnabled="false"属性 为ExpandableListView重写long getCombinedChildId(long groupId, long childId)方法,使其返回正长数(BaseExpandableListAdapter类中的默认实现返回负数)。下面是一些例子:
.
@Override
public long getChildId(int groupPosition, int childPosition) {
return 0L | groupPosition << 12 | childPosition;
}
@Override
public long getCombinedChildId(long groupId, long childId) {
return groupId << 32 | childId << 1 | 1;
}
@Override
public long getGroupId(int groupPosition) {
return groupPosition;
}
@Override
public long getCombinedGroupId(long groupId) {
return (groupId & 0x7FFFFFFF) << 32;
}
如果在一个片段中使用了ListView或ExpandableListView,不要在活动重新创建片段(例如在屏幕旋转后)。使用findFragmentByTag(String标签)方法获取片段。 确保ListView有一个唯一的android:id。
To avoid aforementioned caveat with first list item you can craft your adapter the way it returns special dummy zero pixels height view for the ListView at position 0. Here is the simple example project shows ListView and ExpandableListView restore their fine scroll positions whereas their scroll positions are not explicitly saved/restored. Fine scroll position is restored perfectly even for the complex scenarios with temporary switching to some other application, double screen rotation and switching back to the test application. Please note, if you are explicitly exiting the application (by pressing the Back button) the scroll position won't be saved (as well as all other Views won't save their state). https://github.com/voromto/RestoreScrollPosition/releases
Parcelable state;
@Override
public void onPause() {
// Save ListView state @ onPause
Log.d(TAG, "saving listview state");
state = listView.onSaveInstanceState();
super.onPause();
}
...
@Override
public void onViewCreated(final View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
// Set new items
listView.setAdapter(adapter);
...
// Restore previous state (including selected item index and scroll position)
if(state != null) {
Log.d(TAG, "trying to restore listview state");
listView.onRestoreInstanceState(state);
}
}
试试这个:
// save index and top position
int index = mList.getFirstVisiblePosition();
View v = mList.getChildAt(0);
int top = (v == null) ? 0 : (v.getTop() - mList.getPaddingTop());
// ...
// restore index and position
mList.setSelectionFromTop(index, top);
Explanation: ListView.getFirstVisiblePosition() returns the top visible list item. But this item may be partially scrolled out of view, and if you want to restore the exact scroll position of the list you need to get this offset. So ListView.getChildAt(0) returns the View for the top list item, and then View.getTop() - mList.getPaddingTop() returns its relative offset from the top of the ListView. Then, to restore the ListView's scroll position, we call ListView.setSelectionFromTop() with the index of the item we want and an offset to position its top edge from the top of the ListView.
我采用了@(Kirk Woll)建议的解决方案,它对我很有效。我还在“联系人”应用程序的Android源代码中看到,他们使用了类似的技术。我还想补充一些具体情况: 在我的listactivity派生类的顶部:
private static final String LIST_STATE = "listState";
private Parcelable mListState = null;
然后,一些方法重写:
@Override
protected void onRestoreInstanceState(Bundle state) {
super.onRestoreInstanceState(state);
mListState = state.getParcelable(LIST_STATE);
}
@Override
protected void onResume() {
super.onResume();
loadData();
if (mListState != null)
getListView().onRestoreInstanceState(mListState);
mListState = null;
}
@Override
protected void onSaveInstanceState(Bundle state) {
super.onSaveInstanceState(state);
mListState = getListView().onSaveInstanceState();
state.putParcelable(LIST_STATE, mListState);
}
当然,“loadData”是我从DB中检索数据并将其放入列表的函数。
在我的Froyo设备上,当你改变手机方向时,当你编辑一个项目并返回列表时,这都是有效的。
private Parcelable state;
@Override
public void onPause() {
state = mAlbumListView.onSaveInstanceState();
super.onPause();
}
@Override
public void onResume() {
super.onResume();
if (getAdapter() != null) {
mAlbumListView.setAdapter(getAdapter());
if (state != null){
mAlbumListView.requestFocus();
mAlbumListView.onRestoreInstanceState(state);
}
}
}
这就够了
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