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
我使用的是FirebaseListAdapter,不能让任何解决方案工作。我最后做了这个。我猜有更优雅的方式,但这是一个完整的和有效的解决方案。
在onCreate之前:
private int reset;
private int top;
private int index;
FirebaseListAdapter内部:
@Override
public void onDataChanged() {
super.onDataChanged();
// Only do this on first change, when starting
// activity or coming back to it.
if(reset == 0) {
mListView.setSelectionFromTop(index, top);
reset++;
}
}
启动时间:
@Override
protected void onStart() {
super.onStart();
if(adapter != null) {
adapter.startListening();
index = 0;
top = 0;
// Get position from SharedPrefs
SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(this);
top = sharedPref.getInt("TOP_POSITION", 0);
index = sharedPref.getInt("INDEX_POSITION", 0);
// Set reset to 0 to allow change to last position
reset = 0;
}
}
停止:
@Override
protected void onStop() {
super.onStop();
if(adapter != null) {
adapter.stopListening();
// Set position
index = mListView.getFirstVisiblePosition();
View v = mListView.getChildAt(0);
top = (v == null) ? 0 : (v.getTop() - mListView.getPaddingTop());
// Save position to SharedPrefs
SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(this);
sharedPref.edit().putInt("TOP_POSITION" + "", top).apply();
sharedPref.edit().putInt("INDEX_POSITION" + "", index).apply();
}
}
因为我还必须解决这个FirebaseRecyclerAdapter,我在这里发布的解决方案:
在onCreate之前:
private int reset;
private int top;
private int index;
FirebaseRecyclerAdapter内部:
@Override
public void onDataChanged() {
// Only do this on first change, when starting
// activity or coming back to it.
if(reset == 0) {
linearLayoutManager.scrollToPositionWithOffset(index, top);
reset++;
}
}
启动时间:
@Override
protected void onStart() {
super.onStart();
if(adapter != null) {
adapter.startListening();
index = 0;
top = 0;
// Get position from SharedPrefs
SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(this);
top = sharedPref.getInt("TOP_POSITION", 0);
index = sharedPref.getInt("INDEX_POSITION", 0);
// Set reset to 0 to allow change to last position
reset = 0;
}
}
停止:
@Override
protected void onStop() {
super.onStop();
if(adapter != null) {
adapter.stopListening();
// Set position
index = linearLayoutManager.findFirstVisibleItemPosition();
View v = linearLayoutManager.getChildAt(0);
top = (v == null) ? 0 : (v.getTop() - linearLayoutManager.getPaddingTop());
// Save position to SharedPrefs
SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(this);
sharedPref.edit().putInt("TOP_POSITION" + "", top).apply();
sharedPref.edit().putInt("INDEX_POSITION" + "", index).apply();
}
}
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
为了澄清Ryan Newsom的精彩回答并针对片段进行调整通常情况下,我们想要从主ListView片段导航到细节片段然后再返回主ListView片段
private View root;
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
if(root == null){
root = inflater.inflate(R.layout.myfragmentid,container,false);
InitializeView();
}
return root;
}
public void InitializeView()
{
ListView listView = (ListView)root.findViewById(R.id.listviewid);
BaseAdapter adapter = CreateAdapter();//Create your adapter here
listView.setAdpater(adapter);
//other initialization code
}
这里的“神奇”是,当我们从细节片段导航回ListView片段时,视图不会被重新创建,我们不设置ListView的适配器,所以一切都保持不变!
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。
对于一些正在寻找此问题解决方案的人来说,问题的根源可能在于您设置列表视图适配器的位置。在列表视图上设置适配器后,它将重置滚动位置。只是需要考虑一下。我移动设置适配器到我的onCreateView后,我们抓取引用到列表视图,它解决了我的问题。=)
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)
}
推荐文章
- 在android中从上下文获取活动
- 无法解析主机"<URL here>"没有与主机名关联的地址
- getActivity()在Fragment函数中返回null
- 按钮背景是透明的
- 在Mac OS X上哪里安装Android SDK ?
- 我如何获得图像缩放功能?
- 在Android应用程序中显示当前时间和日期
- BottomSheetDialogFragment的圆角
- 在应用程序启动时出现“无法获得BatchedBridge,请确保您的bundle被正确打包”的错误
- 我如何改变默认对话框按钮的文本颜色在安卓5
- 更改单选按钮的圆圈颜色
- 如何在android中复制一个文件?
- adb找不到我的设备/手机(MacOS X)
- 如何在新的材质主题中改变背面箭头的颜色?
- androidviewpager与底部点