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

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.

其他回答

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);
    }
}

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。

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)
}

使用下面的代码:

int index,top;

@Override
protected void onPause() {
    super.onPause();
    index = mList.getFirstVisiblePosition();

    View v = challengeList.getChildAt(0);
    top = (v == null) ? 0 : (v.getTop() - mList.getPaddingTop());
}

无论何时你刷新你的数据使用下面的代码:

adapter.notifyDataSetChanged();
mList.setSelectionFromTop(index, top);

警告! !在AbsListView中有一个错误,如果ListView.getFirstVisiblePosition()为0,则不允许onSaveState()正确工作。

所以,如果你有大图像,占据了屏幕的大部分,你滚动到第二张图像,但第一张图像的一部分正在显示,滚动位置将不会被保存…

从AbsListView.java:1650(评论我)

// this will be false when the firstPosition IS 0
if (haveChildren && mFirstPosition > 0) {
    ...
} else {
    ss.viewTop = 0;
    ss.firstId = INVALID_POSITION;
    ss.position = 0;
}

但在这种情况下,下面代码中的“top”将是一个负数,这将导致其他问题,阻止状态被正确恢复。所以当'top'为负时,就得到下一个子结点

// save index and top position
int index = getFirstVisiblePosition();
View v = getChildAt(0);
int top = (v == null) ? 0 : v.getTop();

if (top < 0 && getChildAt(1) != null) {
    index++;
    v = getChildAt(1);
    top = v.getTop();
}
// parcel the index and top

// when restoring, unparcel index and top
listView.setSelectionFromTop(index, top);