我正在更彻底地希望这个问题实际上会更容易理解。
Activity 目的 :允许用户从图库中选择图像；在 ListFragment 中显示图像的缩略图以及用户提供的图像；当用户完成保存每个图像的 uri 和标题，以及用户给这个图像集合的名称。
问题 :当设备旋转时，FragmentList 会丢失用户已经选择的所有图像和标题，即列表的所有行都丢失了。
尝试解决问题 :
adapter.notifyDataSetChanged()在 onCreate.这没有用。 adapter.notifyDataSetChanged()至onStart认为我可能需要在 Activity 生命周期的后期通知适配器。没用。 注意:我在同一个应用程序中有另一个 Activity ，它使用相同的自定义 ListViewFragment，并且 ListFragment 的状态随着设备方向的变化而保留。该 Activity 有两个主要区别: fragment 被硬编码到 .xml 中(我认为这不会产生影响，除了可能 Android 的 .xml fragment 的 native 保存与以编程方式添加的 fragment 不同)；并且该 Activity 使用 Loader 和 LoaderManager 并从我构建的 Provider 获取其数据(它从我的 SQLite 数据库收集数据)。看看这两个 Activity 之间的差异是什么让我想到“你没有以某种方式适本地处理数据馈送适配器”并启发我在设备旋转时使用 RetainedFragment 来保存 List 集合。
...这促使我考虑弄清楚如何去做，正如 Android 在他们的 Loader 页面上关于 LoaderManager 所说的那样:
"An abstract class associated with an Activity or Fragment for managing one or more Loader instances. This helps an application manage longer-running operations in conjunction with the Activity or Fragment lifecycle; the most common use of this is with a CursorLoader, however applications are free to write their own loaders for loading other types of data."
正是“加载其他类型的数据”部分让我思考“我可以使用 LoaderManager 来加载列表数据吗？我对此感到害羞的两个原因:1)我已经拥有的，至少在概念上应该可以工作；2 ) 我现在所做的根本不是“长期运行的操作”，我不认为。
研究 :
savedInstanceState !=null，我使用以下内容并且这些 fragment 的状态无需在 onSaveInstanceState() 中做任何工作即可保存(这就是为什么感觉我的问题不在于在 onSaveInstanceState 中做某事的部分原因，因为 Android 处理保存我的其他 fragment 状态，所以它不应该也使用 ListFragment 来做吗？似乎应该这样做)。if(savedInstanceState.containsKey(AddActivity_Frag1.F1_TAG)){
frag1 = (AddActivity_Frag1)getFragmentManager().getFragment(savedInstanceState, AddActivity_Frag1.F1_TAG);
}
Activity - 删除了许多希望不相关的东西:
public class AddActivity extends Activity{
// data collection
List<ImageBean> beanList;
// adapter
AddCollectionAdapter adapter;
// ListViewFragment tag
private static final String LVF_TAG = "list fragment tag";
// fragment handles
ListViewFragment listFrag;
// Handles images; LruCache for bitmapes
ImageHandler imageHandler;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_add2);
// Create ImageHandler that holds LruCache
imageHandler = new ImageHandler(this, getFragmentManager());
// Obtain retained List<ImageBean> or create new List<ImageBean>.
RetainedFragment retainFragment = RetainedFragment.findOrCreateRetainFragment(getFragmentManager());
beanList = retainFragment.list;
if(beanList == null){
beanList = new ArrayList<ImageBean>();
retainFragment.list = beanList;
}
// create fragments
if(savedInstanceState == null){
listFrag = new ListViewFragment();
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.add(R.id.add_fragFrame, listFrag, LVF_TAG);
ft.commit();
}else{
listFrag = (ListViewFragment)getFragmentManager().findFragmentByTag(LVF_TAG);
}
// create adapter
adapter = new AddCollectionAdapter(this, beanList);
// set list fragment adapter
listFrag.setListAdapter(adapter);
}
@Override
protected void onStart() {
// TESTING: If device orientation has changed List<ImageBean> was saved
// with a RetainedFragment. Seed the adapter with the retained
// List.
adapter.notifyDataSetChanged();
super.onStart();
}
@Override
protected void onSaveInstanceState(Bundle outState) {
// Android automatically saves visible fragments here. (?)
super.onSaveInstanceState(outState);
}
/*
* ImageBean.
*/
public static class ImageBean{
private String collectionName; // Title of image collection
private String imageUri; // Image URI as a string
private String imageTitle; // Title given to image
public ImageBean(String name, String uri, String title){
collectionName = name;
imageUri = uri;
imageTitle = title;
}
public String getCollectionName() {
return collectionName;
}
public String getImageUri() {
return imageUri;
}
public String getImageTitle() {
return imageTitle;
}
}
/*
* Called when user is finished selecting images.
*
* Performs a bulk insert to the Provider.
*/
private void saveToDatabase() {
int arraySize = beanList.size();
final ContentValues[] valuesArray = new ContentValues[arraySize];
ContentValues values;
String imageuri;
String title;
int counter = 0;
for(ImageBean image : beanList){
imageuri = image.getImageUri();
title = image.getImageTitle();
values = new ContentValues();
values.put(CollectionsTable.COL_NAME, nameOfCollection);
values.put(CollectionsTable.COL_IMAGEURI, imageuri);
values.put(CollectionsTable.COL_TITLE, title);
values.put(CollectionsTable.COL_SEQ, counter +1);
valuesArray[counter] = values;
counter++;
}
AsyncTask<Void, Void, Void> task = new AsyncTask<Void, Void, Void>() {
@Override
protected Void doInBackground(Void... arg0) {
getContentResolver().bulkInsert(CollectionsContentProvider.COLLECTIONS_URI, valuesArray);
return null;
}
@Override
protected void onPostExecute(Void result) {
// End this activity.
finish();
}
};
task.execute();
}
public ImageHandler getImageHandler(){
return imageHandler;
}
}
class RetainedFragment extends Fragment{
private static final String TAG = "RetainedFragment";
// data to retain
public List<AddActivity.ImageBean> list;
public static RetainedFragment findOrCreateRetainFragment(FragmentManager fm){
RetainedFragment fragment = (RetainedFragment)fm.findFragmentByTag(TAG);
if(fragment == null){
fragment = new RetainedFragment();
fm.beginTransaction().add(fragment, TAG);
}
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setRetainInstance(true);
}
}
列表 fragment :
public class ListViewFragment extends ListFragment {
ListFragListener listener;
public interface ListFragListener{
public void listFragListener(Cursor cursor);
}
@Override
public void onCreate(Bundle savedInstanceState) {
// Retain this fragment across configuration change
setRetainInstance(true);
super.onCreate(savedInstanceState);
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
// Set listener
if(activity instanceof ListFragListener){
listener = (ListFragListener)activity;
}else{
//Instantiating activity does not implement ListFragListener.
}
}
@Override
public void onListItemClick(ListView listView, View v, int position, long id) {
// no action necessary
}
}
适配器:
public class AddCollectionAdapter extends BaseAdapter {
// data collection
List<ImageBean> beanList;
// layout inflator
private LayoutInflater inflater;
// context
Context context;
public AddCollectionAdapter(Context context, List<ImageBean> beanList){
this.context = context;
this.beanList = beanList;
inflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
@Override
public int getCount() {
return beanList.size();
}
@Override
public Object getItem(int position) {
return beanList.get(position);
}
@Override
public long getItemId(int arg0) {
// collection not from database nor is going directly to database; this is useless.
return 0;
}
// holder pattern
private class ViewHolder{
ImageView imageView;
TextView titleView;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
View xmlTemplate = convertView;
if(xmlTemplate == null){
//inflate xml
xmlTemplate = inflater.inflate(R.layout.frag_listview_row, null);
// initilaize ViewHolder
holder = new ViewHolder();
// get views that are inside the xml
holder.imageView = (ImageView)xmlTemplate.findViewById(R.id.add_lvrow_image);
holder.titleView = (TextView)xmlTemplate.findViewById(R.id.add_lvrow_title);
// set tag
xmlTemplate.setTag(holder);
}else{
holder = (ViewHolder)xmlTemplate.getTag();
}
// Get image details from List<ImageBean>
ImageBean bean = beanList.get(position);
String imageUri = bean.getImageUri();
String title = bean.getImageTitle();
// Set Holder ImageView bitmap; Use parent activity's ImageHandler to load image into Holder's ImageView.
((AddActivity)context).getImageHandler().loadBitmap(imageUri, holder.imageView, Constants.LISTVIEW_XML_WIDTH, Constants.LISTVIEW_XML_HEIGHT);
// Set Holder's TextView.
holder.titleView.setText(title);
// return view
return xmlTemplate;
}
}
最佳答案
解决了。在将日志语句放在重要位置后，我发现 RetainedFragment 的列表始终为空。在 RetainedFragment 中挠头后注意到了这一点:
fm.beginTransaction().add(fragment, TAG);
我错过了
commit() ! 在我添加状态现在正在保留配置更改之后。
我在试验和磨难中发现的与保存 ListFragment 状态相关的更多信息:
如果您通过以下方式添加 fragment :
if(savedInstanceState == null){
listFrag = new ListViewFragment();
// programmatically add fragment to ViewGroup
FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.add(R.id.add_fragFrame, listFrag, LVF_TAG);
}
然后这些中的任何一个都可以在
else 中使用。 :1) This one works because Android takes care of saving the Fragment:
listFrag = (ListViewFragment)getFragmentManager().findFragmentByTag(LVF_TAG);
2) This one works because the fragment was specifically saved into bundle in
onSaveInstanceState:
listFrag = (ListViewFragment)getFragmentManager().getFragment(savedInstanceState, LVF_TAG);
要使 2 号起作用，这发生在 onSaveInstanceState() 中:
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
getFragmentManager().putFragment(outState, LVF_TAG, listFrag);
}
关于android - 如何通过方向更改保存自定义 ListFragment 状态，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/25730163/