我正在从ListView迁移到RecyclerView，我最后一件事就是更新其中一个字段。我的应用程序有一个简单的列表，在互联网上找到一些图像当您选择一个时，图像会下载到手机以供以后离线查看。适配器从SQLite database获取数据，因此当您点击某个图像时，数据库会更新（文本更改从“点击此处下载”到“已下载”）并且RecyclerView应该遵循。
我遇到与ListView相同的问题，但每次App更新db时我都会调用populateList();。我知道这不是理想的解决方案，但它有效。现在我想用notifyDataSetChanged()或更好notifyItemChanged(position)来做到这一点，但我无法让它发挥作用。
无论如何这里是代码，抱歉有点乱。这只是一个测试代码（RecyclerView代码来自样本）：
public class RecyclerFragment extends Fragment {
private imgAdapter mAdapter;
private DatabaseHandler db;
private ProgressDialog mProgressDialog;
public RecyclerFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
db = new DatabaseHandler(getActivity());
List<Images> listdb = db.getImages();
mAdapter = new ImgAdapter(getActivity(), listdb);
db.close();
View view = inflater.inflate(R.layout.fragment_main, container, false);
RecyclerView recyclerView = (RecyclerView) view.findViewById(android.R.id.list);
recyclerView.addItemDecoration(new DividerItemDecoration(getActivity(), DividerItemDecoration.VERTICAL_LIST));
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new GridLayoutManager(
getActivity(), getResources().getInteger(R.integer.list_columns)));
recyclerView.setAdapter(mAdapter);
return view;
}
private class ImgAdapter extends RecyclerView.Adapter<ViewHolder>
implements ItemClickListener {
public List<Images> mList;
private Context mContext;
public ImgAdapter(Context context, List<Images> listdb) {
super();
mContext = context;
mList = listdb;
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
LayoutInflater inflater = LayoutInflater.from(mContext);
View view = inflater.inflate(R.layout.list_row1, parent, false);
return new ViewHolder(view, this);
}
@Override
public void onBindViewHolder(final ViewHolder holder, final int position) {
Images image = mList.get(position);
holder.mTitle.setText(image.getTitle());
holder.mDownloadStatus.setText(image.getDownloadStatus());
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public int getItemCount() {
return mList == null ? 0 : mList.size();
}
@Override
public void onItemClick(View view, int position) {
switch (position) {
case 0:
Log.v("POSITION 0:", " " + position);
break;
case 1:
/*
some logic nvm
*/
String imgurl = "http:/...";
String imagename = "Second image";
new GetImages(imgurl, imagename).execute();
/*
I've tried mAdapter.notitfy... , no luck aswell
This does nothing:
*/
notifyItemChanged(position);
notifyDataSetChanged();
break;
//....
}
}
}
private static class ViewHolder extends RecyclerView.ViewHolder
implements View.OnClickListener {
TextView mTitle;
TextView mDownloadStatus;
ItemClickListener mItemClickListener;
public ViewHolder(View view, ItemClickListener itemClickListener) {
super(view);
mTitle = (TextView) view.findViewById(R.id.text1);
mDownloadStatus = (TextView) view.findViewById(R.id.text2);
mItemClickListener = itemClickListener;
view.setOnClickListener(this);
}
@Override
public void onClick(View v) {
mItemClickListener.onItemClick(v, getPosition());
}
}
interface ItemClickListener {
void onItemClick(View view, int position);
}
/*
This is my AsyncTask class used for downloading image and updating db
I removed some code just to to make it cleaner
*/
private class GetImages extends AsyncTask<Object, Object, Object> {
private final String requestUrl;
private final String imagename_;
private String imagename;
public int numberofbits;
private GetImages(String requestUrl, String _imagename_) {
this.requestUrl = requestUrl;
this.imagename_ = _imagename_;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
//pDialog...
}
@Override
protected Object doInBackground(Object... objects) {
try {
URL url = new URL(requestUrl);
URLConnection conn = url.openConnection();
bitmap = BitmapFactory.decodeStream(conn.getInputStream());
numberofbits = bitmap.getByteCount();
} catch (Exception ignored) {
}
return null;
}
@Override
protected void onPostExecute(Object o) {
if (!ImageStorage.checkifImageExists(imagename)) {
ImageStorage.saveToSdCard(bitmap, imagename_);
}
if (numberofbits > 50) {
db = new DatabaseHandler(getActivity());
db.updateImages(new Images(dbid, "Downloaded", imagename_));
db.close();
//populateList(); -> THIS I USED FOR A LISTVIEW
Toast.makeText(getActivity(), "Downloaded!", Toast.LENGTH_SHORT).show();
mProgressDialog.dismiss();
//If image gets downloaded open it in Viewer class
Intent intent = new Intent(getActivity(), DisplayImage.class);
intent.putExtra("imagePath", path);
startActivity(intent);
} else {
//Toast.makeText(getActivity(), "Unable to download", Toast.LENGTH_SHORT).show();
mProgressDialog.dismiss();
}
}
}
}
这是Images类
public class Images {
//private variables
private int _id;
private String _title;
private String _downloadstatus;
// Empty constructor
public Images () {
}
// constructor
public Images(int id, String title, String downloadstatus) {
this._id = id;
this._title = title;
this._downloadstatus = downloadstatus;
}
public int getID() {
return this._id;
}
public void setID(int id) {
this._id = id;
}
public String getTitle() {
return this._title;
}
public void setTitle(String title) {
this._title = title;
}
public String getDownloadStatus() {
return this._downloadstatus;
}
public void setDownloadStatus(String downloadstatus) {
this._downloadstatus = downloadstatus;
}
}
这是一个XML（我正在尝试更新“text2”）：
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:foreground="?attr/selectableItemBackground"
android:layout_height="wrap_content"
android:padding="8dp">
<RelativeLayout
android:layout_width="fill_parent"
android:layout_height="match_parent"
>
<TextView
android:id="@+id/text1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="@dimen/imagename"
android:textStyle="bold"
android:paddingStart="4sp"
android:paddingEnd="40sp" />
<TextView
android:id="@+id/text2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@+id/text1"
android:textSize="@dimen/downloaded"
android:paddingStart="4sp"
android:paddingEnd="1sp"
android:textColor="@color/graydownloaded" />
</RelativeLayout>
</FrameLayout>
答案 0 :(得分：1)
尝试这样做：在适配器中覆盖getItemId方法，如下所示
@Override
public long getItemId(int position) {
return mList.get(position).getID();
}
在recyclerView.setHasFixedSize(true)之后添加此行：
recyclerView.setHasStableId(true);
编辑：
mAdapter.setHasStableId(true);
让我知道是否有诀窍。
答案 1 :(得分：1)
好的，我终于开始工作，实际上非常简单......
//....
if (numberofbits > 50) {
db = new DatabaseHandler(getActivity());
db.updateImages(new Images(dbid, "Downloaded", imagename_));
//This is what I added:
List<Images> listdb = db.getImages();
mAdapter = new ImgAdapter(getActivity(), listdb);
recyclerView.setAdapter(mAdapter);
db.close();
//populateList(); -> THIS I USED FOR A LISTVIEW
Toast.makeText(getActivity(), "Downloaded!", Toast.LENGTH_SHORT).show();
mProgressDialog.dismiss();
//If image gets downloaded open it in Viewer class
Intent intent = new Intent(getActivity(), DisplayImage.class);
intent.putExtra("imagePath", path);
startActivity(intent);
} else {
//...