我有一个导航菜单，上面有导航菜单。单击每个导航菜单时，将打开特定片段。例如，当我单击单词导航菜单时，单词项目会显示recyclerView个项目。我从离线和外部SQLite数据库中获取数据并显示在recyclerView项目上。现在我想在另一个线程中获取数据，而不是在主线程中，因为我想提高加载速度数据和应用程序性能。但我不知道该怎么做。请帮我一个代码。我在互联网上阅读了相同的主题，但我现在仍然有我的问题。
这是我的 AllWordsFragment
public class AllWordsFragment extends Fragment {
private List<WordsList> wordsLists = new ArrayList<>();
private Cursor cursor;
ProgressBar progressBar;
RecyclerView recyclerView;
AllWordsAdapter allWordsAdapter;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater,
@Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.all_words_fragment, container, false);
progressBar = view.findViewById(R.id.progressBar);
progressBar.setMax(600);
allWordsAdapter = new AllWordsAdapter(getActivity(), wordsLists);
allWordsAdapter.notifyDataSetChanged();
recyclerView = view.findViewById(R.id.recyclerViewAllWords);
RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getActivity());
recyclerView.setLayoutManager(layoutManager);
recyclerView.setItemAnimator(new DefaultItemAnimator());
recyclerView.setHasFixedSize(true);
recyclerView.setAdapter(allWordsAdapter);
loadingWords();
return view;
}
private void loadingWords() {
WordDatabase wordDatabase = new WordDatabase(getActivity());
try {
wordDatabase.createDatabase();
wordDatabase.openDatabase();
} catch (SQLiteException e) {
e.printStackTrace();
}
try {
cursor = wordDatabase.QueryData("SELECT Word, Definition, Example, WordList, ImageWord FROM Words");
if (cursor != null && cursor.moveToFirst()) {
do {
WordsList wordList = new WordsList();
wordList.setWordTitle(cursor.getString(0));
wordList.setDefinition(cursor.getString(1));
wordList.setExample(cursor.getString(2));
wordList.setVocubList(cursor.getString(3));
wordList.setImageWord(cursor.getString(4));
wordsLists.add(wordList);
} while (cursor.moveToNext());
wordDatabase.close();
}
} catch (SQLiteException w) {
w.printStackTrace();
} finally {
if (cursor != null) {
cursor.close();
}
}
}
这是我的 AllWordsAdapter
公共类AllWordsAdapter扩展了RecyclerView.Adapter {
private int lastPosition = -1;
protected Context context;
private List<WordsList> wordsListList = new ArrayList<>();
public AllWordsAdapter(Context context, List<WordsList> wordsListList) {
this.context = context;
this.wordsListList = wordsListList;
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(context).inflate(R.layout.all_words_item, parent, false);
return new ViewHolder(view);
}
@Override
public void onBindViewHolder(final ViewHolder holder, int position) {
WordsList wordsList = wordsListList.get(position);
holder.wordTitle.setText(wordsList.getWordTitle());
holder.definitionWord.setText(Html.fromHtml(wordsList.getDefinition()));
holder.exampleWord.setText(Html.fromHtml(wordsList.getExample()));
holder.labelWordList.setLabelText(wordsList.getVocubList());
//get image from assets with Glide.
String pathImage = wordsList.getImageWord();
String assetsPath = "file:///android_asset/";
Glide.with(context)
.asBitmap()
.load(Uri.parse(assetsPath + "" + pathImage))
.into(holder.wordImage);
Log.d("path", assetsPath + "" + pathImage);
Typeface headerFont = Typeface.createFromAsset(context.getAssets(), "fonts/Roboto-Bold.ttf");
holder.wordTitle.setTypeface(headerFont);
Typeface customFont = Typeface.createFromAsset(context.getAssets(), "fonts/Roboto-Italic.ttf");
holder.exampleWord.setTypeface(customFont);
holder.definitionWord.setTypeface(customFont);
//cal animation function
setAnimation(holder.itemView, position);
holder.relativeLayout.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent(context, AllWordsDetails.class);
intent.putExtra("word", holder.wordTitle.getText().toString());
context.startActivity(intent);
}
});
}
@Override
public int getItemCount() {
return wordsListList.size();
}
public class ViewHolder extends RecyclerView.ViewHolder {
private CircleImageView wordImage;
private LabelTextView labelWordList;
private TextView wordTitle, definitionWord, exampleWord;
private RelativeLayout relativeLayout;
public ViewHolder(View itemView) {
super(itemView);
wordTitle = itemView.findViewById(R.id.allWordTitle);
wordImage = itemView.findViewById(R.id.circleHeaderImage);
exampleWord = itemView.findViewById(R.id.exampleAllWord);
definitionWord = itemView.findViewById(R.id.definitionAllWord);
labelWordList = itemView.findViewById(R.id.labelWordList);
relativeLayout = itemView.findViewById(R.id.relativeAllWords);
}
}
private void setAnimation(View viewToAnimation, int position) {
// If the bound view wasn't previously displayed on screen, it's animated
if (position > lastPosition) {
ScaleAnimation scaleAnimation = new ScaleAnimation(0.0f, 1.0f, 0.0f, 1.0f,
Animation.RELATIVE_TO_SELF, 0.5f, Animation.RELATIVE_TO_SELF, 0.5f);
scaleAnimation.setDuration(new Random().nextInt(501));//to make duration random number between [0,501)
viewToAnimation.startAnimation(scaleAnimation);
lastPosition = position;
}
}
}
我知道必须使用 AsyncTask 并在后台执行此操作，但我不知道这是怎么做到的？请帮我一个代码。 谢谢。
答案 0 :(得分：3)
在类中创建一个AsyncTask类：
class WordLoaderTask extends AsyncTask<Void, Void, Void> {
protected Void doInBackground(Void... params) {
loadingWords();
}
protected void onPostExecute(Void param) {
allWordsAdapter.notifyDataSetChanged();
}
}//asyncClass
使用以下行替换loadingWords()中的调用onCreate()：
new WordLoaderTask().execute();
如果您（由于某种原因或某种方式使用应用）开始在ListView中获取重复项，请在wordsLists.clear();方法{/ 1}中的第一行添加do{}
答案 1 :(得分：0)
Try like this
public class AllWordsFragment extends Fragment {
private List<WordsList> wordsLists = new ArrayList<>();
private Cursor cursor;
ProgressBar progressBar;
RecyclerView recyclerView;
AllWordsAdapter allWordsAdapter;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater,
@Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.all_words_fragment, container, false);
progressBar = view.findViewById(R.id.progressBar);
progressBar.setMax(600);
allWordsAdapter = new AllWordsAdapter(getActivity(), wordsLists);
allWordsAdapter.notifyDataSetChanged();
recyclerView = view.findViewById(R.id.recyclerViewAllWords);
RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getActivity());
recyclerView.setLayoutManager(layoutManager);
recyclerView.setItemAnimator(new DefaultItemAnimator());
recyclerView.setHasFixedSize(true);
recyclerView.setAdapter(allWordsAdapter);
loadingWords();
return view;
}
private static LoadWordsTask extends AsyncTask<Void, Void, List<WordsList>> {
private Context context;
private AllWordsAdapter adapter;
private List<WordsList> wordsLists;
public LoadWordsTask(Context context, AllWordsAdapter adapter, List<WordsList> wordsLists) {
this.context = context;
this.adapter = adapter;
this.wordsLists = wordsLists;
}
@Override
public List<WordsList> doInBackground() {
List<WordsList> data = new ArrayList<>();
WordDatabase wordDatabase = new WordDatabase(getActivity());
try {
wordDatabase.createDatabase();
wordDatabase.openDatabase();
} catch (SQLiteException e) {
e.printStackTrace();
}
try {
cursor = wordDatabase.QueryData("SELECT Word, Definition, Example, WordList, ImageWord FROM Words");
if (cursor != null && cursor.moveToFirst()) {
do {
WordsList wordList = new WordsList();
wordList.setWordTitle(cursor.getString(0));
wordList.setDefinition(cursor.getString(1));
wordList.setExample(cursor.getString(2));
wordList.setVocubList(cursor.getString(3));
wordList.setImageWord(cursor.getString(4));
data.add(wordList);
} while (cursor.moveToNext());
wordDatabase.close();
}
} catch (SQLiteException w) {
w.printStackTrace();
} finally {
if (cursor != null) {
cursor.close();
}
}
return data;
}
@Override
public void onPostExecute(List<WordsList> data) {
this.wordsLists.addAll(data);
this.adapter.notifyDataSetChanged();
}
}
}