（对不起，我不知道我的英文是否正确，我希望它是对的！）loadInBackground（）方法，（在BookLoader类中）返回一个字符串值，但是对谁来说？我找了谁调用了loadInBackground（），但是没有人这样做。我也阅读了官方文档，但没有解决方案。谢谢朋友们的建议。
public class MainActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<String> {
public EditText mEditText;
public TextView mTextTitle, mTextAuthor;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mEditText = (EditText) findViewById(R.id.bookInput);
mTextTitle = (TextView) findViewById(R.id.titleText);
mTextAuthor = (TextView) findViewById(R.id.authorText);
// to reconnect to the Loader if it already exists
if(getSupportLoaderManager().getLoader(0)!=null){
getSupportLoaderManager().initLoader(0,null,this);
}
}
public void searchBooks(View view) {
String queryString = mEditText.getText().toString();
// nasconde la tastiera
InputMethodManager inputManager = (InputMethodManager)getSystemService(Context.INPUT_METHOD_SERVICE);
inputManager.hideSoftInputFromWindow(getCurrentFocus().getWindowToken(), InputMethodManager.HIDE_NOT_ALWAYS);
// Check the status of the network connection.
ConnectivityManager connMgr = (ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
if (networkInfo != null && networkInfo.isConnected() && queryString.length()!=0) {
mTextAuthor.setText("");
mTextTitle.setText(R.string.loading);
Bundle queryBundle = new Bundle();
queryBundle.putString("queryString", queryString);
getSupportLoaderManager().restartLoader(0, queryBundle,this);
}
else {
if (queryString.length() == 0) {
mTextAuthor.setText("");
mTextTitle.setText("Please enter a search term");
} else {
mTextAuthor.setText("");
mTextTitle.setText("Please check your network connection and try again.");
}
}
}
// Called when you instantiate your Loader.
@NonNull
@Override
public Loader<String> onCreateLoader(int i, @Nullable Bundle bundle) {
return new BookLoader(this, bundle.getString("queryString"));
}
@Override
public void onLoadFinished(@NonNull Loader<String> loader, String s) {
try {
JSONObject jsonObject = new JSONObject(s);
JSONArray itemsArray = jsonObject.getJSONArray("items");
int i = 0;
String title = null;
String authors = null;
while (i < itemsArray.length() || (authors == null && title == null)) {
// Get the current item information.
JSONObject book = itemsArray.getJSONObject(i);
JSONObject volumeInfo = book.getJSONObject("volumeInfo");
// Try to get the author and title from the current item,
// catch if either field is empty and move on.
try {
title = volumeInfo.getString("title");
authors = volumeInfo.getString("authors");
Log.d("TITLE", volumeInfo.getString("title"));
} catch (Exception e){
e.printStackTrace();
}
// Move to the next item.
i++;
}
// If both are found, display the result.
if (title != null && authors != null){
mTextTitle.setText(title);
mTextAuthor.setText(authors);
mEditText.setText("");
} else {
// If none are found, update the UI to show failed results.
mTextTitle.setText("no results");
mTextAuthor.setText("");
}
} catch (Exception e){
// If onPostExecute does not receive a proper JSON string, update the UI to show failed results.
mTextTitle.setText("no results");
mTextAuthor.setText("");
e.printStackTrace();
}
}
// Cleans up any remaining resources.
@Override
public void onLoaderReset(@NonNull Loader<String> loader) {
}
}
public class BookLoader extends AsyncTaskLoader<String> {
String mQueryString;
public BookLoader(@NonNull Context context, String queryString) {
super(context);
mQueryString = queryString;
}
@Nullable
@Override
public String loadInBackground() {
return NetworkUtils.getBookInfo(mQueryString);
}
@Override
protected void onStartLoading() {
super.onStartLoading();
forceLoad();
}
}
我编辑了这篇文章。
正如官方文件所说：
onPostExecute（Result），在后台计算完成后在UI线程上调用。背景计算的结果作为参数传递给该步骤。
您的返回值将发送到onPostExecute（）。
我鼓励你深入了解this documentation