无法使用 adapterName.clear() 清除 ArrayAdapter 中的数据

Question

我正在使用PreferenceFragment，我希望每次更改PreferenceScreen's widget的值时，结果都应根据ListView中的值显示。一切都运行正常，除非我更改任何PreferenceScreen's widget的值，而不是在ListView中向我显示一个新列表，而是在同一列表中添加值。显然，adapter.clear()不起作用。

谁能建议如何使其工作？

这是我的主要活动：

public class MainActivity extends AppCompatActivity implements 
LoaderManager.LoaderCallbacks<String>, 
SharedPreferences.OnSharedPreferenceChangeListener{
private static final String TAG = "MainActivity";
private static final int LOADER_INIT_KEY = 0;
EditText titleTextView;
Button searchButton;
ListView listView;

String query = "";
private ArrayList<String> authorsList = new ArrayList<>();
private ArrayList<BooksDetails> booksDetails = new ArrayList<>();
private String title = null, id = null;
private CustomAdapter adapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main_layout);
titleTextView = findViewById(R.id.author_textView);
searchButton = findViewById(R.id.search);
listView = findViewById(R.id.list_view);
/**
* this declaration is needed
*/
adapter = new CustomAdapter(this, new ArrayList<BooksDetails>());
final ListView listView = findViewById(R.id.list_view_in_main_layout);
listView.setAdapter(adapter);
// getting instance of SharedPreference and attaching listener to it
SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
//  any change in the SharedPreference will get notified
//  if user tweaks any settings
sharedPreferences.registerOnSharedPreferenceChangeListener(this);
//  Search button
searchButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//  getting value from textView
query = titleTextView.getText().toString();
Log.d(TAG, "onClick: "+query);
//  clearing the adapter
adapter.clear();
//  checking the network connection
ConnectivityManager connectivityManager = (ConnectivityManager)getSystemService(CONNECTIVITY_SERVICE);
assert connectivityManager != null;
NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();
if(networkInfo != null && networkInfo.isConnected()) {
if(query.length() != 0) {
getSupportLoaderManager().initLoader(LOADER_INIT_KEY, null, MainActivity.this);
closeKeyboard();
Log.d(TAG, "onClick: ");
}
else
Toast.makeText(MainActivity.this, "Enter a title", Toast.LENGTH_SHORT).show();
}
else{
Toast.makeText(MainActivity.this, "Not connected to internet", Toast.LENGTH_SHORT).show();
}
}
});
}
private void closeKeyboard(){
//  hiding keyboard after the search
InputMethodManager inputMethodManager = (InputMethodManager)getSystemService(Context.INPUT_METHOD_SERVICE);
View focusedView = this.getCurrentFocus();
if(focusedView != null) {
try {
assert inputMethodManager != null;
inputMethodManager.hideSoftInputFromWindow(focusedView.getWindowToken(), InputMethodManager.HIDE_NOT_ALWAYS);
}catch (AssertionError e){
Log.e(TAG, "closeKeyboard: Assertion error is thrown inputMethodManager is null", e);
}
}
}
@NonNull
@Override
public android.support.v4.content.Loader onCreateLoader(int id, @Nullable Bundle args) {
Log.d(TAG, "onCreateLoader: ");
//  getting the SharedPreference which contains all the values of the Preference
//  SharedPreference for maxResults
SharedPreferences maxResultsSharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
String maxResults = maxResultsSharedPreferences.getString(getString(R.string.settings_default_result_key),
getString(R.string.settings_default_value_of_result));
//  SharedPreference for OrderBy
SharedPreferences orderBySharedPreference = PreferenceManager
.getDefaultSharedPreferences(this);
String orderByValue = orderBySharedPreference.getString(getString(R.string.settings_order_by_key),
getString(R.string.settings_order_by_default));

//  passing the minResults with query
return new CustomLoader(this, query, maxResults, orderByValue);
}

@Override
public void onLoadFinished(@NonNull android.support.v4.content.Loader loader, String s) {
Log.d(TAG, "onLoadFinished: ");
//  clearing the adapter
adapter.clear();
//  after getting the raw json we are parsing it here
try {
JSONObject rootObject = new JSONObject(s);
JSONArray itemsArray = rootObject.getJSONArray("items");
for(int i = 0;i < itemsArray.length();i++){
//  getting each object in the array itemsArray
JSONObject booksInfo = itemsArray.getJSONObject(i);
//  getting book id
id = booksInfo.getString("id");
//  getting the volumeInfo object
JSONObject volumeInfo = booksInfo.getJSONObject("volumeInfo");
//  getting title of the book
title = volumeInfo.getString("title");
//  getting the author
JSONArray author = volumeInfo.getJSONArray("authors");
//  getting all the members of author array
for(int j = 0;j < author.length();j++){
authorsList.add(author.getString(j));
}
if(title == null) {
//  if no title matches
titleTextView.setText("No title matches");
}
//   adding details in the ArrayList bookDetails
booksDetails.add(new BooksDetails(id, title, authorsList.get(0)));
}
adapter.addAll(booksDetails);
}
catch(Exception e){
Log.e(TAG, "onLoadFinished: exception in json parsing", e);
}
}
@Override
public void onLoaderReset(@NonNull android.support.v4.content.Loader loader) {
Log.d(TAG, "onLoaderReset: ");
//  clearing the adapter
adapter.clear();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.settings_menu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
if(item.getItemId() == R.id.action_settings){
Intent intent = new Intent(this, SettingsActivity.class);
startActivity(intent);
}
return super.onOptionsItemSelected(item);
}
@Override
public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
Log.d(TAG, "onSharedPreferenceChanged: ");
if(key.equals(getString(R.string.settings_order_by_key)) || key.equals(getString(R.string.settings_default_result_key))){
//  clearing the adapter
adapter.clear();
getSupportLoaderManager().restartLoader(LOADER_INIT_KEY, null, this);
}
}
@Override
protected void onRestart() {
super.onRestart();
adapter.clear();
}

}

Answer 1

您需要重置已传递给适配器的源列表。 因为您将初始代码放在 onCreate 方法中，该方法在创建活动时已调用过一次。

而不是adapter = new CustomAdapter(this, new ArrayList<BooksDetails>());

试试这个：

CustomAdapter adapter;
List<BooksDetails> srcList;
public void onCreate() {
srcList = new ArrayList<BookDetails>();
adapter = new CustomAdapter(this, srcList);
}

当您需要清除适配器时，请尝试此操作

srcList().clear();
adapter.clear();
adapter.notifyDatasetChanged();