出现错误:java.lang.ClassCastException: android.app.Application cannot be cast to android.app.Activity
当尝试在 AsyncTask 的 onPostExecute() 中填充 ListView 时。
为什么我会收到这个？
Activity
public class NotificationsActivity extends Activity {
private static final String FILENAME_NOTIFICATIONS = "notifications.json";
ListView listView;
NotificationsAdapter adapter;
private JSONReader reader;
private ArrayList<Notification> notificationsArray;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_notifications);
getActionBar().setTitle("");
reader = new JSONReader(getApplicationContext());
notificationsArray = new ArrayList<Notification>();
listView = (ListView)findViewById(R.id.notifications_listview);
if (Utilities.isNetworkAvailable(getApplicationContext())) {
new UpdateNotifications().execute();
}
else {
Toast.makeText(getApplicationContext(), "Network Error: No Connectivity", Toast.LENGTH_SHORT).show();
if (Utilities.checkIfFileExists(getApplicationContext(), FILENAME_NOTIFICATIONS)) {
createNotificationsArray();
}
else {
Toast.makeText(getApplicationContext(), "No files found locally. Please connect to the internet and try again.", Toast.LENGTH_LONG).show();
}
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.notifications, menu);
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.action_update:
if (Utilities.isNetworkAvailable(this)) {
new UpdateNotifications().execute();
}
else {
Toast.makeText(getApplicationContext(), "Network Error: No Connectivity", Toast.LENGTH_SHORT).show();
}
return true;
default:
return super.onOptionsItemSelected(item);
}
}
private void createNotificationsArray() {
try {
reader.readFromInternal(FILENAME_NOTIFICATIONS);
notificationsArray = reader.getNotificationsArray();
}
catch (IOException e) { e.printStackTrace(); }
}
private class UpdateNotifications extends AsyncTask<Void, Void, Void> {
ProgressDialog progressDialog;
protected void onPreExecute() {
progressDialog = new ProgressDialog(NotificationsActivity.this);
progressDialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
progressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
progressDialog.setMessage("Updating notifications. Please wait.");
progressDialog.show();
progressDialog.setCanceledOnTouchOutside(false);
}
protected Void doInBackground(Void... params) {
HTTPGetRequest getRequest = new HTTPGetRequest();
JSONWriter writer = new JSONWriter(getApplicationContext());
// Updates local JSON file containing notifications
String notificationsJsonString = "";
notificationsJsonString = getRequest.getNotifications();
try { writer.writeToInternal(FILENAME_NOTIFICATIONS, notificationsJsonString); }
catch (IOException e) { e.printStackTrace(); }
createNotificationsArray();
Log.v("SIZE", Integer.toString(notificationsArray.size()));
return null;
}
protected void onPostExecute(Void result) {
super.onPostExecute(result);
progressDialog.dismiss();
listView = (ListView)findViewById(R.id.notifications_listview);
adapter = new NotificationsAdapter(getApplicationContext(), R.layout.listview_notification_row, notificationsArray);
listView.setAdapter(adapter);
return;
}
}
数组适配器
public class NotificationsAdapter extends ArrayAdapter<Notification> {
private Context context;
private int layoutResourceId;
private ArrayList<Notification> notifications;
public NotificationsAdapter(Context context, int layoutResourceId, ArrayList<Notification> notifications) {
super(context, layoutResourceId, notifications);
this.context = context;
this.layoutResourceId = layoutResourceId;
this.notifications = notifications;
}
private static class ViewHolder {
private TextView notifyName;
private TextView checklist;
private TextView stepName;
private TextView note;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder;
if (convertView == null) {
LayoutInflater inflater = ((Activity) context).getLayoutInflater();
convertView = inflater.inflate(layoutResourceId, parent, false);
holder = new ViewHolder();
holder.notifyName = (TextView)convertView.findViewById(R.id.notify_name);
holder.checklist = (TextView)convertView.findViewById(R.id.checklist_name);
holder.stepName = (TextView)convertView.findViewById(R.id.step_name);
holder.note = (TextView)convertView.findViewById(R.id.notification_note);
convertView.setTag(holder);
}
else {
holder = (ViewHolder)convertView.getTag();
}
String notifyName = notifications.get(position).getNotifyName();
String checklist = notifications.get(position).getChecklist();
String stepName = notifications.get(position).getStepName();
String note = notifications.get(position).getNote();
holder.notifyName.setText(notifyName);
holder.checklist.setText(checklist);
holder.stepName.setText(stepName);
holder.note.setText(note);
return convertView;
}
堆栈跟踪
02-04 21:13:01.713: E/AndroidRuntime(30652): java.lang.ClassCastException: android.app.Application cannot be cast to android.app.Activity
02-04 21:13:01.713: E/AndroidRuntime(30652): at com.medusa.checkit.android.NotificationsAdapter.getView(NotificationsAdapter.java:38)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.widget.AbsListView.obtainView(AbsListView.java:2453)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.widget.ListView.makeAndAddView(ListView.java:1775)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.widget.ListView.fillDown(ListView.java:678)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.widget.ListView.fillFromTop(ListView.java:739)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.widget.ListView.layoutChildren(ListView.java:1628)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.widget.AbsListView.onLayout(AbsListView.java:2288)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.view.View.layout(View.java:13957)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.view.ViewGroup.layout(ViewGroup.java:4374)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1655)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1513)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.widget.LinearLayout.onLayout(LinearLayout.java:1426)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.view.View.layout(View.java:13957)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.view.ViewGroup.layout(ViewGroup.java:4374)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.widget.FrameLayout.onLayout(FrameLayout.java:448)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.view.View.layout(View.java:13957)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.view.ViewGroup.layout(ViewGroup.java:4374)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1655)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1513)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.widget.LinearLayout.onLayout(LinearLayout.java:1426)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.view.View.layout(View.java:13957)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.view.ViewGroup.layout(ViewGroup.java:4374)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.widget.FrameLayout.onLayout(FrameLayout.java:448)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.view.View.layout(View.java:13957)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.view.ViewGroup.layout(ViewGroup.java:4374)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2003)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1824)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1119)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4553)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.view.Choreographer.doCallbacks(Choreographer.java:555)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.view.Choreographer.doFrame(Choreographer.java:525)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.os.Handler.handleCallback(Handler.java:615)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.os.Handler.dispatchMessage(Handler.java:92)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.os.Looper.loop(Looper.java:137)
02-04 21:13:01.713: E/AndroidRuntime(30652): at android.app.ActivityThread.main(ActivityThread.java:4950)
02-04 21:13:01.713: E/AndroidRuntime(30652): at java.lang.reflect.Method.invokeNative(Native Method)
02-04 21:13:01.713: E/AndroidRuntime(30652): at java.lang.reflect.Method.invoke(Method.java:511)
02-04 21:13:01.713: E/AndroidRuntime(30652): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1004)
02-04 21:13:01.713: E/AndroidRuntime(30652): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:771)
02-04 21:13:01.713: E/AndroidRuntime(30652): at dalvik.system.NativeStart.main(Native Method)
最佳答案
在适配器的 getView() 中，更改此代码
LayoutInflater inflater = ((Activity) context).getLayoutInflater();
到
LayoutInflater inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
关于android - 尝试在 AsyncTask 中填充 ListView 时出现 ClassCastException，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/21569159/