[英]App crashing while trying to display a Toast on AlertDialog button click (in a Fragment)
我正在嘗試使DialogFragment包含警報對話框。 它包含一個接口,該接口包含一個應在按下對話框的“取消/確定”按鈕時調用的方法。
現在的問題是,我想在用戶單擊“確定” /“取消”時顯示Toast.makeText,但是我不知道應該傳遞給Toast的上下文是什么,以免崩潰。 當用戶單擊對話框按鈕時,我的應用程序崩潰了,我猜是上下文導致了異常:
片段類:
public class AlertDFragment extends DialogFragment {
dialogListener ds;
Context con;
public interface dialogListener {
public void onOK(Context c);
public void onCancel(Context c);
}
@Override
public Dialog onCreateDialog(Bundle savedInstances) {
Builder b = new AlertDialog.Builder(getActivity());
b.setIcon(R.drawable.abc_ic_search);
b.setTitle("DialogFragment instance");
b.setMessage("Choose an option");
b.setPositiveButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
ds.onOK(con);
}
});
b.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface arg0, int arg1) {
ds.onCancel(con);
}
});
return b.create();
}
public AlertDFragment() {
}
protected void OnAttach(Activity activity) {
super.onAttach(activity);
con = activity;
try {
ds = (dialogListener) activity;
} catch(ClassCastException e) {
throw new ClassCastException(activity.toString()+" must implement the dialogListener interface");
}
}
}
主要活動(片段的父對象):
public class MainActivity extends FragmentActivity implements AlertDFragment.dialogListener {
Button dialog2;
FragmentManager fm = getSupportFragmentManager();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dialog2 = (Button) findViewById(R.id.btn2);
dialog2.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View arg0) {
AlertDFragment adf = new AlertDFragment();
adf.show(fm, "MY TAG");
}
});
}
//interface methods
public void onOK(Context c) {
Toast.makeText(MainActivity.this, "OK pressed", Toast.LENGTH_SHORT).show();
}
public void onCancel(Context c) {
Toast.makeText(MainActivity.this, "Cancel pressed", Toast.LENGTH_SHORT).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.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
和LogCat:
11-04 10:23:30.959: E/AndroidRuntime(2014): FATAL EXCEPTION: main
11-04 10:23:30.959: E/AndroidRuntime(2014): Process: com.apex.dialogtest, PID: 2014
11-04 10:23:30.959: E/AndroidRuntime(2014): java.lang.NullPointerException
11-04 10:23:30.959: E/AndroidRuntime(2014): at com.apex.dialogtest.AlertDFragment$1.onClick(AlertDFragment.java:33)
11-04 10:23:30.959: E/AndroidRuntime(2014): at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:166)
11-04 10:23:30.959: E/AndroidRuntime(2014): at android.os.Handler.dispatchMessage(Handler.java:102)
11-04 10:23:30.959: E/AndroidRuntime(2014): at android.os.Looper.loop(Looper.java:136)
11-04 10:23:30.959: E/AndroidRuntime(2014): at android.app.ActivityThread.main(ActivityThread.java:5017)
11-04 10:23:30.959: E/AndroidRuntime(2014): at java.lang.reflect.Method.invokeNative(Native Method)
11-04 10:23:30.959: E/AndroidRuntime(2014): at java.lang.reflect.Method.invoke(Method.java:515)
11-04 10:23:30.959: E/AndroidRuntime(2014): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
11-04 10:23:30.959: E/AndroidRuntime(2014): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
11-04 10:23:30.959: E/AndroidRuntime(2014): at dalvik.system.NativeStart.main(Native Method)
提前致謝!
ds
未初始化,因為protected void OnAttach(Activity activity)
需要小寫的o。 確保始終使用@Override注釋,否則會出現錯誤。
您在代碼中具有以下內容
dialogListener ds;
但是您永遠不會實例化它。 然后調用ds.onOK(con);
參考ds
上的方法。 這將導致空指針異常。
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