当这两个Toasts位于片段内部的AsyncTask内部时会导致崩溃,当我删除两个Toast时,一切正常,没有崩溃。为什么是这样?如何在AsyncTask中使用Toast消息而不会导致崩溃?
Toast.makeText(activity, "onPostExecute", Toast.LENGTH_LONG).show();
Toast.makeText(activity,"onPreExecute", Toast.LENGTH_LONG).show();
Logcat显示toast消息的nullPointerException。当我删除两个吐司中的第一个它将运行然后崩溃,当第一个吐司在那里它将在开始时崩溃,当两个吐司被移除时它永远不会崩溃。
代码的其余部分
public class FragmentStaticFragment extends Fragment {
private Button buttonStartProgress;
private ProgressBar progressBar;
Activity activity = getActivity();
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_static_fragment, container, false);
buttonStartProgress = (Button) view.findViewById(R.id.button1);
progressBar = (ProgressBar) view.findViewById(R.id.progressBar1);
buttonStartProgress.setOnClickListener(new Button.OnClickListener(){
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
new BackgroundAsyncTask().execute();
buttonStartProgress.setClickable(false);
}
});
return view;
}
public class BackgroundAsyncTask extends AsyncTask<Void, Integer, Void>{
int myProgress;
@Override
protected void onPostExecute(Void result) {
// TODO Auto-generated method stub
// commented out this toast to avoid crashing
// Toast.makeText(activity, "onPostExecute", Toast.LENGTH_LONG).show();
buttonStartProgress.setClickable(true);
}
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
// commented out this toast to avoid crashing
// Toast.makeText(activity,"onPreExecute", Toast.LENGTH_LONG).show();
myProgress = 0;
}
@Override
protected Void doInBackground(Void... params) {
// TODO Auto-generated method stub
while(myProgress<100){
myProgress++;
publishProgress(myProgress);
SystemClock.sleep(100);
}
return null;
}
@Override
protected void onProgressUpdate(Integer... values) {
// TODO Auto-generated method stub
progressBar.setProgress(values[0]);
}
} // end BackgroundAsyncTask
}
EDIT;
添加了堆栈跟踪信息
07-13 09:23:01.383: E/AndroidRuntime(19489): FATAL EXCEPTION: main
07-13 09:23:01.383: E/AndroidRuntime(19489): java.lang.NullPointerException
07-13 09:23:01.383: E/AndroidRuntime(19489): at android.widget.Toast.<init>(Toast.java:92)
07-13 09:23:01.383: E/AndroidRuntime(19489): at Android.widget.Toast.makeText(Toast.java:233)
07-13 09:23:01.383: E/AndroidRuntime(19489): at com.example.asynctaskprogressbarexample.FragmentStaticFragment$BackgroundAsyncTask.onPreExecute(FragmentStaticFragment.java:62)
07-13 09:23:01.383: E/AndroidRuntime(19489): at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:561)
07-13 09:23:01.383: E/AndroidRuntime(19489): at android.os.AsyncTask.execute(AsyncTask.java:511)
07-13 09:23:01.383: E/AndroidRuntime(19489): at com.example.asynctaskprogressbarexample.FragmentStaticFragment$1.onClick(FragmentStaticFragment.java:36)
答案 0 :(得分:3)
getActivity()
之前运行, null
将返回onAttach(Activity)
。相反,您应该直接在getActivity()
和onPreExecute
方法中调用onPostExecute
,或在onAttach
中获取对它的引用:
public void onAttach (Activity attachedActivity) {
activity = attachedActivity;
}