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每当用户按下返回按钮同时使用 AsyncTask 从 Web 获取 xml 数据时，我的应用程序将进入强制关闭状态。我该如何解决这个问题。提前致谢。

public class InboxActivity extends Activity {
public static ExpandableListView mailList;
List<HashMap<String,String>> list;
MailList asyncTaskMailList;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.inbox_layout);
    ConstantValues.footerCurrentActivity=InboxActivity.this;
    mailList=(ExpandableListView)findViewById(R.id.expandableListView1);
    HomePageActivity.homePageTabHost.getTabWidget().getChildTabViewAt(ConstantValues.CURRENT_POSITION)
        .setBackgroundDrawable(getResources().getDrawable(R.drawable.tab_widget_normal));
    asyncTaskMailList=new MailList();
    asyncTaskMailList.execute();
}
private OnChildClickListener childClickListener=new ExpandableListView.OnChildClickListener() {
    public boolean onChildClick(ExpandableListView parent, View v,int groupPosition, int childPosition, long id) {
        ConstantValues.STATION_NAME=ConstantValues.inboxStations.get(groupPosition);
        ConstantValues.CURRENT_POSITION=1;
        startActivity(new Intent(InboxActivity.this, HomePageActivity.class));
        return false;
    }
};
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if(keyCode == KeyEvent.KEYCODE_BACK){
        this.getParent().onBackPressed();
        asyncTaskMailList.cancel(true);
        return true;
    }
    return super.onKeyDown(keyCode, event);
}
@Override
protected void onStop() {
    super.onStop();
    asyncTaskMailList.cancel(true);
}
@Override
protected void onDestroy() {
    asyncTaskMailList.cancel(true);
    super.onDestroy();
}
class MailList extends AsyncTask<String, String, String>
{
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        NetworkExceptionPopUp.showProgressBar();
    }
    @Override
    protected String doInBackground(String... params) {
        list=new ArrayList<HashMap<String,String>>();
        WebServerCall.getInboxMail(InboxActivity.this);
        return null;
    }
    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);
        mailList.setAdapter(new InboxAdapter(InboxActivity.this));
        NetworkExceptionPopUp.dismissProgressBar();
        mailList.setOnGroupClickListener(null);
        mailList.setOnChildClickListener(childClickListener);
        mailList.setClickable(true);

    }
}

上面的代码是我更新的代码。这有时也会显示异常。在这里，我使用 onStop() 和 OnDestroy() 来取消 AsyncTask 而其他活动排在首位。

4

2 回答 2

2 
@Override
    protected void onPreExecute() {
        super.onPreExecute();
        NetworkExceptionPopUp.showProgressBar(); 
       /** add this line to your progressDialog so that diaolg as well your background operation wont stop in intermediate state. */
        // pd.setCancelable(false);
    }

因此，现在当您单击返回按钮时，对话框不会关闭。

希望这对您有所帮助。

于 2013-03-12T06:51:37.000 回答
1 
private MailList task; 

@Override
public void onCreate(Bundle savedInstanceState) {
    ...
    task = new MailList().execute();
    ...
}

@Override
public void onBackPressed() {
    if (task != null && task.getStatus() == AsyncTask.Status.RUNNING) {
        task.cancel(true);
    }
    ...
}

...
于 2013-03-12T06:53:01.977 回答