當從互聯網獲取數據時按壓返回時強制關閉

Question

每當用戶按下返回按鈕使用AsyncTask從Web獲取xml數據時，我的應用程序會強制關閉狀態。我該如何解決這個問題。提前致謝。

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); 

    } 
} 

} 上面的代碼是我更新的代碼。這也有時會顯示異常。在這裏，我已經使用onStop（）和OnDestroy（）來取消AsyncTask，而其他活動最重要。

Answer 1

@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); 
    } 

所以現在當你點擊後退按鈕時，對話框不會消失。

希望爲您提供幫助。

Answer 2

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); 
    } 
    ... 
} 

...