AsyncTask的取消不工作 [英] AsyncTask Cancel is not working
问题描述
我学习如何取消的AsyncTask所以下面的code无用途。
我试着叫AsyncTask的并执行它，然后取消它，执行它。
MyAsyncTask的AsyncTask =新MyAsyncTask（）;
Log.i（取消，取消1）;
asyncTask.execute（）;
Log.i（取消，取消2）;
asyncTask.onCancelled（）;
Log.i（取消，取消3）;
asyncTask.execute（）;
Log.i（取消，取消DONE）;
取消1和取消2作为logcat的显示，但ActivityThread.performLaunchActivity引发错误时，取消3试图执行被精细地执行。
（取消3 logcat中未显示），任何问题我的AsyncTask code？
私有类MyAsyncTask扩展的AsyncTask＆LT;字符串，整数，太虚＆GT; { 私人的ArrayList＆LT;地图＆LT;字符串，字符串＆GT;＆GT;清单;
私人进度进度;
@覆盖
保护无效doInBackground（字符串...为arg0）{ 进度=（进度）findViewById（R.id.year_expense_progressbar）;
progressBar.setVisibility（View.VISIBLE）;
。getListView（）setVisibility（View.GONE）;
textView.setVisibility（View.GONE）; 名单=新的ArrayList＆LT;地图＆LT;字符串，字符串＆GT;＆GT;（）; 字符串时间=;
串类=;
字符串费用=;
字符串日=;
串月=;
totalExpense = 0;
光标C = SQLLiteAdapter.fetchAllItems（）; 而（c.moveToNext（）！= FALSE）{ 如果（isCancelled（））{
Log.e（取消，取消里面的背景）;
打破;
}
//如果不输入，不执行verifyLevel
如果（tokenizedResult.isEmpty（））破;
类别= c.getString（c.getColumnIndex（SQLLiteAdapter.col_category））;
费用= c.getString（c.getColumnIndex（SQLLiteAdapter.col_price））;
时间= c.getString（c.getColumnIndex（SQLLiteAdapter.col_time））;
天= c.getString（c.getColumnIndex（SQLLiteAdapter.col_day））;
一个月= c.getString（c.getColumnIndex（SQLLiteAdapter.col_month））;
VerifyLevel一个=新VerifyLevel（tokenizedResult，类别，费用，时间，日，月）;
如果（！a.isEmpty（））{
list.add（a.addToList（））;
} totalExpense + = a.totalExpense;
} 返回null;
} @覆盖
保护无效onPostExecute（虚空结果）
{
progressBar.setVisibility（View.GONE）;
。getListView（）setVisibility（View.VISIBLE）;
textView.setVisibility（View.VISIBLE）;
fillData（名单）;
textView.setText（总费用是+ convertNumeric（totalExpense））;
Log.i（yearExpense，buildList完成）; } @覆盖
保护无效onCancelled（）{
super.onCancelled（）;
list.clear（）;
progressBar.setVisibility（View.GONE）;
totalExpense = 0;
Log.i（yearEx，取消的AsyncTask）;
Toast.makeText（getApplicationContext（），取消，Toast.LENGTH_SHORT）.show（）; }
}
我的做法略有不同，也许，有点冗长。但它一直工作没有任何问题。
这件code的云在 doInBackground（）。如果你有一个的......在这循环，然后使用打破; 语句。如果不使用的....循环，将其删除。
//检查用户是否有已取消任务
如果（isCancelled（））{
cancelTask = TRUE; //（可选）这是额外的检查，我都习惯了。 IT作为故障安全思考。
打破; //移除如果不使用在for循环
}
您已经有一个的AsyncTask 声明： MyAsyncTask的AsyncTask =新MyAsyncTask（）; 。伴随着的是，还可以创建布尔的两个实例。打电话给他们，例如：
布尔blMyAsyncTask;
布尔cancelTask;
现在，在上preExecute（），切换blMyAsyncTask实例的状态：
blMyAsyncTask = TRUE;
而在 onPostExecute（）：
blMyAsyncTask = FALSE;
和，在相同的 onPostExecute（），我也做了其余功能检查 cancelTask布尔的状态之后，。例如：
如果（cancelTask == FALSE）{
// THE师范大学code你有你的onPostExecute（）
}
最后，在的onDestroy（）（我用这个，但我怀疑的onPause（）可以工作也千万不要在的onPause（）在所有诚实），检查的状态布尔blMyAsyncTask
如果（blMyAsyncTask ==真）{
asyncTask.cancel（真）;
}
正如我在开始时说，这是漫长的，甚至可能是复杂的，但它从来没有失败过。我也认为这是一个小的模块的，如果你会的。如果我有更多的 Asycntasks 添加到的活动，我可以在的onDestroy添加其他检查（）。
I am learning how to cancel asyncTask so there is no uses on the code below.
I tried to called the asyncTask and execute it then cancel it and execute it.
MyAsyncTask asyncTask = new MyAsyncTask();
Log.i("cancel","cancel 1");
asyncTask.execute();
Log.i("cancel","cancel 2");
asyncTask.onCancelled();
Log.i("cancel","cancel 3");
asyncTask.execute();
Log.i("cancel","cancel done");
"cancel 1" and "cancel 2" is executed finely as it shown on logcat but ActivityThread.performLaunchActivity error is thrown when "cancel 3" is trying to execute. (cancel 3 is not showing on logcat) Anything wrong with my asyncTask code?
private class MyAsyncTask extends AsyncTask<String,Integer,Void>{
private ArrayList<Map<String, String>> list;
private ProgressBar progressBar;
@Override
protected Void doInBackground(String... arg0) {
progressBar = (ProgressBar)findViewById(R.id.year_expense_progressbar);
progressBar.setVisibility(View.VISIBLE);
getListView().setVisibility(View.GONE);
textView.setVisibility(View.GONE);
list = new ArrayList<Map<String, String>>();
String time = "";
String category = "";
String expense = "";
String day = "";
String month = "";
totalExpense = 0;
Cursor c = SQLLiteAdapter.fetchAllItems();
while(c.moveToNext() != false){
if(isCancelled()){
Log.e("cancel","cancel inside background");
break;
}
// if there is nothing is input, don't execute verifyLevel
if(tokenizedResult.isEmpty()) break;
category = c.getString(c.getColumnIndex(SQLLiteAdapter.col_category));
expense = c.getString(c.getColumnIndex(SQLLiteAdapter.col_price));
time = c.getString(c.getColumnIndex(SQLLiteAdapter.col_time));
day = c.getString(c.getColumnIndex(SQLLiteAdapter.col_day));
month = c.getString(c.getColumnIndex(SQLLiteAdapter.col_month));
VerifyLevel a = new VerifyLevel(tokenizedResult,category,expense,time,day,month);
if(!a.isEmpty()){
list.add(a.addToList());
}
totalExpense += a.totalExpense;
}
return null;
}
@Override
protected void onPostExecute(Void result)
{
progressBar.setVisibility(View.GONE);
getListView().setVisibility(View.VISIBLE);
textView.setVisibility(View.VISIBLE);
fillData(list);
textView.setText("Total Expense is "+convertNumeric(totalExpense));
Log.i("yearExpense","buildList is finished");
}
@Override
protected void onCancelled(){
super.onCancelled();
list.clear();
progressBar.setVisibility(View.GONE);
totalExpense = 0;
Log.i("yearEx","Cancel asyncTask");
Toast.makeText(getApplicationContext(), "cancelled", Toast.LENGTH_SHORT).show();
}
}
My approach is slightly different and perhaps, a little lengthy. But it has always worked without any issues.
This piece of code goes in the doInBackground(). If you have a for... loop in it, then use the break; statement. If you do not use a for.... loop, remove it.
// CHECK IF THE USER HAS CANCELLED THE TASK
if (isCancelled()) {
cancelTask = true; // (OPTIONAL) THIS IS AN ADDITIONAL CHECK I HAVE USED. THINK OF IT AS A FAIL SAFE.
break; // REMOVE IF NOT USED IN A FOR LOOP
}
You already have an Asynctask declared: MyAsyncTask asyncTask = new MyAsyncTask();. Along with that, also create two instances of boolean. Call them, for example:
boolean blMyAsyncTask;
boolean cancelTask;
Now, in the onPreExecute(), toggle the status of the blMyAsyncTask instance:
blMyAsyncTask = true;
And in the onPostExecute():
blMyAsyncTask = false;
And, in the same onPostExecute(), I also do the remainder functions after checking the state of the cancelTask boolean. For example:
if (cancelTask == false) {
// THE NORMAL CODE YOU HAVE IN YOUR onPostExecute()
}
Finally, in the onDestroy() (I use this, but I suspect the onPause() could work too. Never done it in the onPause() in all honesty), check the status of the boolean blMyAsyncTask
if (blMyAsyncTask== true) {
asyncTask.cancel(true);
}
As I said at the start, it is lengthy, perhaps even complicated, but it has never failed. I also think of this as a little modular if you would. If I have more Asycntasks added to the Activity, I can add another check in the onDestroy().
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