AsyncTask中cancel方法的作用是什么

本篇文章為大家展示了AsyncTask中cancel方法的作用是什么，內容簡明扼要并且容易理解，絕對能使你眼前一亮，通過這篇文章的詳細介紹希望你能有所收獲。

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Cancelling  a task

A task can be cancelled at any time by invoking cancel(boolean).  Invoking this method will cause subsequent calls to isCancelled() to return  true. After invoking this method, onCancelled(Object), instead of  onPostExecute(Object) will be invoked after doInBackground(Object[]) returns. To  ensure that a task is cancelled as quickly as possible, you should always check  the return value of isCancelled() periodically from doInBackground(Object[]), if  possible (inside a loop for instance.)

這是話意思是

我們可以隨時調用 cancel（boolean）去取消這個加載任務，調用這個方法會間接調用 iscancelled 并且返回true  。

當調用cancel()后，在doInBackground（）return后 我們將會調用onCancelled(Object)  不在調用onPostExecute(Object)

為了保證任務更快取消掉，你應該在doInBackground（）周期性的檢查iscancelled  去進行判斷。

**注意，我們的oncancel和onPostExecute一樣，都是在UI線程中執行。。。所以當我們想要取消之后，有些界面變化  我們可以在oncancel里面改變UI.

關于cancel方法

public final boolean cancel (boolean  mayInterruptIfRunning)

Attempts to cancel execution of this task. This  attempt will fail if the task has already completed, already been cancelled, or  could not be cancelled for some other reason. If successful, and this task has  not started when cancel is called, this task should never run. If the task has  already started, then the mayInterruptIfRunning parameter determines whether the  thread executing this task should be interrupted in an attempt to stop the  task.

某些情況下，我們調用cancel（true）可能就會失效

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