Asynctask is used in Android to download files and dynamically update the progress bar

1. Generics

AysncTask<Params,Progress,Result>

Params: the parameter passed in when starting the task, which is passed in by calling the asynctask. Execute (param) method.

Progress: the progress of background task execution. If the progress bar is not displayed, it does not need to be specified.

Result: the result returned at the end of the background task.

2. Important methods

Doinbackground (params... Params): the method that must be overridden. The background task is executed here and a new thread will be started. Params is the parameter passed in when starting the task. The number of parameters is variable.

OnPreExecute (): in the main thread, the operation before the background task is opened, such as displaying a progress bar dialog box.

OnPostExecute (Result result): when the background task is finished, it is called in the main thread to process the results returned by the doInBackground () method.

OnProgressUpdate (Progress... Values): when publishProgress (Progress... Values) is invoked in doInBackground (), it is called back to the main thread, and the number of parameters here is also uncertain.

Oncancelled(): cancels the task.

3. Precautions

(1) the execute () method must be invoked in the main thread.

(2) Asynctask instance must be created in the main thread;

(3) Do not manually call doinbackground(), onpreexecute(), onpostexecute(), onprogressupdate() methods;

(4) Pay attention to prevent memory leakage. Strong reference to activity in doinbackground () method may cause memory leakage.

4. Download File dynamic update progress bar (not encapsulated)

Layout:

Activity：

5. Download files and dynamically update the progress bar (encapsulation)

Activity：

DownloadHelper：

summary

The above is what Xiaobian introduced to you. In Android, asynctask is used to download files and dynamically update the progress bar. I hope it will be helpful to you. If you have any questions, please leave me a message and Xiaobian will reply to you in time. Thank you very much for your support for the programming tips website!