Android async task
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This document discusses Android AsyncTask, which allows performing long/background operations without threads. It has four main methods: doInBackground runs the long operation, onPostExecute displays results after completion, onPreExecute runs before doInBackground, and onProgressUpdate reports progress. An example AsyncTask downloads files, tracking progress in onProgressUpdate and displaying results in onPostExecute after doInBackground finishes downloading. AsyncTask requires specifying types for parameters, progress, and results.
![AsyncTask Example
private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> {
protected Long doInBackground(URL... urls) {
int count = urls.length;
long totalSize = 0;
for (int i = 0; i < count; i++) {
totalSize += Downloader.downloadFile(urls[i]);
publishProgress((int) ((i / (float) count) * 100));
// Escape early if cancel() is called
if (isCancelled()) break;
}
return totalSize;
}
protected void onProgressUpdate(Integer... progress) {
setProgressPercent(progress[0]);
}
protected void onPostExecute(Long result) {
showDialog("Downloaded " + result + " bytes");
}
}](https://image.slidesharecdn.com/androidasynctask-140330083608-phpapp02/85/Android-async-task-4-320.jpg)
Android async task
- 2. Introduction to AsycnTask AsyncTask is an abstract class provided by Android which helps us to use the UI thread properly. This class allows us to perform long/background operations and show its result on the UI thread without having to manipulate threads.
- 3. AsyncTask Methods • doInBackground: Code performing long running operation goes in this method. When onClick method is executed on click of button, it calls execute method which accepts parameters and automatically calls doInBackground method with the parameters passed. • onPostExecute: This method is called after doInBackground method completes processing. Result from doInBackground is passed to this method. • onPreExecute: This method is called before doInBackground method is called. • onProgressUpdate: This method is invoked by calling publishProgress anytime from doInBackground call this method.
- 4. AsyncTask Example private class DownloadFilesTask extends AsyncTask<URL, Integer, Long> { protected Long doInBackground(URL... urls) { int count = urls.length; long totalSize = 0; for (int i = 0; i < count; i++) { totalSize += Downloader.downloadFile(urls[i]); publishProgress((int) ((i / (float) count) * 100)); // Escape early if cancel() is called if (isCancelled()) break; } return totalSize; } protected void onProgressUpdate(Integer... progress) { setProgressPercent(progress[0]); } protected void onPostExecute(Long result) { showDialog("Downloaded " + result + " bytes"); } }
- 5. AsyncTask Execute 3 Parameters for the Asynctask • Params – parameters sent to the task upon execution • Progress – progress units published during background execution • Result – result of the task after completion private class MyTask extends AsyncTask<Void, Void, Void> { ... } Unused parameters can be set as void New DownloadfilesTasks().execute (URL, null, null);