java - What is an AsyncTask (or AsyncResult) and how is it typically used for Android? -

can't find concept. have referred to

https://android.googlesource.com/platform/frameworks/base/+/master/core/java/android/os/asyncresult.java

https://docs.oracle.com/javaee/6/api/javax/ejb/asyncresult.html

edit: believe asyncresult referring particular name chosen hold result generic asynchronous operation. (background operation asynchronously notify user when done.)

it seems links above particular implementations of concept.
reference, see these instead:

• developer.android.com - asynctask

• developer.android.com - processes , threads

theory

it important avoid blocking main (ui) thread tasks such downloading content web. i.e. user should able interact app. in situations these need use asynctask.

implementation

the asynctask generic class. first argument parameter of important method doinbackground(). if nothing else, need implement method 1 doing of work.

when doinbackground() finishes, onpostexecute() method called. argument of method same third parameter of asyntask generic class.

example

again using example of blocking task being download web, following example downloads image , displays in imageview. doinbackground() method downloads image , stores in object of type bitmap. onpostexecute() method takes bitmap , places in imageview.

class downloadimagetask extends asynctask<string, void, bitmap> {     imageview bitimage;      public downloadimagetask(imageview bitimage) {         this.bitimage = bitimage;     }      protected bitmap doinbackground(string... urls) {         string urldisplay = urls[0];         bitmap mbmp = null;         try {             inputstream in = new java.net.url(urldisplay).openstream();             mbmp = bitmapfactory.decodestream(in);         } catch (exception e) {             log.e("error", e.getmessage());             e.printstacktrace();         }         return mbmp;     }      protected void onpostexecute(bitmap result) {         bitimage.setimagebitmap(result);     } }