Update custom View at run-time in background thread

Last example demonstrate "drawing on custom View" in onCreate() before the view displayed. It's modified to update the display item in background thread at run-time.

The update job is perform in AsyncTask. To request onDraw() of View to be called, your code have to invalidate the view. invalidate() method must be called from a UI thread. To call from a non-UI thread, call postInvalidate().

Modify MainActivity.java from the last exercise.

package com.example.androidgraphview;

import java.util.Random;

import android.os.AsyncTask;
import android.os.Bundle;
import android.os.SystemClock;
import android.app.Activity;

public class MainActivity extends Activity {
 
 MyGraphView myGraphView;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  myGraphView = (MyGraphView)findViewById(R.id.myview);
  
  new MyAsyncTask(myGraphView).execute();

 }
 
 public class MyAsyncTask extends AsyncTask<Void, Void, Void> {

  MyGraphView myTaskView;
  
  MyAsyncTask(MyGraphView v){
   myTaskView = v;
  }
  
  @Override
  protected Void doInBackground(Void... arg0) {
   Random random = new Random();

   for(int i = 0; i <= 500; i++){
    myTaskView.addItem(i, random.nextInt(500));
    myTaskView.postInvalidate();
    SystemClock.sleep(100);
   }
   
   return null;
  }
  
 }

}

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