This post show some examples to Get and Set UI elements from AsyncTask. the "Start AsyncTask" button clicked, it new and execute a AsyncTask, to get and set UI elements in various call-back method, in UI thread and background thread.
- Starting with HONEYCOMB, AsyncTask are executed on a single thread to avoid common application errors caused by parallel execution - read Run multi AsyncTask at the same time.
So call myClientTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR) if it is running on device higher than HONEYCOMB. - For the ProgressBar, it's a simple and standard demo: update counter in doInBackground(), and call publishProgress() to call onProgressUpdate() in-directly to update the ProgressBar in UI thread.
- In onPreExecute() and onPostExecute(), it run on UI thread, so you can access UI elements directly.
- In doInBackground(), it run on background thread; to read data from EditText textIn2 and update TextView textOut2.
- In background thread, it can read UI elements, so it can call textIn2.getText() directly. (If I am wrong, please comment)
- In background thread, it CANNOT modify UI element, call runOnUiThread() and pass a Runnable to update textOut2 in UI thread.
MainActivity.java
package com.example.androiduiasynctask;
import android.support.v7.app.ActionBarActivity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.annotation.TargetApi;
import android.os.AsyncTask;
import android.os.Build;
import android.os.Bundle;
import android.os.SystemClock;
public class MainActivity extends ActionBarActivity {
EditText textIn1, textIn2;
TextView textCounter;
Button btnStart, btnClear;
ProgressBar progressBar;
TextView textOut1, textOut2, textOut3;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textIn1 = (EditText)findViewById(R.id.textin1);
textIn2 = (EditText)findViewById(R.id.textin2);
textCounter = (TextView)findViewById(R.id.counter);
btnStart = (Button)findViewById(R.id.start);
btnClear = (Button)findViewById(R.id.clear);
progressBar = (ProgressBar)findViewById(R.id.progress);
textOut1 = (TextView)findViewById(R.id.textout1);
textOut2 = (TextView)findViewById(R.id.textout2);
textOut3 = (TextView)findViewById(R.id.textout3);
btnStart.setOnClickListener(MyOnClickListener);
btnClear.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View arg0) {
progressBar.setProgress(0);
textOut1.setText("");
textOut2.setText("");
textOut3.setText("");
}});
}
OnClickListener MyOnClickListener = new OnClickListener(){
@TargetApi(Build.VERSION_CODES.HONEYCOMB) @Override
public void onClick(View v) {
MyAsyncTask myAsyncTask = new MyAsyncTask();
/*
* Handle multi AsyncTask at the same time
* Refer: http://android-er.blogspot.com/2014/04/run-multi-asynctask-as-same-time.html
*/
if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB)
myAsyncTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
else
myAsyncTask.execute();
}
};
public class MyAsyncTask extends AsyncTask<Void, Integer, Void>{
@Override
protected void onPreExecute() {
//In UI thread, you can access UI here
super.onPreExecute();
String s1 = textIn1.getText().toString();
textOut1.setText(s1);
}
@Override
protected Void doInBackground(Void... arg0) {
for(int i=0; i<=10; i++){
SystemClock.sleep(1000);
publishProgress(i); //update UI in onProgressUpdate
//Can GET from UI elements
String s2 = textIn2.getText().toString();
final String msgInBackGround = "doInBackground: " + i + " - " + s2;
/*
* Cannot direct SET UI elements in background thread
* so do with runOnUiThread()
*/
runOnUiThread(new Runnable(){
@Override
public void run() {
textOut2.setText(msgInBackGround);
}});
}
return null;
}
@Override
protected void onPostExecute(Void result) {
//In UI thread, you can access UI here
textOut3.setText("onPostExecute");
super.onPostExecute(result);
}
@Override
protected void onProgressUpdate(Integer... values) {
//In UI thread, you can access UI here
progressBar.setProgress(values[0]);
super.onProgressUpdate(values);
}
}
}
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:orientation="vertical"
tools:context="com.example.androiduiasynctask.MainActivity" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:autoLink="web"
android:text="http://android-er.blogspot.com/"
android:textStyle="bold" />
<EditText
android:id="@+id/textin1"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
<EditText
android:id="@+id/textin2"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
<TextView
android:id="@+id/counter"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
<Button
android:id="@+id/start"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Start AsyncTask"/>
<Button
android:id="@+id/clear"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Clear"/>
<ProgressBar
android:id="@+id/progress"
style="?android:attr/progressBarStyleHorizontal"
android:indeterminate="false"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:max="10"
android:progress="0"/>
<TextView
android:id="@+id/textout1"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
<TextView
android:id="@+id/textout2"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
<TextView
android:id="@+id/textout3"
android:layout_width="match_parent"
android:layout_height="wrap_content"/>
</LinearLayout>
