Implementing Activity Callback Methods

Android Tutorials - Herong's Tutorial Examples

∟android.app.Activity Class and Activity Lifecycle

∟Implementing Activity Callback Methods

This section provides a tutorial example on how to implement activity callback methods using ActivityLog application as an example to log a short message from each callback method in a log file.

In this tutorial, I am going to enhance my ActivityLog application to implement other callback methods. See the ActivityLog.java source code below:

/* ActivityLog.java
 * Version 2.0 - Adding more callback methods
 * Copyright (c) 2015, HerongYang.com, All Rights Reserved.
 */
package com.herongyang.activity;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
import android.content.Context;
import java.io.*;
public class ActivityLog extends Activity {
   @Override
   public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      String msg = "";
      msg += "Activity created\n";
      msg += "----------------\n";
      TextView tv = new TextView(this);
      tv.setText(msg);
      setContentView(tv);

      logLine("Checkpoint #1 - onCreate() called");
   }
   public void onStart() { //working
      super.onStart();
      logLine("Checkpoint #2 - onStart() called");
   }
   public void onResume() {
      super.onResume();
      logLine("Checkpoint #3 - onResume() called");
   }
   public void onPause() {
      super.onPause();
      logLine("Checkpoint #4 - onPause() called");
   }
   public void onStop() {
      super.onStop();
      logLine("Checkpoint #5 - onStop() called");
   }
   public void onRestart() {
      super.onRestart();
      logLine("Checkpoint #6a - onRestart() called");
   }
   public void onDestroy() {
      super.onDestroy();
      logLine("Checkpoint #6b - onDestroyed() called");
   }
   public void logLine(String msg) {
      try {
         FileOutputStream fos =
            openFileOutput("Activity.log", Context.MODE_APPEND);
         OutputStreamWriter out = new OutputStreamWriter(fos);
         out.write((new java.util.Date()).toString()+": "+msg+"\n");
         out.close();
         fos.close();
      } catch (Exception e) {
         e.printStackTrace(System.err);
      }
   }
}

Some notes on the enhanced ActivityLog.java code:

When implementing your own callback methods, onStart(), onResume(), onPause(), onStop(), onRestart() and onDestroy(), you have to call the super class's implementation of the same method. Otherwise, an execution exception will be thrown.
A checkpoint number is used in the log to help showing the sequence of when each callback method is called.

Now build and install the enhanced version of ActivityLog to the emulator. Then follow next tutorials on how to test the activity lifecycle by running ActivityLog in different ways.