ActivityLog - Application to Create Log File

Android Tutorials - Herong's Tutorial Examples

∟android.app.Activity Class and Activity Lifecycle

∟ActivityLog - Application to Create Log File

This section provides a tutorial example on how to create application, ActivityLog, to create a log file to monitor activity lifecycle using the android.content.Context.openFileOutput() method.

The best way to monitor the lifecycle of an activity is to write messages into a log file. For that, we need to learn how to open a file and write text messages to the file on an Android system.

According to the Android reference document, the android.content.Context class provides you methods to interface with the data folder assigned to your application in the file system.

abstract FileOutputStream openFileOutput(String name, int mode) - Open a private file associated with this Context's application package for writing.
abstract FileInputStream openFileInput(String name) - Open a private file associated with this Context's application package for reading.

Now I am ready to create a new application, ActivityLog, with a new package, com.herongyang.activity:

C:\>cd \herong
C:\herong>set JAVA_HOME=\Program Files\Java\jdk1.8.0_45\

C:\herong>\local\android-sdk-windows\tools\android create project \
   --package com.herongyang.activity --activity ActivityLog --target 2 \
   --path .\ActivityLog
Created project directory: C:\herong\ActivityLog
..
Added file C:\herong\ActivityLog\build.xml

C:\herong>cd ActivityLog
C:\herong\ActivityLog>del .\res\layout\main.xml

Modify the Activity Java class, .\src\com\herongyang\activity\ActivityLog.java, to write a short message to a log file:

/* ActivityLog.java
 * Version 1.0 - Creating the log file
 * 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";

      try {
         FileOutputStream fos =
            openFileOutput("Activity.log", Context.MODE_APPEND);
         OutputStreamWriter out = new OutputStreamWriter(fos);
         out.write(msg);
         out.close();
         fos.close();
      } catch (Exception e) {
         e.printStackTrace(System.err);
      }

      TextView tv = new TextView(this);
      tv.setText(msg);
      setContentView(tv);
   }
}

Note that:

I removed the .\res\layout\main.xml file, because I am creating my own TextView object and using the default layout to manage the view in my activity Java code.
I am using Context.MODE_APPEND when opening the log file so that new log messages will be appended to the end of the log file.