තාලකගේ සටහන් (Thaalakaz): August 2015

Android activity life cycle and android studio debugging using logact.

Hi friends, today we are going to learn how to use logcat for debugging your code in android studio. For the demonstration I’ll use android activity life cycle J.If you are new to android there may be numerous questions in your mind about android activity lifecycle.

What is the lifecycle of android activity?

Why are those similar sounding methods (onCreate(), onStart(), onResume()) called during initialization,& others (onPause(), onStop(), onDestroy()) called at the end?

Normally android activity have 6 status

1. Created

2. Started

3. Resumed

4. Paused

5. Stopped

6. Destroyed

And android activity life cycle has 7 methods.Let’s get an idea about each of these methods from http://developer.android.com/

Method	Description
onCreate()	Called when the activity is first created. This is where you should do all of your normal static set up: create views, bind data to lists, etc. This method also provides you with a Bundle containing the activity's previously frozen state, if there was one.Always followed by onStart()
onRestart()	Called after your activity has been stopped, prior to it being started again.Always followed by onStart()
onStart()	Called when the activity is becoming visible to the user.Followed by onResume() if the activity comes to the foreground, or onStop() if it becomes hidden.
onResume()	Called when the activity will start interacting with the user. At this point your activity is at the top of the activity stack, with user input going to it. Always followed by onPause().
onPause ()	Called as part of the activity lifecycle when an activity is going into the background, but has not (yet) been killed. The counterpart to onResume(). When activity B is launched in front of activity A, this callback will be invoked on A. B will not be created until A's onPause() returns, so be sure to not do anything lengthy here.
onStop()	Called when you are no longer visible to the user. You will next receive either onRestart(), onDestroy(), or nothing, depending on later user activity. Note that this method may never be called, in low memory situations where the system does not have enough memory to keep your activity's process running after its onPause() method is called.
onDestroy()	The final call you receive before your activity is destroyed. This can happen either because the activity is finishing (someone called finish () on it, or because the system is temporarily destroying this instance of the activity to save space. You can distinguish between these two scenarios with the isFinishing() method.

Ø When the Activity first time loads the events are called as below:

onCreate()àonStart()àonResume()

Ø When you click on Phone button the Activity goes to the background and the below events are called:

onPause()àonStop()

Ø Exit the phone dialer and the below events will be called:

onRestart()àonStart()àonResume()

Ø When you click the back button OR try to finish() the activity the events are called as below:

onPause()àonStop()àonDestroy()

Now we are going to look at our hello world application which we gonna use for demonstrating above situations.Edit your MainActivity.java file as below.

MainActivity.java

You may wonder why I am using Log.d (“some text1”,”sometext2”) allover my code. The Android logging system provides a mechanism for collecting and viewing system debug output. Logcat dumps a log of system messages, which include things such as stack traces when the emulator throws an error and messages that you have written from your application by using the Log class.

I am using Log.d() to display my message.As you can see log class contains two parameters called tag & msg .Here I am using “Nadeeshaz” as the tag name for filtering purpose.for the msg I have used the relevant message for each section.

By pressing alt + 6 you will get the logcat window .It shows the logs for selected application. But there it’s really hard to find the log with our tag name.

Go to the drop down list(highlighted) in your right-hand side & select “Edit filter configuration”.

When you click on it you will get the below window.

You have to fill Log Tag with you tag name in my case its “Nadeeshaz” and then you have to give a meaningful name for Filter Name .For more conventions I will use the same name for the filter name.