Develop Reference

How to determine the source of a log in LogCat?

Is it possible to determine the location in code, where a particular message was written to LogCat?
I would like to have something like a stack trace for each log, since some logs are of unknown source.

Why don't you use Android Debug or simply try to show Log.v("Your messsage"+your response) where ever needed. So that you can get idea where your application reached at that particular time when that Log prints on your LogCat

Android Studio Log Cat continuously Shows data

I have searched this issue in SO, but those answers did not help me.
I have recently updated my Android SDK in Android Studio. After that whenever I connect my device via USB, it shows whole data from Android Device in the Logcat. I thought of filtering it by selecting Debug, Verbose and error according to the usage. But still there is unnecessary data in everything. In previous SDK, I did not see this problem. How to solve avoid unnecessary data?

The show only selected application filter only works if you have an application selected. In the toolbar above it no debuggable applications indicates it did not find any application to filter so it simply shows the entire logcat output.
Build and deploy an application to the device and then select the application from the dropdown many that now says no debuggable applications. The output should then be filtered to only your application.

Choose the Log level to waring or error, and in your code use
log.w("TAG", "Warning log message");
or
log.e("TAG", "Error log message");
If you want to use the debug log level, you can use
log.d("MYDEBUGTAG", "Debugg log message");
and filter the debugging messages by typing your tag "MYDEBUGTAG" on the textbox next to the log level selector.
Hope it helps.

Code to Get Data from type error in logcat programmatically

I have gone through many tutorials, but I haven't found how to get the error logs.
I found one link:
http://www.helloandroid.com/tutorials/reading-logs-programatically
and gone through it. I want only error logs, I don't know which command must write to show error logs. My requirement is to send the logs through email, I don't want any adb command. I want the command to write in java to read the logs of error/debug/info.
Example: to dump a file, they have written code like
Process process = Runtime.getRuntime().exec("logcat -d");
To print only error logs, what command should I write?
Gone through Andorid Developers Blog: http://developer.android.com/tools/debugging/debugging-log.html

Process process = Runtime.getRuntime().exec("logcat -d *:E");

If you want an error log, just write: Log.e("MyClass", "This is an error");
And if you want to display errors only, just change the log level in Android Studio like this:

Capture Complete LOGS In Android

I was wondering how do i take complete logs from android device (From the point of My application initialize to any crash or till force close of my application).
Reason i am posting here is my application is crashed some point,but when i take logs using DDMS/Logcat my crash details are over written with new logs.
How do i get my crashed reason logs..
Specially looking to capture Native Code Crash.
i.e I/DEBUG (21835): signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 00000004...
Will this adb logcat > crash.txt ensures me that write to file will happen forever?

I tried this Works Real Well,Not sure How much battery it will consume..If your Application is in Testing Stage You can use this..Before Release you got to Remove this code and Publish..
private void writeADBLogs(){
BufferedWriter bufferedWriter = null;
try {
final File file = new File(sdcardPath);
bufferedWriter = new BufferedWriter(new FileWriter(file,true));
Process process = Runtime.getRuntime().exec("logcat -d");
BufferedReader bufferedReader = new BufferedReader( new InputStreamReader(process.getInputStream()));
String oneLine;
while ((oneLine= bufferedReader.readLine()) != null) {
bufferedWriter.write(oneLine);
bufferedWriter.newLine();
}
} catch (IOException e) {
e.printStackTrace();
}
}

The Android Log will be save only when Your application has Debugging = true in manifest (i.e when you are in Debug mode).
See Documentation at Turn off logging and debugging
So in that case if you want the log then you can implement Thread.setDefaultUncaughtExceptionHandler (Thread.UncaughtExceptionHandler handler)
This will be called always when your application is force closed due to Exception.
What you do is save the StackTrace in a file in append mode.
You can also use this in Debug Mode.
LogCat is a Queue so there are changes that you will miss your log (old Log will be automatically discarded).
I suggest you to implement setDefaultUncaughtExceptionHandler so you never miss any exception log. Also take care to delete the file after use or else your file will became very big in size by time.

install aLogCat app, then if your app crashes, launch it. Use filter (from menu) to narrow data to related to your application and eventually save it or send from device via mail to you. But it won't do much magic - if logs are phisically gone from device it won't send you more you can have with DDMS. It's however quite useful if your users report crashes.

Assuming you have access to the device:
Hook the device up to the computer.
Run DDMS, select the device, and go to the file explorer tab.
Find the file referenced in LogCat, and click on the Pull from Device button near the top.

You should use unique Logtags for your messages so you can Filter the cat for that. E.g. getPackageName() is a nice candidate and it's returning a string.
In Eclipse you can click on the green + to add another filer for LogCats View. In the window you repeat your tag in the field "by log tag".
Also it seems there's automatically a new Tab called "session filter" when I start my app from Eclipse - providing relevant Logs including but not only the ones written by the programmer.
You can also grab the log directly from the console using Android Developer Bridge. adb logcat is the command you're looking for and according to man there are also the same filter settings applicable. Though I couldn't figure out the syntax :)

You can use acra with your application.It helps you to get the crash reports in your gdoc account you can also configure it to get an email for crash report.Once your app goes live then it also helps you to get the crash report.
http://code.google.com/p/acra/

How to output messages to the Eclipse console when developing for Android

How can I print messages (like a flag) to the Eclipse console (or log) when developing and debugging an Android app

Rather than trying to output to the console, Log will output to LogCat which you can find in Eclipse by going to: Window->Show View->Other…->Android->LogCat
Have a look at the reference for Log.
The benefits of using LogCat are that you can print different colours depending on your log type, e.g.: Log.d prints blue, Log.e prints orange. Also you can filter by log tag, log message, process id and/or by application name. This is really useful when you just want to see your app's logs and keep the other system stuff separate.

Log.v("blah", "blah blah");
You need to add the android Log view in eclipse to see them. There are also other methods depending on the severity of the message (error, verbose, warning, etc..).

System.out.println() also outputs to LogCat. The benefit of using good old System.out.println() is that you can print an object like System.out.println(object) to the console if you need to check if a variable is initialized or not.
Log.d, Log.v, Log.w etc methods only allow you to print strings to the console and not objects. To circumvent this (if you desire), you must use String.format.

I use Log.d method also please import import android.util.Log;
Log.d("TAG", "Message");
But please keep in mind that, when you want to see the debug messages then don't use Run As
rather use "Debug As" then select Android Application. Otherwise you'll not see the debug messages.

i use below log format for print my content in logCat
Log.e("Msg","What you have to print");