In the Android Open Source Project's code style, it states that we shouldn't use System.out.println() but I don't understand why. Can anyone explain? What should I use to trace my app's log?
Here's the line for reference:
System.out.println() (or printf() for native code) should never be used. System.out and System.err get redirected to /dev/null, so your print statements will have no visible effects. However, all the string building that happens for these calls still gets executed.
You should use the android.util.Log class.
Here's a description of what the Log class does:
API for sending log output.
Generally, you should use the Log.v(), Log.d(), Log.i(), Log.w(), and Log.e() methods to write logs. You can then view the logs in logcat.
The order in terms of verbosity, from least to most is ERROR, WARN, INFO, DEBUG, VERBOSE. Verbose should never be compiled into an application except during development. Debug logs are compiled in but stripped at runtime. Error, warning and info logs are always kept.
These are the available methods of the Log class:
Log.d() - Send a DEBUG log message.
Log.e() - Send an ERROR log message.
Log.i() - Send an INFO log message.
Log.v() - Send a VERBOSE log message.
Log.w() - Send a WARN log message.
Log.wtf() - What a Terrible Failure: Report an exception that should never happen.
The methods above (with the exception of Log.w and Log.wtf which have 3 possible patterns of arguments) require the following arguments:
String tag, String msg:
tag: Used to identify the source of a log message. This value may be null.
msg: The message you would like logged. This value may be null.
String tag, String msg, Throwable tr - Similar to the first pattern, but allows for an exception to be specified. This pattern should be used if you want to log an exception to the log output.
(For Log.w and Log.wtf) String tag, Throwable tr Similar to the third pattern, but does not allow for a message to be specified. Note that you can still pass a message but it should be in the second arrangement of arguments.
EDIT: Going straight to answer your question: println() of System.out and System.err will still be displayed in logcat but with limitations.
You can't log VERBOSE, ERROR, or DEBUG using System.out or System.err.
You can't define your own tag, it will display System.err or System.out with your text. For instance:
System.out.println("Hello!") is equivalent to Log.i("System.out","Hello!")
System.err.println("Hello!") is equivalent to Log.w("System.err","Hello!")
System.out.println("") in android will not run well because there is no Terminal that the app is corrected to.
You would be better off using Log.(d)(v)(e)(i)(w), because there is something actively monitoring LogCat.
System.out.println() will print to LogCat, but only after an additional set of System instuctions, making it not as efficient, however, as i said, it still works.
if we want to trace the android project
we can do it using Log class
there is some methods like
Log.e(TAG,MESSAGE)
Log.v(TAG,MESSAGE)
Log.w(TAG,MESSAGE)
Log.d(TAG,MESSAGE)
Log.i(TAG,MESSAGE)
its a static method of Utils package. put it line by line and u can watch it in the LogCat..
thats at enjoy with android
From your own link:
System.out.println() (or printf() for native code) should never be
used. System.out and System.err get redirected to /dev/null, so your
print statements will have no visible effects. However, all the string
building that happens for these calls still gets executed.
In addition, at the beginning of that page, it says:
The rules below are not guidelines or recommendations, but strict
rules. Contributions to Android generally will not be accepted if they
do not adhere to these rules.
So DON'T do it!
You can use the built in Log utility that will print right out to the LogCat.
You can use Log.e(String, String) for errors which will appear in red. There is also v, d, i, and w for verbose, debug, info, and warning respectively.
The following should do the trick to print the exception
1. Log.d("myapp", Log.getStackTraceString(new Exception()));
or
2. You can get longer stack traces by digging deeper. For example:
Log.getStackTraceString(e.getCause().getCause());
Log is the best way to trace our android project
like following code...
it will help u...
just look in DDMS logCat that how exactly project is build...
requirement... android.utils.Log; package is used..
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
for(int i=0;i
{
Log.e("i = ",""+i);
Log.v("i = ",""+i);
Log.i("i = ",""+i);
Log.w("i = ",""+i);
Log.d("i = ",""+i);
}
}
i hope it will help u
Related
I am using emojis in log cat messages in order to make the logs easier on the eye. So far it works fine, but I wonder if I'll hit any character compatibility issues on older Android devices. My app's minimumSdkVersion is 16.
Examples:
companion object {
private const val TAG = "\uD83D\uDD36SomeClass"
}
...
Log.d(TAG, "⏰ Something happened!")
Is there anything I should be worried about? Are there any reasons against doing this?
Not sure about your emojis in Logcat but I think that if you want to make your life easier use the TAG that inside your Log.d.
For example, here is a log with a custom TAG:
Log.d("myTag","something to show");
After you run your app all you need to do is to search the same tag name within your logcat, like this:
Another thing that you should think about that if you want to search for a specific log would it be comfortable to search the logcat using emojis?
In my opinion, simply searching your tag name to find your log makes thing super easy.
My package name is getting in the way of me easily reading my logcat messages. I have to scroll way to the right to see anything. Each line is preceded with:
08-07 00:52:58.237 16332-16332/com.mycompay.mypackage.mypackage/System.out:
How can I get rid of the package name there? And what is the 16332-16332 doing there? Can I get rid of that too?
For Custom Logcat You should read Write and View Logs with Logcat
Every Android log message has a tag and a priority associated with it.
The tag of a system log message is a short string indicating the
system component from which the message originates .
The log message FORMAT is:
date time PID-TID/package priority/tag: message
PID stands for process identifier and TID is thread identifier; they
can be the same if there’s only one thread.
People love visual answers, so I'll duplicate the comment here. I believe it will help you understand this faster.
#Mike Miller:
Check out the section titled "Configuring the logcat Header Display." Just click the settings icon on the left side of logcat
For android studio electric eel and above. Use the following icon to edit the logcat - https://i.stack.imgur.com/L6KBg.png
I'm using logcat for monitoring my android projects in a custom way. I export my data,errors,method info and many other options.
I prefer to not to use Log defaults like Lod.d or Log.e or etc.
Is it possible to have my own custome logs for example Log.myLog with a new color in Logcat?
I prefer my logs do not interfere with android logs.
I've searched a lot but can't find anything about this purpose:
http://wiki.cyanogenmod.org/w/Doc:_debugging_with_logcat
http://logc.at/
I can recommend you a good one: https://github.com/oronno/log4android
Features
Log syntax similar with popular log4j framework
Automatically added TAG with log message
Derive TAG from the package name
Can disable logging by simply calling Logger.disableLogging(true) method preferably from the class extends Application.
Fully Qualified Class name or SimpleClassName will logged as prefix with log message
Variable Arguments (more than 2) can be passed for printing unlike log4j framework
Very lightweight, < 5KB library size!
I do use it in my every android application.
some time ago i wrote an eclipse plugin that modifies android.util.Log.* calls so that when
you have in your code:
Log.d(TAG, "********** this is line 49 in onCreate method");
android.util.Log.d(TAG, "********** this is line 50 in onCreate method");
you will see in the LogCat:
D/Test ( 306): onCreate:49, ********** this is line 49 in onCreate method
D/Test ( 306): onCreate:50, ********** this is line 50 in onCreate method
the plugin sources are here: https://github.com/pskink/AndroidLoggerBuilder.git
Maybe you should try to establish its own tag for its log? You can then easily filter logs without having to allocate a different color.
I want to convert a charsequence to String value,I use the following code for that
string passwordTxtValue;
passwordTxtValue = passwordTxt.getText().toString();
System.out.println(""+passwordTxtValue);
But i am not getting the value,how can i resolve this.
In Android System.out.println() gets redirected to LogCat and printed using Log.i(). In java you have System.out.println() instead of that you can use Android Log class in Android for the same purpose. And you can see the output in the Logcat. And one upperhand to see in the Logcat is you can get Stack Traces of any uncaught Exceptions.
Your value get converted correctly, but the java method println() won't work in Android
I am using a system() call in a program , that is in c library. For 1st 9 calls it returns '0'(zero) after 10th call it returns 256. I do not know what does it mean. Please anybody help me. Following is the line of code
int returnValue= system("/system/bin/cat /dev/graphics/fb0 > /tmpdata/Screenshot/screenshot.bin");
According to this man page dealing with the general unix cat command, an error code >0 simply means an error occurred.
The following exit values shall be returned:
0
All input files were output successfully.
>0
An error occurred.
Your system() call is attempting to concatentate two files, so perhaps there is a space issue or maybe the source file does not exist.
You may also wish to take a look at some recent source code for Android cat (cat.c) which gives some indicatations of the kind of things that trigger errors within cat.