I develop android apps.
I'm in some confusion about LogCat.
If I sometimes can't Judge where is the error exactly if my app force closes. Is there any way or shortcuts to know where our error exactly ?
If you are developing the application you should know logcat to know the error. It give the complete trace of error. (Exception name and line no etc.)
Without understanding logcat you can not make application in android.
Second thing: If you have developed application, distributed in market and user have some problem in your app. For get to know logcat or errors you can use.
ACRA
Bugsense
Ive got a strange issue that has me beating my head into a brick wall. In my android app I have a method that checks the mobile state and depending on the outcome pulls an image from on line. I started to receive java.lang.NullPointerException in the developer console. It was being caused by there being no mobile state to check. Simple enough and was fixed with an if statement.
This method was in several activity's and the fix was applied to all. For some reason I am still receiving errors in the console but only for one of the activity's. The error message is the same as last time, and Ive been through the code a million times it shouldn't be doing it has the same fix as the other activity's. Also I cannot re create the error, which is making it impossible to fix. As far as I can see its not broke.
Any suggestions of what to do in this situation? Would a try and catch be appropriate?
Try cleaning (in eclipse, Project -> Clean...) your project. I find this sometimes fixes issues with the app seamingly not being updated when changes are made to the source...whether the source being a resource or source code.
Perhaps check if there are any contexts not clearly defined. Or if you simply wrote one of "(this)", try being more explicit: "(mainactivity.this)"
I have just started doing Android development on Mac OS X in Eclipse. When debugging an Activity, I keep getting the following errors:
The JAR file /platforms/android-10/android.jar has no source attachment.
This is starting to get very annoying, does it mean something is throwing an exception somewhere? (the message itself does not give any meaningful information as to why this is happening) I do not want to step into the source; does Eclipse do this by default? How do I disable it?
It looks like you have some error in your application. And Android subsystem throws exception. Normally, if such exception originates from android, you'll see this behavior.
What you should do:
Turn on LogCat view to see logs.
Launch your app without debugger (Ctrl+F11 on ubuntu/windows)
Inspect those logs in LogCat very carefully. They will contain the place where exception happened (originating from your code). You will then easily be able to fix the issue yourself (or ask for more assistance if needed).
In a normal development workflow you shouldn't hit cases like yours too often. Its just the learning curve :) So stay calm and keep learning.
I'm working on my first Android app and to be honest I'm not sure about most of what I'm doing. Right now I'm stuck on a NullPointerException that is created by a line that refers to another class that, in turn, refers to another class.
How can I locate the error?
The word you are looking for is debug. If you are using eclipse, it's very easy to debug your program in most cases. Two main options in eclipse are to use the logger for debug prints to logcat, or debug the program step by step to detect relevant errors. Here is a tutorial for both options and here is a nice video tutorial in YouTube regarding debug in eclipse.
You can use the Eclipse debugger to help with that. Set a break point above the line that errors out and deploy your app using the Eclipse debugger (with the little bug icon) rather than the standard deployer (the play button). You'll be able to see what is going on right before the line with the error occurs and hopefully fix things up.
If that doesn't work, you can post the stack trace and your method that has the error and we can take a look at it.
Try the following:
Create a HelloWorld application.
Add a Log statement to the end of onCreate:
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Log.d("HelloWorldActivity.onCreate()", "setContentView() completed");
}
Place a breakpoint on the Log statement.
Run the app in the emulator and note it works and step to see the Logged entry in the LogCat window of Eclipse.
Change the HelloWorldActivity to extend from ListActivity instead of Activity.
public class HelloWorldActivity extends ListActivity {
Run the app in the emulator again and note it fails to reach the Log statement.
My question is NOT why this fails. My question is, how would you go about debugging this failure? All I see in the Eclipse Debug pane is a RuntimeException. I see LogCat has a bunch of messages, but it's huge and I've searched it but can't find anything to indicate what's wrong or where in my code the exception happened. I can't find a way to display the message inside the RuntimeException or a stack trace to know which line of code initiated the exception.
I assume there must be better ways to use the tools to find errors, but I'm new and can't seem to figure out a better way to debug besides wrapping everything I code in a try/catch. I would have expected to find a message in LogCat generated by the throwing of the exception. I would have expected the Debug window to allow you to inspect the exception's contents. I'm not saying that such techniques don't exist, I'm saying I'm having trouble figuring out as a beginner how to debug and asking what techniques do exist and how do I use them?
So, simply put:
How would you find this error if you didn't already know what was causing it?
What techniques would you use to find out the root cause?
How would you go about inspecting the Exception's details?
Generally, how do you find problems in your Android code using Eclipse?
Multiple suggestions and discussion are welcomed. :)
I would have included my LogCat contents, but it's so large that's not reasonable. You should be able to easily reproduce this yourself, so I left it out. It is possible something is in LogCat to help me, but because it's so large with even running a small program, I would need a hint as to what to search for and how to interpret it when hitting an exception thrown from an API call. I see other posts that state something should be in LogCat, which while might be true, I'm not finding anything myself. If you think something should be in LogCat, please run the test yourself and copy the lines into your response that I should be finding.
Thanks.
========
Summary techniques list so far is as follows:
Invasive Techniques:
1. Place a Toast in code locations where you want to see you you've executed.
2. Place try/catch around code where you think there's a possibility of an Exception being thrown.
3. Comment out code and recompile and retest.
Non-Invasive Techniques:
1. Use the debugger. Breakpoints, variable inspection...
2. Monkey stress tester.
3. Download Android source library.
4. Use LogCat filters to see if a "Caused By" is listed.
Unclear if Available:
1. Debug version of Android library that has additional logging, assertions or other additional help.
2. Ability to inspect an Exception in Eclipse through the Debug pane or other techniques.
3. A way to define a more global try/catch exception handler.
4. Ability to debug through the Android library source code.
Not Available:
1. A non-invasive way to view the contents of an Exception or where the Exception happened.
hey,
Ineresting question. Well, first tip, you can filter what logcat tells you. For instance, you make it just show you errors by clickin in the red (e).
It also tells you where the error happened if you run your app in debug mode. It can either point you directly to your code or to android sdk. Knowing what android package caused the error is a big help.
These two just pop into my mind. hope it helps!
I was running into the same issue and found the following by Steve H. that helped out:
What happens is that when the debugger
is attached, the exception logs don't
get posted to LogCat until you
terminate the application from within
the Debug perspective. This happens
because the application doesn't
actually crash until the debugger
detaches. – Steve H Mar 31 at 15:47
------ yup, that did it. Now I see the same exception. AFTER I let the
program run through it's full crash
and exit process. It should display
that info when it halts my program and
brings up the IDE debugger screens.
Not leave me wondering and wasting my
time with more clicking around.
Eclipse has a long way to go it seems
to compete with the likes of Visual
Studio. Let's hope my patience for it
outlasts my project. Thanks for the
feedback. :) – Sebastian Dwornik Mar
31 at 17:35
Link to Question: What's wrong with debugging in Eclipse on Android?
Generally if anything throws an exception then you should probably be catering for that situation anyway, however putting try/catch blocks is a decent way of finding the specific problem.
I've found that if you don't put something in the catch block then you can't evaluate the exception in the watch variables window in eclipse. So i always put a Log call in and set a break point on that line.
public void onCreate(Bundle savedInstanceState) {
try{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}catch(Exception exception)
{
// put break point on line below so you can evaluate exception in debug mode.
Log.e(TAG, "Set content exception "+ exception.getMessage());
// note some exceptions return null on getMessage();
}
Log.d("HelloWorldActivity.onCreate()", "setContentView() completed");
}
So if your stack trace is huge then this will help. Other developers have also found that getting the source code for the sdk means you can view where the error is thrown in the main sdk code. I've not done this though.
Exceptions not caught with try/catch are errors and break the normal flow of the program.
Running in debug mode is just clicking in the bug button. I don't know if there are any "special" debug libraries. But when working with android, all "libraries" are open source so you can pretty much view anything.
The good thing about debug mode is that when an error occurs, your app is frozen right in the limbo when the error occurs. You can set set breakpoints, change your code on the fly while your program is running, which is great (Well, you can't make drastic changes like changing a method name).
The way you treat bugs and errors in android, however, can be a bit different from .NET, since the model in each one is different.
When programming to windows, apps work like small islands. You have a much direct control over the code flow (ie: you can call a modal dialog to freeze codeflow while a user inputs some data) and you can make a totally functional program using just one thread. In android almost everything runs in it's own sync. And your app must be prepared to handle stuff like receiving a phone call in the middle of execution. So, you can apply this model to debugging also: Errors (that happen due to unforsen circumstances) tend to propagate much more than in other development ambient. The way those errors are handled is different too: this is apparent when you realize that your app still runs even after throwing an exception.
Some more useful tips:
You have a very powerful tool called Monkey, a stress tool that generates "pseudo-random streams of user events such as clicks, touches, or gestures, as well as a number of system-
level events".
LogCat indicates you the "cause" of the error. The line usually starts with Caused By. If you're interested in the cause rather than the consequence, you can further filter your error reports looking for "Caused by".
Last but not least, I find the old method of commenting lines and see what happens very useful to figure things out.
hope it helps