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karwosts

Debugging Android Exceptions

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Hi, getting started with Android Java Programming coming from C++ and visual studio. I'm writing some code and I keep getting exceptions, but I cannot figure out how to find the source at all through the IDE.

For example, I have a bug in a function filldata() where I am trying to call Float.toString() on a null value. When I hit this point, I get an exception thrown, and if I look in my variables window I see the exception 'e' is of type NullPointerException, which makes sense given that I'm trying to call a function on a null value.

However, I have no idea how I should be tracking these down. The only way I was able to find the line was by stepping through the program line by line until I hit the exception. When I hit the breakpoint, I look at the call stack and there's not a single line in it that references any of my source code.

I feel like I must be missing something, because I've debugged several exceptions so far, but each one takes me 20m to find, because the call stack doesn't give me any information about where I am. Always just a bunch of lines about "ActivityThread".

Where is the actual call stack that says from what function the exception was thrown, etc?



Thread [<1> main] (Suspended (exception RuntimeException))
ActivityThread.performLaunchActivity(ActivityThread$ActivityClientRecord, Intent) line: 1696
ActivityThread.handleLaunchActivity(ActivityThread$ActivityClientRecord, Intent) line: 1716
ActivityThread.access$1500(ActivityThread, ActivityThread$ActivityClientRecord, Intent) line: 124
ActivityThread$H.handleMessage(Message) line: 968
ActivityThread$H(Handler).dispatchMessage(Message) line: 99
Looper.loop() line: 130
ActivityThread.main(String[]) line: 3806
Method.invokeNative(Object, Object[], Class, Class[], Class, int, boolean) line: not available [native method]
Method.invoke(Object, Object...) line: 507
ZygoteInit$MethodAndArgsCaller.run() line: 839
ZygoteInit.main(String[]) line: 597
NativeStart.main(String[]) line: not available [native method]

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I don't have experience with Android. However, if you allow that suspended thread to continue - this usually results in the full exception stack trace being printed somewhere.

If not, you can catch all exceptions somewhere high enough, call e.printStackTrace() and re-throw the exception (possible wrapped in a RuntimeException). It will include the exact line that created the NullPointerException.

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