Eclipse logcat debugging
I have a beginner question, I want to debug my app and i don't know how to use the Logcat properly.
Right now, I am getting this error and i don't know what it means.
How can i use this information? Is there a tutorial somewhere i can watch?
Thanks for your help.
09-23 11:27:55.968: E/AndroidRuntime(807): FATAL EXCEPTION: main
09-23 11:27:55.968: E/AndroidRuntime(807): java.lang.NullPointerException
09-23 11:27:55.968: E/AndroidRuntime(807): at com.uniqueapps.runner.Start.onClick(Start.java:49)
09-23 11:27:55.968: E/AndroidRuntime(807): at android.view.View.performClick(View.java:4240)
09-23 11:27:55.968: E/AndroidRuntime(807): at android.view.View$PerformClick.run(View.java:17721)
09-23 11:27:55.968: E/AndroidRuntime(807): at android.os.Handler.handleCallback(Handler.java:730)
09-23 11:27:55.968: E/AndroidRuntime(807): at android.os.Handler.dispatchMessage(Handler.java:92)
09-23 11:27:55.968: E/AndroidRuntime(807): at android.os.Looper.loop(Looper.java:137)
09-23 11:27:55.968: E/AndroidRuntime(807): at android.app.ActivityThread.main(ActivityThread.java:5103)
09-23 11:27:55.968: E/AndroidRuntime(807): at java.lang.reflect.Method.invokeNative(Native Method)
09-23 11:27:55.968: E/AndroidRuntime(807): at java.lang.reflect.Method.invoke(Method.java:525)
09-23 11:27:55.968: E/AndroidRuntime(807): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
09-23 11:27:55.968: E/AndroidRuntime(807): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
09-23 11:27:55.968: E/AndroidRuntime(807): at dalvik.system.NativeStart.main(Native Method)
09-23 11:27:59.528: I/Process(807): Sending signal. PID: 807 SIG: 9
09-23 11:28:01.108: D/gralloc_goldfish(877): Emulator without GPU emulation detected.
09-23 11:54:55.318: D/gralloc_goldfish(937): Emulator without GPU emulation detected.
09-23 11:54:57.887: I/Choreographer(937): Skipped 35 frames! The application may be doing too much work on its main thread.
09-23 11:55:03.118: D/dalvikvm(937): GC_FOR_ALLOC freed 89K, 7% free 2928K/3136K, paused 39ms, total 72ms
09-23 11:55:05.858: D/AndroidRuntime(937): Shutting down VM
09-23 11:55:05.858: W/dalvikvm(937): threadid=1: thread exiting with uncaught exception (group=0x414c4700)
09-23 11:55:05.868: E/AndroidRuntime(937): FATAL EXCEPTION: main
09-23 11:55:05.868: E/AndroidRuntime(937): java.lang.NullPointerException
09-23 11:55:05.868: E/AndroidRuntime(937): at com.uniqueapps.runner.Start.onClick(Start.java:49)
09-23 11:55:05.868: E/AndroidRuntime(937): at android.view.View.performClick(View.java:4240)
09-23 11:55:05.868: E/AndroidRuntime(937): at android.view.View$PerformClick.run(View.java:17721)
09-23 11:55:05.868: E/AndroidRuntime(937): at android.os.Handler.handleCallback(Handler.java:730)
09-23 11:55:05.868: E/AndroidRuntime(937): at android.os.Handler.dispatchMessage(Handler.java:92)
09-23 11:55:05.868: E/AndroidRuntime(937): at android.os.Looper.loop(Looper.java:137)
09-23 11:55:05.868: E/AndroidRuntime(937): at android.app.ActivityThread.main(ActivityThread.java:5103)
09-23 11:55:05.868: E/AndroidRuntime(937): at java.lang.reflect.Method.invokeNative(Native Method)
09-23 11:55:05.868: E/AndroidRuntime(937): at java.lang.reflect.Method.invoke(Method.java:525)
09-23 11:55:05.868: E/AndroidRuntime(937): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
09-23 11:55:05.868: E/AndroidRuntime(937): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
09-23 11:55:05.868: E/AndroidRuntime(937): at dalvik.system.NativeStart.main(Native Method)
09-23 11:55:09.657: D/gralloc_goldfish(961): Emulator without GPU emulation detected.
09-23 12:04:20.418: D/gralloc_goldfish(1006): Emulator without GPU emulation detected.
09-23 12:04:27.118: D/dalvikvm(1006): GC_FOR_ALLOC freed 96K, 7% free 2919K/3136K, paused 40ms, total 72ms
09-23 12:04:30.337: D/AndroidRuntime(1006): Shutting down VM
09-23 12:04:30.357: W/dalvikvm(1006): threadid=1: thread exiting with uncaught exception (group=0x414c4700)
09-23 12:04:30.397: E/AndroidRuntime(1006): FATAL EXCEPTION: main
09-23 12:04:30.397: E/AndroidRuntime(1006): java.lang.NullPointerException
09-23 12:04:30.397: E/AndroidRuntime(1006): at com.uniqueapps.runner.Start.onClick(Start.java:49)
09-23 12:04:30.397: E/AndroidRuntime(1006): at android.view.View.performClick(View.java:4240)
09-23 12:04:30.397: E/AndroidRuntime(1006): at android.view.View$PerformClick.run(View.java:17721)
09-23 12:04:30.397: E/AndroidRuntime(1006): at android.os.Handler.handleCallback(Handler.java:730)
09-23 12:04:30.397: E/AndroidRuntime(1006): at android.os.Handler.dispatchMessage(Handler.java:92)
09-23 12:04:30.397: E/AndroidRuntime(1006): at android.os.Looper.loop(Looper.java:137)
09-23 12:04:30.397: E/AndroidRuntime(1006): at android.app.ActivityThread.main(ActivityThread.java:5103)
09-23 12:04:30.397: E/AndroidRuntime(1006): at java.lang.reflect.Method.invokeNative(Native Method)
09-23 12:04:30.397: E/AndroidRuntime(1006): at java.lang.reflect.Method.invoke(Method.java:525)
09-23 12:04:30.397: E/AndroidRuntime(1006): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
09-23 12:04:30.397: E/AndroidRuntime(1006): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
09-23 12:04:30.397: E/AndroidRuntime(1006): at dalvik.system.NativeStart.main(Native Method)
09-23 12:04:33.918: D/gralloc_goldfish(1030): Emulator without GPU emulation detected.
Solution 1:
After you see
FATAL EXCEPTION: main
you will see the problem, here a NPE
09-23 11:27:55.968: E/AndroidRuntime(807): java.lang.NullPointerException
then you find the first line that references your app. Here it is the following line
at com.uniqueapps.runner.Start.onClick(Start.java:49)
This says that in Start.java
something is null
in onClick()
at line 49. So you go to that line and see what could be null
...like a variable that tries to access a method such as setText()
, getText()
, or any Android or user defined method. Sometimes it is simple why it is null
and sometimes you have to trace back further to see what makes it null
.
Edit
If a variable is null
it is because it hasn't been initialized properly, or at all. So maybe you have a variable TextView tv;
but you never gave it a value by doing something like
tv = (TextView) findViewById(R.id.myTV);
if you try to do something like tv.setText("Some Text");
you will get a NPE
because you didn't initialize it with something like the above line of code. Or maybe you tried to initialize it and used the wrong id
like one from a different layout
. This will return null
and create a NPE
in the same way. This can be on any variable that you try to call a method on.