Hi Elias,

The provided logs: 
2019-09-10 16:36:54.199 9400-9430/com.sample  E/GoLog: 2019/09/10 11:06:54 
test.go:134: testFunction [Test]
2019-09-10 16:36:54.199 9400-9430/com.sample  E/GoLog: 2019/09/10 11:06:54 
test.go:136: [Test] Now going to call a java system function 
(System.CurrentTimeMillis())..
2019-09-10 16:36:54.200 9400-9434/com.sample  E/GoLog: 2019/09/10 11:06:54 
test.go:138: [Test] Called java function return value is:  1568113614199

*In this you can see I am able to call System.CurrentTimeMillis() and 
printing in logs.*

*This is the next line of code where I am trying to call my own class java 
function from go: *
2019-09-10 16:36:54.200 9400-9434/com.sample  E/GoLog: 2019/09/10 11:06:54 
test.go:140: [Test] Now going to call my java function....

After this log I am actually calling like this: 
*RBinding.getStringFromJava() and it is crashing. *


I have one doubt when we build using gomobile in that I am giving the 
classpath to my .class java file. 
*Will it be included in .aar or I have to include that .class file along 
with .aar in my android application. *

Thanks.


On Tuesday, September 10, 2019 at 8:55:47 PM UTC+5:30, Elias Naur wrote:
>
> On Tue Sep 10, 2019 at 4:26 AM Jay Sharma wrote: 
> > ------=_Part_1258_983331168.1568114760099 
> > Content-Type: text/plain; charset="UTF-8" 
> > 
> > Hello @elias, 
> > 
> > I tried the following: 
> > 
> > 1. Created a java class : 
> > 
> > package reversebinding; 
> > 
> > public class RBinding { 
> >  public static String getStringFromJava() { 
> >         return "Hello from java !!"; 
> >     } 
> > } 
> > 
> > 2. Generated the .class file for this file. 
> > 
> > 3. Generated the android binding using gomobile tool and used 
> > -classpath="Path to my .class file" 
> > 
> > 4. Binding is generated successfully. 
> > 
> > *But when I used that generated (.aar) file in my android app and tried 
> to 
> > trigger the api it is crashing; * 
> > 
> > 2019-09-10 16:36:54.199 9400-9430/com.sample  E/GoLog: 2019/09/10 
> 11:06:54 
> > test.go:134: testFunction [Test] 
> > 2019-09-10 16:36:54.199 9400-9430/com.sample  E/GoLog: 2019/09/10 
> 11:06:54 
> > test.go:136: [Test] Now going to call a java system function 
> > (System.CurrentTimeMillis())..... 
> > 2019-09-10 16:36:54.200 9400-9434/com.sample  E/GoLog: 2019/09/10 
> 11:06:54 
> > test.go:138: [Test] Called java function return value is:  1568113614199 
> > 2019-09-10 16:36:54.200 9400-9434/com.sample  E/GoLog: 2019/09/10 
> 11:06:54 
> > test.go:140: [Test] Now going to call my java function..... 
> > 2019-09-10 16:36:54.203 9400-0/com.sample  E/Go: panic: runtime error: 
> > invalid memory address or nil pointer dereference 
> > 2019-09-10 16:36:54.203 9400-0/com.sample  E/Go: [signal SIGSEGV: 
> > segmentation violation code=0x1 addr=0x0 pc=0x7568010708] 
> > 2019-09-10 16:36:54.203 9400-0/com.sample  E/Go: goroutine 17 [running, 
> > locked to thread]: 
> > 2019-09-10 16:36:54.203 9400-0/com.sample  E/Go: 
> > test.testFunction(0x4000000738) 
> > 2019-09-10 16:36:54.203 9400-0/com.sample  E/Go:     
> > /home/test/2019/test/test.go:141 +0x190 
> > 2019-09-10 16:36:54.203 9400-0/com.sample  E/Go: 
> > main.proxytest__testFunction(...) 
> > 2019-09-10 16:36:54.203 9400-0/com.sample com.sample E/Go:     
> > /tmp/gomobile-work-071468276/src/gobind/go_testmain.go:199 
> > 2019-09-10 16:36:54.203 9400-0/com.sample  E/Go: 
> > 
> main._cgoexpwrap_5427a26f9204_proxytest__testFunction(0x8020080280200802) 
> > 2019-09-10 16:36:54.203 9400-0/com.sample  E/Go:     _cgo_gotypes.go:606 
> > +0x1c 
> > 2019-09-10 16:36:54.204 9400-9423/com.sample  A/libc: Fatal signal 6 
> > (SIGABRT), code -6 in tid 9423 (Thread-2) 
> > 
>
> The error is arguably not very helpful. Are you sure there is not another 
> error 
> before the nil pointer exception? In any case, did you ensure that the 
> .class 
> is included in the Android apk? An easy check is to try to call your 
> method 
> from Java before trying from Go. 
>
> -- elias 
>

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