Error running 'app': Unknown error in Android studio 3.1

Question

I have updated my android studio to new stable version 3.1. After build project not able to run.

Let me know if anyone have face same issue or find any solution.

What happens if you do a manual build via `gradlew clean app:build` in the terminal? — Michael Dodd, Mar 27 '18 at 12:52
Let me try it, but i have clean build 2 times and gradlew build it taking around 20 minutes. — Devganiya Hitesh, Mar 27 '18 at 12:54
if gradle build taking too much time. try updating gradle version. — Pragnesh Ghoda シ, Mar 27 '18 at 12:55
As an alternative, you could try deleting and re-adding your run configurations. Haven't come across this issue, but that's helped me in the past when a project has refused to run for an unclear reason. — Michael Dodd, Mar 27 '18 at 12:56
Check this answer: https://stackoverflow.com/a/49508278/3806413 — 0xAliHn, Mar 27 '18 at 12:56
Build>Clean Project, Build>Rebuild Project solved same problem for me — MBDevelop, Mar 29 '18 at 14:48

score 30 · Accepted Answer · edited Mar 28 '18 at 06:07

30

Just go to "Run/edit configurations.../" and scroll down to bottom of the window and here you see an option "Before launch..." First, remove whatever already inside the little window and then click on (+) icon and select "Gradle-aware Make" and then type "assembleDebug" and select the first option or that you need. This will solve your problem.

edited Mar 28 '18 at 06:07

msp

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answered Mar 27 '18 at 19:29

Chelo

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Both this and @erine [comment](https://stackoverflow.com/a/49521024/1009782) where helpful. I deleted both build folders and it worked. – Alex Mar 28 '18 at 07:04
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This works for me. But could you please add a comment or link on what it actually does? To me it sounds like it is changing the may how it is built/assembled. – Erik Melkersson Mar 28 '18 at 18:46
both of the answer is not working for me. My classes are showing cannot resolve but the apk build is working. Android studio 3.1 and its killing me – Cyph3rCod3r Apr 02 '18 at 07:33

score 16 · Answer 2 · answered Mar 27 '18 at 19:29

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Try deleting both your build folders in your project manually and rebuild. This usually happens when you update gradle version, in my experience.

answered Mar 27 '18 at 19:29

ernie

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This, along with the selected answer, solved it for me. – Sub 6 Resources Mar 29 '18 at 03:27

xarlymg89 · Answer 3 · 2020-07-18T20:02:58.643

The solution that worked for me was a combination of other answers here.

I had upgraded to the most recent stable version of Android Studio at the time, 3.1. Along with that, Android Studio prompted a dialog asking me if I wanted to upgrade my Gradle from 3.x to 4.4, and I accepted as well.

After that I got the error of this question, and then I did this:

Open menu Run -> Edit configurations...
In the Before launch: section, select any options you have listed (each option has the Android symbol), and remove them with the - symbol
Add the option Gradle-aware Make, with the value assembleDebug
Clean and rebuild your whole project

for me, `assembleDebug` value does not required. just leave empty. — Youngjae, Apr 02 '18 at 14:49

score 2 · Answer 4 · answered Mar 28 '18 at 15:13

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just clean and rebuild your project

answered Mar 28 '18 at 15:13

Hoby

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score 1 · Answer 5 · answered Mar 27 '18 at 19:28

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I had the same problem. I change in build.gradle 'compile' with 'implementation', then clean and rebuild the project. Now it starts with no problem.

answered Mar 27 '18 at 19:28

Ionut

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score 0 · Answer 6 · answered Apr 01 '18 at 09:18

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Run "Build-> Clean Project" normally will fix this problem.

answered Apr 01 '18 at 09:18

Stephen Chang

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Normal clean build can not fix the problem if Gradle-aware Make changes are not done. – Devganiya Hitesh Apr 02 '18 at 05:38

Error running 'app': Unknown error in Android studio 3.1

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