Unknown attribute android:layout_width, layout_height, id, gravity, layout_gravity, padding

Getting Unknown attribute error on all android tag.
In layout XML, Auto suggestion is not showing all attributes (like layout_width, layout_height, orientation, orientation & all others android attributes.)

Here is a Snap shot

Things i have done to resolve this issue.

Clean Build & Rebuild
Deleted .idea file
Invalidated Caches/ Restart.. option
Turn On Power Save Mode.

SDk is up to date.

In App Level Gridle

apply plugin: 'com.android.application'

android {
    compileSdkVersion 23
    buildToolsVersion "23.0.2"

    defaultConfig {
        applicationId "com.example.abhishek.ondemandservice"
        minSdkVersion 15
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'),     'proguard-rules.pro'
        }
    }
}

Application level Gride.

buildscript {
    repositories {
        maven { url "http://dl.bintray.com/populov/maven" }
        jcenter()
        mavenCentral()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:1.5.0'

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        maven { url "http://dl.bintray.com/populov/maven" }
        jcenter()
        mavenCentral()
    }
}

Just go to Tools->Android->Sync Project with Gradle Files

Mohamed Akl

The only thing that worked for me was cleaning the following folders:

c:\Users\<user>\.gradle\caches\
c:\Users\<user>\.AndroidStudio3.2\system\caches\

Android Studio will just redownload the libraries and caches them which will enable everything back to normal.

Source: https://stackoverflow.com/a/53053438/7515903

Credits: @alexuz

To fix, change something in your gradle file, then sync gradle again. This worked for me.

Credit: https://stackoverflow.com/a/47500156/5673746

I tried:

Removing the build folders
Cleaning the project
Sync Project with Gradle Files

But nothing worked. Finally using File > Invalidate caches fixed the error.

I too encountered this..

Just delete the .idea folder that is in the project location
Build > Clean Project
Then change something in the app level gradle

Then android studio will ask you to sync the project. Go ahead and sync, the problem will be gone

Had the same issue, but after a reinstall of visual studio, so what helped for me on Android studio 3.2, was to go and upgrade the target version to 28 and compile version 28. Was at version 27 before.

I had to upgrade these packages as well

implementation "com.android.support:support-v4:28.0.0"
implementation 'com.android.support:support-core-ui:28.0.0'

After Gradle had synced then it worked for me.

Mohammad Hadi

if non of above answers dosn't work do these steps:

first close android studio.
than just go to windows>User or AppData>local> and delete androidstudio last version folder
reopen androidstuduio and set default settings

In my case none of the above solutions worked for me, but changing the minSdkVersion to a higher version and doing a gradle sync after that did the trick, maybe this would be useful to somebody.

Any of these ways will possibly fix your problem (unknown attribute android:layout-width)

Sync project with Gradle file (File -> Sync project with Gradle files)
Invalidate cache and restart (File -> Invalidate cache and restart -> Invalidate and restart)
Delete .gradle and .idea file from the project folder and rebuild the project.
Delete caches folder from Android studio (.AndroidStudio3.2 -> system -> caches)

Hulu

None of the existing suggestion works for me. I solved this issue by reinstalling Android Studio. Really weird.

I had to