Android Cannot resolve symbol '?attr/selectabl

问题:

<android.support.v7.widget.CardView
    android:id="@+id/card_view"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginLeft="@dimen/card_outer_padding"
    android:layout_marginTop="@dimen/card_outer_padding"
    android:layout_marginRight="@dimen/card_outer_padding"
    android:layout_marginBottom='@{model.cardBottomMargin}'
    android:foreground="?attr/selectableItemBackground"
    android:onClick="@{model::onCardClick}"
    app:cardElevation="2dp"
    app:cardCornerRadius="2dp"
    app:cardUseCompatPadding="true">
</android.support.v7.widget.CardView>

I got this error message

Cannot resolve symbol ?attr/selectableItemBackground Validates resource references inside Android XML files.

<TextView
    android:id="@+id/country_name"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginRight="40dp"
    android:text="@{model.name}"
    style="@style/TextAppearance.AppCompat.Headline"
    tools:text="Country"/>

And, I got a similar error for the above as well

Cannot resolve symbol '@style/TextAppearance.AppCompat.Headline'
Validates resource references inside Android XML files.

Any pointer would be great! Thank you! It seems to be related to this thread but no solution was provided:

回答1:

I believe this is a communication problem with the IDE and Android Gradle Plugin. In any case, the only way I've reliably found to resolve this is to delete the problematic libs in the .idea/libraries/ folder.

So, for you, since the lint checks aren't recognizing ?attr/selectableItemBackground

1. LOCATE the Gradle__com_android_support_xxx.xml files
2. DELETE those files
3. SYNC IDE with file system
4. SYNC project with Gradle files
5. REBUILD your project

You can sync by clicking on 'File' at the top by the toolbar and selecting "Sync with File System" and then afterwards selecting "Sync project with gradle files".

I've tried other suggested solutions - had the appcompat-v7 dependency in my module build.gradle file & the google() repository as the first line in the project build.gradle dependencies. Nada.

These solutions also haven't helped...

• Invalidating the caches/restarting didn't work.
• Cleaning/Rebuilding the project.

回答2:

For version Lollipop and higher use this:

android:foreground="?android:attr/selectableItemBackground"

for Pre-Lollipop use this:

android:foreground="?attr/selectableItemBackground"

回答3:

2 options:

Option 1

Another possible reason is: Google's maven repository is not set for the build script.

Open your project's main build.gradle add this line:

buildscript {
    repositories {
        google()  <-- this
        // Be also sure that google() is before jcenter()
    }
}

Without this, it may not be able to download the Android Studio Gradle plugin 3.0+. It's not distributed in jCenter but in the Google's maven repository.

Option 2

Run this command in root of project and resync project

Linux:

rm .idea/libraries/Gradle__com_android_support_*.xml

Windows:

del .idea\libraries\Gradle__com_android_support_*.xml

回答4:

I faced with same error after updating Kotlin. Solved with "Invalidate caches/Restart"

---

UPDATE Today this solution did not helped me. But the solution of this question did: Android Studio 3.1 Cannot Resolve Symbol (Themes, Widget, attr, etc.)

回答5:

Both resources are defined with the Android Support Library and since these symbols cannot be resolved, it seems like you're missing to define the support dependency.

dependencies {
    compile "com.android.support:appcompat-v7:$androidSupportVersion"
}

回答6:

In my case help adding maven to build.gradle Project in buildscripts.repositories AND allprojects.repositories. It looks like this:

google()
maven { url 'https://maven.google.com' }
jcenter()

回答7:

I have solved by,

• Deleting the .idea folder in project explorer.
• Invalidate Caches/Restart
• Refresh Project Gradle

回答8:

This is what solved to me:

1. Close Android Studio
2. Delete .idea directory in the root project directory

3. Reimport the project