Why does Android Studio highlight “Theme” red in styles.xml?

问题

Red highlight means Cannot resolve symbol 'Theme'

Here are some configurations :

styles.xml

<style name="AppBaseTheme" parent="Theme.AppCompat.Light">
    <!--
        Theme customizations available in newer API levels can go in
        res/values-vXX/styles.xml, while customizations related to
        backward-compatibility can go here.
    -->
    <item name="android:windowNoTitle">true</item>
</style>

<!-- Application theme. -->
<style name="AppTheme" parent="AppBaseTheme">
    <item name="android:windowNoTitle">true</item>
</style>

.

AndroidManifest.xml

<uses-sdk android:minSdkVersion="8" android:targetSdkVersion="19" />

...

android:theme="@style/AppTheme">

.

build.gradle

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:appcompat-v7:19.0.0'
}

...

android {
    compileSdkVersion 19
    buildToolsVersion '20.0.0'
    defaultConfig {
    applicationId 'com.mobile.slider'
    minSdkVersion 8
    targetSdkVersion 19

.

MainActivity.java

public class MainActivity extends Activity {

---

It is working nice with my phone Nexus 4 whose android version is 4.4.4. Even though, There is no build problem, NoTitleWindow Mode doesn't work for
another phone which has 2.3.3 android version.

回答1:

This is how I solved it:

1. Go to your project directory (or to Project View)
2. Go into the .idea directory
3. Remove caches and libraries directories
4. File -> Invalidate Caches / Restart

Should be OK now.

回答2:

I had added appcompatv7 project as a module but I have forgotten to show it to my application module. Just I have realized and fixed. Now it doesn't alert me anymore. Thanks for your reply, tritop.

回答3:

It's very weird but I had the dependency in my .gradle.

To solve the issue I deleted it(//commented), sync, get all error because of it, put the dependency again, sync again. Then the problem was gone!

回答4:

Only this worked for me!

• Close project (File> Close Project)
• Import / Re-Open project again (NOT from Recent)

Error should be resolved now.

If that did not resolve, then try below

• Open build.gradle, remove appcompact-v7 dependency line and sync.
• Again add appcompact-v7 dependency and sync.

Issue must be resolved!

回答5:

Just delete the dependencies below and sync. Paste them again and sync.

implementation 'com.android.support:design:28.0.0'
implementation 'com.android.support:appcompat-v7:28.0.0'

来源：https://stackoverflow.com/questions/25265328/why-does-android-studio-highlight-theme-red-in-styles-xml