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

Question

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.

Answer 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.

Answer 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.