Fatal Exception: java.lang.UnsupportedOperationException: Failed to resolve attribute at index 6: TypedValue{t=0x2/d=0x101009b a=1}

The main cause of this problem seems to be a missing style/theme in the AppCompat library, or a bug in the library. It happens when using either AppCompatEditText or AppCompatAutoCompleteTextView and a WebView is also added to the layout (AdMob ads are WebViews). It happens on several versions of AppCompat, like 23, 24, 25, 26.

It can be seen more clearly in a useful demo app that someone made on Github:

1. Clone the repo and open in Android Studio v2.3 or higher.
2. Android Studio should prompt to update the gradle dependencies and buildToolsVersion in this project, something like this:

build.gradle:

dependencies {
    classpath 'com.android.tools.build:gradle:2.3.3'
    ...
}

app/build.gradle:

buildToolsVersion '25.0.0'

gradle-wrapper.properties:

distributionUrl=https\://services.gradle.org/distributions/gradle-3.3-all.zip

3. Update the dependencies then build the project. Run the app on Android 7 emulator or device, with a stock Android keyboard. Set the system language to English.
4. On the input field, type the letters ‘tttf’ on the Android keyboard. Then press space. The word should be underlined as misspelled.
5. Now click one of the letters (not long-press) to try to move the cursor. It should crash the app – like this:

The solution (from here) is to explicitly add both "colorAccent" and "android:colorAccent" in your main AppTheme, in styles.xml:

<style name="AppTheme" parent="Theme.AppCompat">
    <item name="colorPrimary">@color/colorPrimary</item>
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="colorAccent">@color/colorAccent</item>
    <item name="android:colorAccent" tools:targetApi="lollipop">@color/colorAccent</item>
</style>

or

<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <item name="colorPrimary">@color/colorPrimary</item>
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="colorAccent">@color/colorAccent</item>
    <item name="android:colorAccent" tools:targetApi="lollipop">@color/colorAccent</item>
</style>

This will now work to allow the stock spelling suggestions popup to appear, and no more crashing.

Similar reports or duplicates:

• Android N crashes in TextAppearanceSpan
• https://meta.stackexchange.com/questions/292199/android-app-crashes-when-tapping-on-red-underlined-by-the-spell-checker-text-w
• https://issuetracker.google.com/issues/37118322