I got the following error when building:

FATAL EXCEPTION: main
Process: com.example.materialcomponentsmotion, PID: 15554
android.view.InflateException: Binary XML file line #63 in com.example.materialcomponentsmotion:layout/fragment_email: Binary XML file line #63 in com.example.materialcomponentsmotion:layout/fragment_email: Error inflating class ImageButton
Caused by: android.view.InflateException: Binary XML file line #63 in com.example.materialcomponentsmotion:layout/fragment_email: Error inflating class ImageButton
Caused by: java.lang.NumberFormatException: For input string: "?2130969008"
at jdk.internal.math.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:2054)
at jdk.internal.math.FloatingDecimal.parseFloat(FloatingDecimal.java:122)      
.
.
.                                                                                       

As you can see, there is a problem in line 63.

fragment_email.xml

<ImageButton
    android:id="@+id/navigation_icon"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:padding="@dimen/grid_2"
    app:layout_constraintEnd_toEndOf="@+id/sender_profile_image_view"
    app:layout_constraintStart_toStartOf="@+id/sender_profile_image_view"
    app:layout_constraintTop_toTopOf="@+id/subject_text_view"
    android:alpha="?attr/emphasisMediumAlpha"
    android:background="?attr/actionBarItemBackground"
    android:contentDescription="@string/navigate_back_icon_content_desc"
    app:srcCompat="@drawable/ic_arrow_down" />

Line 63 is the app:src attribute of the ImageButton.

But it wasn’t a problem with line 63.

I thought this was the problem for a long time, but when I deleted the android:alpha="?attr/emphasisMediumAlpha" line and ran it, The build has been completed.

This is code from CodeLab

Why does it cause an error?