What is the difference between android:contentDescription="@null" and tools:ignore="ContentDescription"? Use android:importantForAccessibility="no"?

Question

Take this android layout XML snippet for example:

<ImageView
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_gravity="center"
        android:layout_weight="1"
        android:padding="10dp"
        app:srcCompat="@drawable/bitcoin"
        android:contentDescription="@null"
        android:importantForAccessibility="no"
        tools:ignore="ContentDescription" />

What is the difference between android:contentDescription="@null" and tools:ignore="ContentDescription"?

I know both of them are used to indicate that a certain non-textual element carries no meaning and is only meant for decoration. Is there an advantage of using one over the other, should I use both, is it preference, or is one considered better and newer than the other?

Also, should I use android:importantForAccessibility="no" or is using all three attributes/properties simply overkill?

Answer 1

What is the difference between android:contentDescription="@null" and tools:ignore="ContentDescription"?

android:contentDescription="@null"

• Used to indicate that a certain non-textual element carries no meaning and is only meant for decoration.

tools:ignore="ContentDescription"

• For graphical elements, such as ImageView and ImageButton. If you do not set their respective android:contentDescription XML attributes, a lint warning message will be displayed.

  "Missing contentDescription attribute on image"

• To suppress this lint warning message then you must use tools:ignore="ContentDescription" in XML.

I know both of them are used to indicate that a certain non-textual element carries no meaning and is only meant for decoration. Is there an advantage of using one over the other, should I use both, is it preference, or is one considered better and newer than the other?

No, they are different from each other in term of usage, for example

<ImageView 
    android:layout_width="200dp"
    android:layout_height="300dp"
    android:id="@+id/image_user_avatar"
    android:contentDescription="User avatar"
    tools:ignore="ContentDescription" />

When running the app with TalkBack, it will speak "User avatar".

Should I use android:importantForAccessibility="no"?

If your app only supports devices running Android 4.1 (API level 16) or higher, you can set these elements' android:importantForAccessibility XML attributes to "no" instead of android:contentDescription="@null.

Update

So basically tools:ignore="ContentDescription" is only for the compiler and android:contentDescription="@null" is for user user?

Yes, it is.

Also, my 'minSdk' is 14 and my 'targetSdk' is 28. Can I still set both android:importantForAccessibility="no" and android:contentDescription="@null"?

Yes, you can set both of them but if you run the app on device whose SDK below 16, android:importantForAccessibility="no" will be ignored.

Will android:contentDescription="@null" have the same effect as android:importantForAccessibility="no" for devices running Android 4.1 or higher?

They have slightly difference.

android:contentDescription="@null": The view with this attribute still highlighted when users move finger on it and Accessibility Services will speak out loud dummy text such as "Button", etc.

android:importantForAccessibility="no": The view with this attribute is disabled by the app so it will not highlighted when users move finger on and ignored by Accessibility Services as well.