(#) Unnecessary parent layout !!! WARNING: Unnecessary parent layout This is a warning. Id : `UselessParent` Summary : Unnecessary parent layout Severity : Warning Category : Performance Platform : Android Vendor : Android Open Source Project Feedback : https://issuetracker.google.com/issues/new?component=192708 Since : Initial Affects : Resource files Editing : This check runs on the fly in the IDE editor Implementation : [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/UselessViewDetector.java) Tests : [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/UselessViewDetectorTest.kt) Copyright Year : 2011 A layout with children that has no siblings, is not a scrollview or a root layout, and does not have a background, can be removed and have its children moved directly into the parent for a flatter and more efficient layout hierarchy. (##) Example Here is an example of lint warnings produced by this check: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text res/layout/useless.xml:13:Warning: This LinearLayout layout or its FrameLayout parent is unnecessary [UselessParent] <LinearLayout ------------ res/layout/useless.xml:47:Warning: This LinearLayout layout or its FrameLayout parent is unnecessary; transfer the background attribute to the other view [UselessParent] <LinearLayout ------------ res/layout/useless.xml:65:Warning: This LinearLayout layout or its FrameLayout parent is unnecessary; transfer the background attribute to the other view [UselessParent] <LinearLayout ------------ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Here is the source file referenced above: `res/layout/useless.xml`: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~xml linenumbers <merge xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" > <!-- Neither parent nor child define background: delete is okay --> <FrameLayout android:id="@+id/LinearLayout" android:layout_width="match_parent" android:layout_height="match_parent" > <LinearLayout android:layout_width="match_parent" android:layout_height="match_parent" > <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" /> </LinearLayout> </FrameLayout> <!-- Both define background: cannot be deleted --> <FrameLayout android:layout_width="match_parent" android:layout_height="match_parent" android:background="@drawable/bg" > <LinearLayout android:layout_width="match_parent" android:layout_height="match_parent" android:background="@drawable/bg" > <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" /> </LinearLayout> </FrameLayout> <!-- Only child defines background: delete is okay --> <FrameLayout android:layout_width="match_parent" android:layout_height="match_parent" > <LinearLayout android:layout_width="match_parent" android:layout_height="match_parent" android:background="@drawable/bg" > <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" /> </LinearLayout> </FrameLayout> <!-- Only parent defines background: delete is okay --> <FrameLayout android:layout_width="match_parent" android:layout_height="match_parent" android:background="@drawable/bg" > <LinearLayout android:layout_width="match_parent" android:layout_height="match_parent" > <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" /> </LinearLayout> </FrameLayout> <!-- Leaf cannot be deleted because it has a background --> <FrameLayout android:layout_width="match_parent" android:layout_height="match_parent" android:background="@drawable/bg" > </FrameLayout> <!-- Useless leaf --> <FrameLayout android:layout_width="match_parent" android:layout_height="match_parent" > </FrameLayout> </merge> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You can also visit the [source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/UselessViewDetectorTest.kt) for the unit tests for this check to see additional scenarios. The above example was automatically extracted from the first unit test found for this lint check, `UselessViewDetector.testUseless`. To report a problem with this extracted sample, visit https://issuetracker.google.com/issues/new?component=192708. (##) Suppressing You can suppress false positives using one of the following mechanisms: * Adding the suppression attribute `tools:ignore="UselessParent"` on the problematic XML element (or one of its enclosing elements). You may also need to add the following namespace declaration on the root element in the XML file if it's not already there: `xmlns:tools="http://schemas.android.com/tools"`. ```xml <?xml version="1.0" encoding="UTF-8"?> <AbsoluteLayout xmlns:tools="http://schemas.android.com/tools" tools:ignore="UselessParent" ...> ... </AbsoluteLayout> ``` * Using a special `lint.xml` file in the source tree which turns off the check in that folder and any sub folder. A simple file might look like this: ```xml <?xml version="1.0" encoding="UTF-8"?> <lint> <issue id="UselessParent" severity="ignore" /> </lint> ``` Instead of `ignore` you can also change the severity here, for example from `error` to `warning`. You can find additional documentation on how to filter issues by path, regular expression and so on [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html). * In Gradle projects, using the DSL syntax to configure lint. For example, you can use something like ```gradle lintOptions { disable 'UselessParent' } ``` In Android projects this should be nested inside an `android { }` block. * For manual invocations of `lint`, using the `--ignore` flag: ``` $ lint --ignore UselessParent ...` ``` * Last, but not least, using baselines, as discussed [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).