Duplicate android:id in Layout

ID

kotlin.android_duplicate_ids

Severity

low

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Kotlin

Tags

android, best-practice, reliability

Description

Reports elements in the same Android layout XML file that declare the same android:id value. Duplicate IDs make findViewById return an arbitrary match and can crash fragment-transaction APIs.

Rationale

When two or more elements share the same android:id in a single layout, only one of them can be reliably found at runtime. Activity.findViewById() and View.findViewById() return whichever match the framework encounters first during tree traversal, making the result non-deterministic if the layout is restructured. Fragment transactions that reference the duplicated ID may target the wrong container, leading to crashes or misplaced fragments.

<!-- Bad: two elements share the same ID -->
<LinearLayout ...>
    <TextView android:id="@+id/title" android:text="First" />
    <TextView android:id="@+id/title" android:text="Second" />
</LinearLayout>

Remediation

Assign a unique android:id to each element within the same layout file.

<!-- Good: unique IDs -->
<LinearLayout ...>
    <TextView android:id="@+id/title" android:text="First" />
    <TextView android:id="@+id/subtitle" android:text="Second" />
</LinearLayout>

References