material-components / material-components/material-components-android

[CoordinatorLayout] HeaderScrollingViewBehavior measure child spec overflow

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bug Widget: TopAppBar
Dominant language
Java
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Description

**Description:** When CoordinatorLayout's height is very small, for example `86dp`, and `headerHeight` in [link](https://github.com/material-components/material-components-android/blob/4c7be527751f1cb11f7c5f55ca5eecbb41c1620c/lib/java/com/google/android/material/appbar/HeaderScrollingViewBehavior.java#L85) is larger than CoordinatorLayout's height(like `90dp`), it will make `height` in [link](https://github.com/material-components/material-components-android/blob/4c7be527751f1cb11f7c5f55ca5eecbb41c1620c/lib/java/com/google/android/material/appbar/HeaderScrollingViewBehavior.java#L89) a negative value(90dp - 86dp = -4dp). `heightMeasureSpec` in [link](https://github.com/material-components/material-components-android/blob/4c7be527751f1cb11f7c5f55ca5eecbb41c1620c/lib/java/com/google/android/material/appbar/HeaderScrollingViewBehavior.java#L91) will be overflow and make second child in CoordinatorLayout measure incorrectly.

If seond child view is a RecyclerView or ListView with many item in it, it will make RecyclerView onMeasure spends lots of time. Because measureSpec overflow will provide a huge height measure size, and make RecylerView layout all item in it's adapter.

**Expected behavior:** `height` should not be negative, or `heightMeasureSpec` 's size should not be overflow
**Source code:** https://github.com/material-components/material-components-android/blob/master/lib/java/com/google/android/material/appbar/HeaderScrollingViewBehavior.java#L89

**Android API version:** Android 11

**Material Library version:** 1.5.0

**Device:** Xiaomi Civi

To help us triage faster, please check to make sure you are using the [latest version](https://github.com/material-components/material-components-android/releases) of the library.

We also happily accept [pull requests](https://github.com/material-components/material-components-android/pulls).

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First steps

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Research direction

Start in lib/java/com/google/android/material/appbar/HeaderScrollingViewBehavior.java around the linked measurement code. Reproduce the issue with a small CoordinatorLayout whose height is smaller than its header, using a RecyclerView or ListView as the second child. Done means the child measurement does not overflow when the header is taller than the CoordinatorLayout and the list no longer receives an unexpectedly huge measure size.

Written by the indexing model from the issue text.

Assessment

Tech stack
android, java
Domain
mobile-dev
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Clearly specified
Newbie friendliness
35/100

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