How does setting baselineAligned to false improve performance in LinearLayout?

Question

I was just building some UI in xml, and Lint gave me a warning and said to set android:baselineAligned to false to improve performance in ListView.

The docs for the Lint changes that added this warning say

Layout performance: Finds LinearLayouts with weights where you should set android:baselineAligned="false" for better performance, and also finds cases where you have nested weights which can cause performance problems.

Can somebody explain why this improves performance, specifically when weight is involved?

score 175 · Accepted Answer · edited Sep 18 '16 at 05:17

175

By setting android:baselineAligned="false" , you're preventing the extra work your app's layout has to do in order to Align its children's baselines; which can obviously increase the performance. (Fewer unnecessary operations on UI => Better performance)

edited Sep 18 '16 at 05:17

Clyde

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answered Feb 16 '12 at 23:42

Nima

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That part is obvious. What I was trying to get at is why is this only a performance improvement when weight is involved? – Christopher Perry Feb 17 '12 at 02:02
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Because linearlayout only need to calculate the baseline when weights are involved. Its like a smart feature which actually can be annoying. – Warpzit Feb 23 '12 at 08:33
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The term baseline comes from typography. It's the invisible line letters in text sit on. http://en.wikipedia.org/wiki/Baseline_%28typography%29 – Zsolt Safrany Sep 29 '12 at 12:26
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So if it's a performance improvement, that means work that's normally done isn't being done anymore. What are the side-effects of this? Does the work that we're now avoiding have the capability of yielding different results? – lhunath Mar 26 '13 at 20:29
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@lhunath according to the documentation, The default is set to **true**. this forces the baseline of any UI text to align themselves with eachother. For example think about buttons,you have like two buttons with same width/height on the same line but one of them have a longer text, because of `baselineAlined="true"`, the button with longer text can end up moving around to align it's text with other buttons. For a better example, check out [this post](http://udinic.wordpress.com/tag/baselinealigned/) – Nima Mar 27 '13 at 16:11
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Here is the visual solution! http://stackoverflow.com/a/38007282/2959200 – Sjd Sep 27 '16 at 06:46
@lhunath yes it can result in different layout as I've experienced cases where I discovered unexpectedly that the baseline is not just a property of text views but is also calculated for the layout that wraps them, example would be LinearLayout containing two RelativeLayouts each containing a Button. The RelativeLayouts calculate a baseline from their contents, you will still get the warning but the layout changes if you make the change. – Robert Tuck Feb 24 '17 at 11:51
Another nice article with visual explanation: https://medium.com/@pareshmayani/androiddev-tip-set-android-baselinealigned-false-on-this-element-for-better-performance-810fa3148043 – Jérémy Reynaud Jan 31 '19 at 11:23

score 22 · Answer 2 · edited Aug 21 '14 at 12:32

how android:baselineAligned="false" help . It may not be the answer but help to get concept.

I've just managed to get 3 items (icon, text, button) centered vertically in horizontal LinearLayout.

This may seem simple, but in reality specifying android:gravity="center_vertical" as LinearLayout attribute is not enough - icon is centered, but text and button are not. This is because (presumably) text have a baseline, and centering algorithm uses it instead of 'real' vertical center. But what is worse - button (which comes next to text) is centered using text's baseline!

Specifying android:baselineAligned="false" in LinearLayout turns this off, and everything centers correctly.

score 17 · Answer 3 · edited Apr 19 '17 at 12:19

// Baseline alignment requires to measure widgets to obtain the
                // baseline offset (in particular for TextViews). The following
                // defeats the optimization mentioned above. Allow the child to
                // use as much space as it wants because we can shrink things
                // later (and re-measure).
                if (baselineAligned) {
                    final int freeSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED);
                    child.measure(freeSpec, freeSpec);
                }

https://github.com/android/platform_frameworks_base/blob/master/core/java/android/widget/LinearLayout.java#L1093

How does setting baselineAligned to false improve performance in LinearLayout?

3 Answers3

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