I'm familiar with almost all the basic layouts in Android & understand when they are to be used. I know that a RelativeLayout is to be used when elements in the UI are to positioned relative to each other, that a LinearLayout is to be used when UI elements are to be displayed vertically or horizontally. So I was wondering if the ease of development was the only factor that determined what layout should be selected or if there was any performance factor involved. I mean I can lay out two ImageViews vertically in Android using both LinearLayout and RelativeLayout, so why use a particular layout then?
There are some performance gains for avoiding certain things, such as nesting RelativeLayout (see this question). Also, the docs recommend making layouts shallow and wide, which can facilitated with RelativeLayout, again for performance reasons.
However, often thinking about such things will be premature optimization for simple layouts, and you should use whatever makes the most sense for the situation.
For a long time I heard that RelativeLayouts are slow. In a couple of talks I recall hearing that this type of layout calls onMeasure twice and that for some reason is a drag to performance.
However, I am taking a performance course at udacity and I watched the following video:
https://www.youtube.com/watch?time_continue=303&v=gK9tdeqqigE
Here, the instructor used the Hierarchy viewer tool to compare the rendering cost of the same viewgroup using a relative layout and nested linear layouts.
In the video, the relativelayout is the clear winner, which contradicts everything that I have heard until now about the issue.
Could you please help me to understand in which circumstances each approach is better?
Thank you
That's a very broad question and there's no single, simple answer. LinearLayout is generally simpler (and therefore faster) than RelativeLayout, but LinearLayout has a problematic case if you nest multiple of them inside each other, with weights on the same axis. Then it has to iteratively divide up the space and this takes lots of layout passes (it's so bad there's a lint warning against this).
Even when you avoid that case, then with nested LinearLayouts you will still have a deeper view hierarchy compared to using RelativeLayout, so while LinearLayout is faster, that balances out at some point.
So it becomes the same thing as with all things performance: the only way to be absolutely sure is to measure and see what happens.
I am freelancing to solve crash of an android app. It happens on startup, and I know it is because the activity_main.xml. It has too many views, too many nesting levels. Apart from that (wich I will try to reduce)
what are other strategies to improve layout performance in Android?
The user interface cannot be changed or simplified.
For example:
- for repeated elements (50 - 100), does using 'include' makes it faster?
- the same for defining properties in styles instead of in every item.
I have been recently working on improving performance of app and renderd a fast smooth UI let me share you my experience :
The vision of performance in terms of UI is:
Lower the latency of screen draws
Create fast, consistent frame rates to avoid jank/lag.
And there are some thumb rules for layouts .
Minimum view hierarchy.
minimum background drawbles
minimizing overdraw of window :
minimizing overdraw of Views
using drawble left instead of image and textview aligned horizontally.
using lists/recyclerview very often when repetitive view
and Many more . let me share some links which are really helpful
https://medium.com/#elifbon/android-application-performance-step-1-rendering-ba820653ad3#.pp7hpnv07
https://www.safaribooksonline.com/library/view/high-performance-android/9781491913994/ch04.html
https://riggaroo.co.za/optimizing-layouts-in-android-reducing-overdraw/
https://www.hackerearth.com/notes/rendering-performance-in-android-overdraw/
Letme know if it's helpful. Cheers
You can try following from https://developer.android.com,
Optimizing Layout
Inspect Your Layout
Revise Your Layout
Use Lint
AS well as
Improving Layout Performance
Optimizing Layout Hierarchies
Re-using Layouts with
Loading Views On Demand
Re-using Layouts with
I have answered a related question before and my advice is still applicable in this topic.
Handling loads:
Lazy Loading - Load only those piece of information that is really needed by now. Example : A Movie app: Load only those latest movies rather than those old movies unless the user told you to do so. The idea here is that decided only on which is necessary to load first and load other else later on. The lesser the load the greater the performance is while without sacrificing a good content.
Caching - If you keep on downloading things from your server chances are it might take too long to load and your splash screen will be visible for longer period of time or some of your UI might freeze specially when you do it in the Main thread. With caching you will need to fetch fewer data from the network since you've downloaded some of them already.
Things to consider in creating views.
Avoid a super deep nested views.
Avoid a deep nested weights.
For image loading use some popular library like Picasso, Glide etc.
does using 'include' makes it faster?
A bit, Reusing layouts is particularly powerful as it allows you create reusable complex layouts. For example, a yes/no button panel, or custom progress bar with description text. It also means that any elements of your application that are common across multiple layouts can be extracted, managed separately, then included in each layout. So while you can create individual UI components by writing a custom View, you can do it even more easily by re-using a layout file.
Source : Official docs
Addendum
When things are still wrong and the Android framework doesn't provide what you really need; the last approach is to create your own view via extending View or ViewGroup. Creating your own view/layout requires time and much effort but you gain more controls since it is your own view/layout implementation, let say you have the power to change the world.
Some commonly used android layouts such as
RelativeLayout and LinearLayout (when weights are nonzero)
have onMeasure() implementations that measure their children
twice, resulting in exponential running time when nested.
This is easily verifiable by emitting Log entries
from a leaf View's onMeasure()... it gets called 2depth
times.
Can someone give a clear and specific description as to why this is?
Most importantly, is this exponential behavior due to an important part
of the overall contract, or is it just an implementation detail
that might be optimized away? If it is believed to be unavoidable,
please give an example that requires it.
Such an example would greatly help me and others
who are grumbling that the "keep your layouts shallow"
mandate is burdensome and who are wondering
whether this is being driven simply by
not-yet-optimal algorithms in the core libraries,
or whether there really is a fundamental difficulty
blocking a fix.
Perhaps a minimal example would consist
of a Button inside a LinearLayout inside another LinearLayout
(with match_parent and weight=1 everywhere, to trigger
the full exponential behavior),
with some additional parameters or circumstances
making it clear that all four of the calls
to Button.onMeasure() are indeed meaningful and necessary.
My first guess would be that only two linear-time
traversals are really needed-- the first traversal to gather everyone's
preferred sizes, the second traversal to distribute slack
and/or shrinkage.
Other layout engines in the world, such as those for Tex and Swing and HTML,
seem to be able to routinely handle very deep hierarchies
having lots of alignment constraints and stretches,
without any exponential blowup, and I imagine that's how they work.
Please note, I don't want answers explaining how
the exponential blow-up occurs-- I understand that,
and there have been several posts already where that has been
asked and answered:
Why are nested weights bad for performance? Alternatives?
Android layout measuring time doubles with each step up the hierarchy
Layout Weight warning Nested weight bad performance
Efficiency of Android Layout hierarchy
http://android-developers.blogspot.com/2009/02/android-layout-tricks-1.html
My question is whether the recursive double-measuring is
fundamentally necessary/justified,
and if so, I'd like a clear explanation/example showing why.
Edit 2013/8/22: I think maybe my question is still not getting across.
I'll try to clarify and explain my motivation, more boldly this time.
Layout is not an exponentially hard problem,
as evidenced by efficient layout engines in the world, such as those for Tex and Swing and HTML.
So, what happened with LinearLayout,
and how should the android developer community proceed in response?
I am asking not in the spirit of laying blame,
but rather to understand and decide how to best move forward.
I can think of 4 possibilities:
Fix the performance bug in the core library, without changing any contracts
Change contracts as needed, and fix the performance bug in the
core library
Write an alternative to LinearLayout, that has its essential
features (namely distributing extra space among children in specified proportions) but without the performance bug, and use it for new apps
Continue to micromanage our layouts to work around the
performance bug for the rest of our android development careers.
(4) isn't a serious option for me personally.
Furthermore it seems clear to me that
changing the behavior of LinearLayout at this point is impractical,
so I don't believe (2) is a serious option either.
That leaves (1) and (3).
I'm capable and willing to do either of those personally, but which one?
Obviously (1) is far preferable if it's possible-- so, is it possible?
That seems to be the crucial blocking question that needs to be answered
in order to determine how to move forward.
I have spent some time in the core code
and the doc and it's not becoming clear,
so that is why I'm asking the question here.
In terms of measuring children twice, it's my understanding that this is what happens with LinearLayouts particularly when weights are involved. The best explanation I've found for this comes from RomainGuy in one of his presentations.
He has a slide about this and briefly speaks to it at 17:45. Feel free to rewind to get a bit of context though. You can find the video I'm referencing here: Devoxx'10 - Dive Into Android
Basically what he says is that on the first pass they calculate the total width or height depending on orientation of the LinearLayout, add the weights of the children, and find out how much space is left over, then on the second pass with that information they are able to properly divvy out all the remaining space to all the children. Simple enough.
I'd also like to point out though that yes, while it's very true that shallow layout hierarchies have less of a performance hit, if you are adding just 1 or 2 extra layers, you probably aren't going to see a big performance impact for the user. Once it's laid out, it's done. Even in ListView's if you properly use the given "convertView", and set up ViewHolder's, you're going to get good performance.
I'd encourage you to use DDMS and do a layout dump of some of Google's apps. They are very complex, and often times surprisingly deep, but they still get good performance. Don't be stupid with your layouts, but if it saves you time, adding an extra layout isn't the end of the world.
From here: http://developer.android.com/guide/topics/ui/how-android-draws.html
A parent View may call measure() more than once on its children. For example, the parent may measure each child once with unspecified dimensions to find out how big they want to be, then call measure() on them again with actual numbers if the sum of all the children's unconstrained sizes is too big or too small (that is, if the children don't agree among themselves as to how much space they each get, the parent will intervene and set the rules on the second pass).
It seems they view the measurement pass as a dialog between parent and children. In other words they opted for maximum flexibility instead of optimization. It still seems like they could optimize the base layouts though.
I came here tonight to ask this. It's disappointing that nobody else even seems to understand your question. After thinking about it for a couple more hours, I think I might know the answer.
Consider this example:
The red box represents a LinearLayout with vertical orientation. The green box represents another LinearLayout with horizontal orientation. I would expect the layout to proceed like this:
1) The red LinearLayout would measure the heights of green LinearLayout and the large blue widget on the bottom, then compare their weights, divide any leftover vertical space accordingly, and measure the children again. (The important thing to know here is that "measuring" a view actually sets its size.)
2) The green LinearLayout would then measure the widths of its three children, compare their weights, divide the horizontal space, and "measure" again.
The catch is that in order for the red layout to measure the height of the green layout, the green layout needs to know the height of its children.
Now, you would think that LinearLayout would be smart enough to optimize away many of its calculations. For example, there is no logical reason for the green layout to measure the width of its children when determining its own height. And if its children all have a height of fill_parent, then it shouldn't need to perform any calculations at all.
But the API doesn't allow LinearLayout to be that smart. The fundamental problem is that there is no way to measure only one dimension of a view. You can get them separately after they've been measured, but the actual measurement is done by View#onMeasure(int, int). The arguments to that method are encoded with View.MeasureSpec, and there's no way to encode "ignore this dimension." So the green LinearLayout stupidly calculates both dimensions of all its children when the red layout measures it, then repeats the entire process again when it does its own layout. The widths will not have changed the second time around, but they must still be recalculated because, again, there's no way to tell the layout or its children to measure only one dimension.
So to answer your question... no, it doesn't necessarily need to be this way, at least for many common use cases. This is a deficiency of the Android API.
If Google were to add new methods to View to measure dimensions separately, the default implementation would have to rely on onMeasure(int, int), which could be even worse for performance. But if there are any unused bits in the View.MeasureSpec encoding, then it might be possible to add an "ignore" flag that would allow future versions of LinearLayout to be better optimized.
The problem in my opinion is the measure cache. As far as I could see the cache only works if there was a layout of the view in the middle, so when you perform two consecutives measures of a child (even with the same exact measure specs) in the same "onMeasure" all the children and their sub-children are measured again. If the measure cache worked fine, the second measure should be much faster as it would take the cached values and it wouldn't cause all the children hierarchy to be measured again.
I'm prone to abusing LinearLayout, every screens there's usually three or four-level deep. Layout's design usually given size in percentages. Graphic cut to pieces and not utilizing 9-Patch. All of these resulting in me using layout_weight to represent percentages almost everywhere. Today I updated ADT and Lint has this nested weights warning everywhere. Now I'm really concern about the performance if I carry this habit into a bigger application. Is there a better way to do it without changing anything from designer's side?
If I start to get too many layers of LinearLayouts I tend to switch to a RelativeLayout at the root and most of the children only 1 layer removed from root.
9-Patch resources are very helpful also. I suggest you start to make use of those more.