{"id":6345,"date":"2019-08-08T20:44:22","date_gmt":"2019-08-08T20:44:22","guid":{"rendered":"https:\/\/cheesecakelabs.com\/blog\/?p=6345\/"},"modified":"2022-07-01T17:15:12","modified_gmt":"2022-07-01T17:15:12","slug":"understanding-android-views-dimensions-set","status":"publish","type":"post","link":"https:\/\/cheesecakelabs.com\/blog\/understanding-android-views-dimensions-set\/","title":{"rendered":"Understanding when and how Android Views have dimensions set"},"content":{"rendered":"

I believe that almost every Android dev has at least once tried to get a View\u2019s dimension, but it returned 0, <\/span>nada<\/span><\/i>. This is a very common situation, it is one of those problems that we just Google for a solution and find a workaround that seems to work. We add it to the code without having much idea of what\u2019s going on and that\u2019s it. In this article I\u2019ll explain why this happens and why many of the most used workarounds should be avoided. In the end, I\u2019ll give you a very sweet solution about Android views.<\/span><\/p>\n

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Views dimension in Activity lifecycle <\/span><\/h1>\n

One of the very basic Android concepts that we first learn is the Activity lifecycle. We understand that the <\/span>onCreate()<\/span> callback is where the UI should be declared and configured. Having this in mind, let\u2019s say we have a View that for some reason needs a manual setup like this:<\/span><\/p>\n

myView.layoutParams.width = myView.width \/ 2<\/code><\/pre>\n
This sets <\/span>myView<\/span> width based on its own width, this means that this code should run only once. You add it inside <\/span>onCreate()<\/span> right after setting content view, run the application but it doesn\u2019t work as expected. <\/span>myView<\/span> had a width of zero and then your code just divided 0 by 2. So you think, maybe the view will be laid out in <\/span>onStart()<\/span>. You test it and again it doesn\u2019t work. Maybe <\/span>onResume()<\/span> will work? Wait… what?! <\/span>onResume<\/span> doesn\u2019t work either?! The next lifecycle step should be when the Activity is already running and you are still unable to finish the UI setup. What else can we do?<\/span><\/p>\n
\"A<\/p>\n
Ok, let\u2019s be radical and try <\/span>onWindowsFocusChanged()<\/span><\/a>. <\/span>Voil\u00e0<\/span><\/i>, it works! You are happy and can go back to work. Suddenly your app goes to background and a phone call pops up, it\u2019s your mom asking you to buy some bread on your way home. After the call ends, your app comes back to the foreground, as well as your frustration. <\/span>myView<\/span> has now half the width that it should, and you realize that <\/span>onWindowsFocusChanged()<\/span> was called again after the app came back to the foreground. <\/span><\/p>\n
\"Gif<\/p>\n
We now know that for some reason there isn\u2019t a lifecycle callback for when the activity UI is fully laid out, which is something that some stacks provide for us, such as on iOS. So the question is, when is a view fully laid out and drawn?<\/span><\/p>\n
How Android draws the UI<\/span><\/h1>\n
An Activity layout is drawn upon the view hierarchy. From the image below, you can see that this hierarchy is a tree with two different nodes – ViewGroup and View.<\/span><\/p>\n
\"View<\/p>\n
ViewGroup is also a View, but it is a layout or container that can contain many children. Examples of ViewGroups are LinearLayout and ConstraintLayout. View is any other UI component. <\/span><\/p>\n
Each View has two different types of sizes: the measured width and height, which is basically how big it wants to be, and the width and height that are the actual dimensions they have after being laid out. The desired size cannot always be provided, e.g. a view could request a width larger than its parent\u2019s width. <\/span><\/p>\n
Both measured and actual sizes are set in two steps: <\/span><\/p>\n