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POView.post(), and when Runnables are executed
 

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    <p>My original problem was needing to know the height and width of my root <code>View</code> so that I could make programmatic layout changes. For my purposes, I don't necessarily need to determine this information during <code>onCreate()</code>; it's quite sufficient for me to programmatically add my child <code>View</code>s after layout of the root has completed, so therefore I'm happy to use <code>onWindowFocusChanged()</code> as a hook to determine when calling the root <code>View</code>'s <code>getWidth()</code> and <code>getHeight()</code> will return valid results. </p> <p>However, I see quite a few people have asked how to determine the root <code>View</code>'s size during <code>onCreate()</code>. I'm guessing people want to do this for better user experience - perhaps so that users don't see the layout being built in stages (if anyone can clarify the reasons, I'd appreciate it). Now, the answer I have commonly seen given to this, such as the one <a href="https://stackoverflow.com/questions/3602026/linearlayout-height-in-oncreate-is-0">here</a>, is to post a <code>Runnable</code> to the root <code>View</code> within <code>onCreate()</code>. Inside that <code>Runnable</code> we perform the <code>getWidth()</code>, etc. The reason why this works is because, apparently, <code>Runnable</code> objects posted to a <code>View</code> are executed when the <code>View</code> has layout and / or is attached to the window. </p> <p>This brings me to my question. In the API documentation for <code>View</code>, it doesn't seem to describe this behavior. So, can anyone tell me where it is defined and documented? Or, is it a matter of inspecting the source? Is it an absolutely and rigidly defined feature that <code>Runnables</code> will stay in a <code>View</code>'s queue and only be handled at a certain point after the layout process?</p> <p><strong>Further clarification:</strong> On reading Kerry's answer and thinking it over a bit more, my basic question can be clarified as follows: In the answer given <a href="https://stackoverflow.com/questions/3602026/linearlayout-height-in-oncreate-is-0">here</a> and also in this <a href="http://www.codeproject.com/Tips/313848/Get-actual-screen-size-for-the-application-layout" rel="nofollow noreferrer">CodeProject entry</a>, I understand that we get around the problem of the root <code>View's</code> dimensions not being available during the <code>onCreate()</code> by posting a <code>Runnable</code> to the <code>View</code>. As Kerry points out, the guarantee is that this message <code>Runnable</code> cannot be executed until <code>onCreate()</code> has executed. I understand that layout occurs some point after <code>onCreate</code>, but I still can't grasp at the moment why this <code>Runnable</code> should execute when the <code>View</code>'s dimensions are known. </p>
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    1. COJust further to your additional info. The examples you gave in CodeProject in my opinion not so good. I think the post() method should be called in the onSizeChanged() method of the child view. They way they have done it I'm not 100% convinced even the Root views size will be known (if calling from child.onCreate()). Calling from child.onSizeChanged() the root view MUST have size for it to allow the child to be drawn. Consequently that's why I say call it from the onSizeChanged() method.
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    2. COI agree, and for my purposes I will take your advice and use `onSizeChanged()`. But, the fact that it is Romain Guy who recommended the post() method (http://stackoverflow.com/questions/3602026/linearlayout-height-in-oncreate-is-0) makes me believe that there is something well defined in the APIs that guarantees that the `View` will process the `Runnable` only when it has layout. I guess this is all academic really, but I would like a further understanding as to why that is. I posted a comment to Romain.
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