Skip to main content

Measuring UI freeze in WPF applications with Reactive Extensions

Making sure an application doesn't freeze the UI is probably one of the most important concerns when building an application. UI freeze can be broken down into two categories,firstly long running background tasks and secondly the rendering of UI elements (controls) to the screen.

The second situation is what interests me with this post, usually UI based applications will dedicate a single thread to rendering the UI (dispatcher). This thread in theory can become overloaded with work and therefore the UI  becomes unresponsive to the user until the work is completed - the app freezes. Measuring this freeze on the dispatcher is useful in diagnosing the problems of rendering large amounts of data in a short time frame, e.g. like trying to render a large number of rows in a grid.

How can I measure this freeze?

You can do this easily with a couple of Rx methods:
Loading ....
The key is making sure they execute on the dispatcher thread. This ensures that when the dispatcher is overloaded they will not fire at the expected interval and therefore the interval between current & previous will be large enough for the stream to pump. This is then used at startup:
Loading ....
The following simple UI simulates the affect of overloading the dispatcher thread, you can see I've routed the button click through to a method which does a thread sleep on the dispatcher thread:
Loading ....
When the button is clicked serveral times I get the following output:

Comments

Popular posts from this blog

Showing a message box from a ViewModel in MVVM

I was doing a code review with a client last week for a WPF app using MVVM and they asked ' How can I show a message from the ViewModel? '. What follows is how I would (and have) solved the problem in the past. When I hear the words ' show a message... ' I instantly think you mean show a transient modal message box that requires the user input before continuing ' with something else ' - once the user has interacted with the message box it will disappear. The following solution only applies to this scenario. The first solution is the easiest but is very wrong from a separation perspective. It violates the ideas behind the Model-View-Controller pattern because it places View concerns inside the ViewModel - the ViewModel now knows about the type of the View and specifically it knows how to show a message box window: The second approach addresses this concern by introducing the idea of messaging\events between the ViewModel and the View. In the example below

Implementing a busy indicator using a visual overlay in MVVM

This is a technique we use at work to lock the UI whilst some long running process is happening - preventing the user clicking on stuff whilst it's retrieving or rendering data. Now we could have done this by launching a child dialog window but that feels rather out of date and clumsy, we wanted a more modern pattern similar to the way <div> overlays are done on the web. Imagine we have the following simple WPF app and when 'Click' is pressed a busy waiting overlay is shown for the duration entered into the text box. What I'm interested in here is not the actual UI element of the busy indicator but how I go about getting this to show & hide from when using MVVM. The actual UI elements are the standard Busy Indicator coming from the WPF Toolkit : The XAML behind this window is very simple, the important part is the ViewHost. As you can see the ViewHost uses a ContentPresenter element which is bound to the view model, IMainViewModel, it contains 3 child v

Custom AuthorizationHandler for SignalR Hubs

How to implement IAuthorizationRequirement for SignalR in Asp.Net Core v5.0 Been battling this for a couple of days, and eventually ended up raising an issue on Asp.Net Core gitHub  to find the answer. Wanting to do some custom authorization on a SignalR Hub when the client makes a connection (Hub is created) and when an endpoint (Hub method) is called:  I was assuming I could use the same Policy for both class & method attributes, but it ain't so - not because you can't, because you need the signatures to be different. Method implementation has a resource type of HubInnovationContext: I assumed class implementation would have a resource type of HubConnectionContext - client connects etc... This isn't the case, it's infact of type DefaultHttpContext . For me I don't even need that, it can be removed completely  from the inheritence signature and override implementation. Only other thing to note, and this could be a biggy, is the ordering of the statements in th