NSTableView binding with MvvmCross

Although Mac support in MvvmCross is in its infancy a lot can be accomplished by following the patterns used for iOS. This post assumes you can get the necessary plumbing working for a basic Xamarin.Mac application using MvvmCross. Most of the setup required for a Mac app can be copied from the iOS code but its beyond the scope of this post.

A NSTableViewSource is what the NSTableView uses to source its data. This is what we want to bind. We want to be able to do the following in our binding code:


This is a standard MvvmCross "Fluent" binding. See Stuarts excellent binding documentation for more information. To achieve this I have created bindable versions of NSTableViewSource, NSTableColumn and NSTableCellView. My code uses a "Cs" prefix instead of NS for the bindable versions. Of course once  (if) this code makes its way back into MvvmCross it will use the standard Mvx naming convention.

One of the big differences between the NSTableView and the UITableView is that the former has a concept of columns. What we want is to be able to specify a binding expression for each column we require. We use the editor in Xcode to do this. In the example below we have setup our NSTableView with a few columns. Notice how the binding expression for the "Process Name" column is specified as a  "User Defined Runtime Attribute" in the inspector.

"Title" is a property in CsTableCellView that simply sets the default NSTextField. Description is a property on my model class that is part of the IEnumerable in my view model.To setup a view as above follow the following steps:

1. Use a regular NSTableView.
2. Add the columns you require and change the Custom Class to CsTableColumn as below
   
3. Set the bindingText in the "User Defined Runtime Attribute" as mentioned earlier. 

If your model class implements INotifyPropertyChanged any changes to a property will reflect automatically in the column that binds the property.

The code is currently sitting in gists until I get a chance to put it somewhere permanent.

CsTableViewSource

CsTableColumn

CsTableCellView

Updating my mobile apps for Async

Xamarin recently announced support for Async in the form of an Alpha release. Time to update some code to take advantage.

Above is the change made in my service class that log's a user in. The LoginSession class was already returning a Task. I removed the ugly ContinueWith and the 2 delegates passed in. Now I just return the Task.

In my LoginViewModel I can make the changes above. Much cleaner. Note how the lambda passed to the RelayCommand is marked as Async. This is the magic that allows me to wait on the CsService.Login call. Once the Login completes I can continue where I left off in the UI thread and close the login dialog or handle any exceptions. Both the LoginComplete and LoginFailed methods are completely removed and now handled in the same order you would expect if there was no need to wait for the login to go out and make a network call (which takes time).

If you just getting into async I can recommend watching the video series by Lucian Wischik Three Essential Tips for Async

IOC Container

My objective here was to create a lightweight container using some of the newer .NET classes available. Requirements included thread safety and lazy loading.

This is more an implementation of the service locator pattern and definitely not a fully kitted IOC container as the name suggests. For someone who requires simple service registration and location from multiple threads with the added benefit of lazy loading this may be of some use.

Example Usage

Lets say you have an application consisting of a core project that contains code that you intend to reuse (for instance a portable class library) and a platform specific project that contains your UI. The UI project would register the Rope as the IPullable implementation (typically at startup). Now your core code can locate an implementation of IPullable whenever it needs it. When you port your project to another platform you can register a different implementation of IPullable (ElasticBand for example). Your core code remains unchanged and is non the wiser that its now pulling an elastic band instead to a rope.