Extend Content Block Media Upload Logic: Pre-selecting a Default LIbrary

This blog post exposes a way to extend the default logic of the Image/Video/Document upload of Sitefinity's content blocks. Lately there have been some requests for different users with different permissions to have a predefined library selected when an upload is made. The case this blog post will cover is to select the first library the current user has permissions to and upload all content there.

 In order for us to be able to add additional logic to the dialog loaded by the Content Block, we will need to override three dialogs - MediaContentManagerDialog, SingleMediaContentSelectorView and finally, MediaContentManagerDialog. 

First off, the primary dialog loaded is the MediaContentManagerDialog. This is the one we need to replace with a custom one in the Unity Container through ObjectFactory. First we create a class that inherits from the MediaContentManagerDialog one. The one I created is called CustomMediaContentManagerDialog and is registered as per this documentation article in the Global.asax file:

Once done we need to override the base template of the MediaContentManagerDialog along with its script descriptors and its SelectorView.LayoutTemplatePath:

Notice that we need a custom template for both the MediaContentManagerDialog and the SingleMediaContentSelectorView. You can find both ascx files below.
CustomMediaContentManagerDialog.ascx: 

And 
CustomSingleMediaContentItemView.ascx:

Pay attention to the highlighted parts. They are the replacement controls needed. Also, each template includes a register directive that adds the SitefinityWebApp namespace and therefore resolves the controls needed.

Next up we need to override the SingleMediaContentItemView such that it uses our own control for its imageSelector. Below is the code of my CustomSingleMediaContentItemView class.
Finally we get to the dialog we need in order to set the document library - the SingleMediaContentItemDialog. All additional logic needs to be placed here. The controls we were overriding so far were in order to get to this dialog. What we need is the default template (no modifications needed) of the SingleMediaContentItemDialog:
Next up we need to override the logic of its InitializeControls method along with passing some script descriptors in order to avoid JavaScript errors. The methodology I followed here is as follows - after the dialog initializes its base methods, I take the current user identity and its role, I get an instance of the LibrariesManager and get all libraries, after which I check if the current user is in the specified role and based on the permissions he/she has for the libraries, make the upload target the specific library the user has permissions to. The code queries the Editors role, but can easily be modified:
Note that the example is relevant for Documents only. If you want to do the same for videos and images, you will need to add an else and finally clause to the if statements and check for the Dialog mode. It takes three parameters - Video,Document and Image (also NotSet but we do not need this here). In other words something like the following should suffice for images:

And also you will need to get all albums, not DocumentLibraries:

 Here is a sample picture for better understanding:

Before:

After:

You can find the complete code sample in in GitHub.