Add new obscure qt blog post

content/blog/obscure-qt1.md

@@ -0,0 +1,74 @@
+---
+title: "Obscure Qt: Default choices for DelegateChooser"
+date: 2023-04-19
+draft: false
+tags:
+- Qt
+---
+
+I decided to start a short series of describing weird, obscure Qt behavior! Because of my new job, I'm working with Qt even more than I did before. As I'm finding new and undocumented behavior, I feel that it's too useful to be posted on something like Mastodon and then forgotten.
+
+A really useful component is the [DelegateChooser](https://doc.qt.io/qt-6/qml-qt-labs-qmlmodels-delegatechooser.html). Say you are building a chat application, and you need to support different types of messages (a regular text message, an image, a location and so on). In order to accomplish this in Qt Quick is to do something like this:
+
+```qml
+DelegateChooser {
+	role: "type"
+	DelegateChoice {
+		roleValue: "message"
+		
+		Label {
+			required property string message
+		
+			text: message
+		}
+	}
+	
+	DelegateChoice {
+		roleValue: "image"
+		
+		Image {
+			required property string url
+			
+			source: url
+		}
+	}
+	
+	...
+}
+```
+
+At runtime, Qt Quick will use `role` and check it against every one of the [DelegateChoice](https://doc.qt.io/qt-6/qml-qt-labs-qmlmodels-delegatechoice.html)'s `roleValue`. When it finds a match, it'll choose that component. Really useful stuff!
+
+But today I encountered a different case, where I had a bunch of values in my role but not all of them had to be specialized. In most cases I had one component that's generalized for most of them, but only one or two that needed a different component. Curiously, the Qt documentation does not say how to accomplish something like this:
+
+```cpp
+switch(type) {
+	case SpecialType:
+		return SomeComponent{};
+	default:
+		return DefaultComponent();
+}
+
+```
+
+After doing some digging I found a Qt mailing list from a couple years ago, with some developers discussing what to do about "default" cases for `DelegateChooser`. Someone suggested leaving the `roleValue` empty as a way to support that. And it seems to work in Qt today, albeit undocumented:
+
+```qml
+DelegateChooser {
+	role: "type"
+	DelegateChoice {
+		roleValue: "specialType"
+		
+		Label {		
+			text: "I'm a special type!"
+		}
+	}
+	
+	// This is the default choice!
+	DelegateChoice {		
+		Label {
+			text: "I'm everyone else..."
+		}
+	}
+}
+```