Friday, 21 September 2012

How to (start) writing a custom inspector in Unity

Unity's editor extension documentation is quite sparse, so I'm sharing some of what I did this week to help confused developers.

Here is more or less a template for starting a custom inspector script:

What we have here is an inspector for a Monobehaviour of type Trigger, as denoted by [CustomEditor(typeof(Trigger))], which should be adapted for your own objects.  Editor scripts inherit from the Editor class and have an OnEnable function, which works similarly to Start in a normal monobehaviour.

In the beginning

The first thing you'll notice is I convert target into a SerializedObject.  The reason you want to do this is explained in this video, which you'll probably want to watch anyway to learn more about editor scripting.  After that you'll probably want access to the variables in your monobehaviour.  My triggers are round, so they have a public int called radius, and I get access to it by calling FindProperty("radius") and assigning it to a SerializedProperty.

Showing stuff

Now you can access all the properties of your object, so you're going to want to show them to the user. So let's take this party to the OnInspectorGUI() function.  First of all, you're going to want to call Update() on your serialized object.  You do this because of reasons.  Seriously, I don't know what this does but apparently it's important even though nobody thought to mention it anywhere.  Next I added a label for posterity, and a property field.  PropertyField displays the default inspector control for the given property type, which in this case is an int.  Finish by calling ApplyModifiedProperties() on your object.  This applies all the changes you made, but also gives you the ability to undo and other goodies, which clear from the documentation right?. Anyway, at this point you've duplicated exactly what the default inspector view gives you, good work!  By the way, incase you actually wanted to draw the default inspector you can call DrawDefaultInspector() as well.

Showing cooler stuff

Let's make something more interesting, like a dropdown.  I gave my Triggers a priority variable, which is an int, but sometimes it's hard to remember if a low number is priority or high priority.  So instead I added a dropdown with the descriptive choices low, medium, and high.

The code looks something like this.  It the same code as before, but with an added property, a list of words to fill the dropdown and the code to draw it.  The dropdown, or "Popup", is between a horizontal layout block, as denoted by HorizontalBegin() and HorizontalEnd().  Basically all this does is put all the GUI elements between in the block next to each other.  The Popup() function is pretty straightforward, give it the current index and an array of strings to fill itself, and it returns the selected index.  When you're done, it should look something like this

So now you've gotten a taste of building a custom inspector.  Later I'll post about how to make a drag and drop area and other goodies, but if you want to get ahead you should watch this video.