How To Get And Set Variables From Unknown Class Via Reflection?

Unity Engine
1

I’m trying to automate the process of drawing node GUI. Here are my (desired) steps.

I want to get a list of variables from a class.

I want to loop through each variable and get its type. (is it an int, float, or something else?)

Based on the variable’s type, I want to call a GUI function to display and set the variable’s value.
(If it’s an int, I’d call the IntField method and pass in the variable’s value while setting its value to whatever the GUI function returns)

Here’s my current code. I have no idea what is triggering the (Null Reference) errors. Each frame, the chance of getting an error is hit or miss. If I pause the game and play it frame by frame, I don’t always get a new error.

Here’s my code:

/// <summary>
/// Draws a given field.
/// </summary>
/// <param name="field"></param>
static void DrawNodeField (NodeBase node, FieldInfo fieldInfo)
{
    Type fieldType = fieldInfo.FieldType;
    object fieldValue = fieldInfo.GetValue(node);

    if (fieldValue != null && fieldInfo != null && fieldType != null)
    {
        if (fieldValue is int)
            // The error points the the line below this comment
            fieldInfo.SetValue((int)fieldValue, EditorGUILayout.IntField(fieldInfo.Name, (int)fieldValue));
        else if (fieldValue is float)
            fieldInfo.SetValue((int)fieldValue, EditorGUILayout.FloatField(fieldInfo.Name, (float)fieldValue));
        else if (fieldValue is PlacementType)
            fieldInfo.SetValue((int)fieldValue, EditorGUILayout.EnumPopup(fieldInfo.Name, (PlacementType)fieldValue));
    }
    else
        Debug.Log("FieldValue of " + fieldInfo.Name + " is null.");
}

And here’s the error:

NullReferenceException: Object reference not set to an instance of an object
UnityEngine.GUILayoutUtility.DoGetRect (Single minWidth, Single maxWidth, Single minHeight, Single maxHeight, UnityEngine.GUIStyle style, UnityEngine.GUILayoutOption[ ] options) (at C:/buildslave/unity/build/Runtime/IMGUI/Managed/GUILayoutUtility.cs:374)
UnityEngine.GUILayoutUtility.GetRect (Single minWidth, Single maxWidth, Single minHeight, Single maxHeight, UnityEngine.GUIStyle style, UnityEngine.GUILayoutOption[ ] options) (at C:/buildslave/unity/build/Runtime/IMGUI/Managed/GUILayoutUtility.cs:371)
UnityEditor.EditorGUILayout.GetControlRect (Boolean hasLabel, Single height, UnityEngine.GUIStyle style, UnityEngine.GUILayoutOption[ ] options) (at C:/buildslave/unity/build/Editor/Mono/EditorGUI.cs:6857)
UnityEditor.EditorGUILayout.IntField (System.String label, Int32 value, UnityEngine.GUIStyle style, UnityEngine.GUILayoutOption[ ] options) (at C:/buildslave/unity/build/Editor/Mono/EditorGUI.cs:5548)
UnityEditor.EditorGUILayout.IntField (System.String label, Int32 value, UnityEngine.GUILayoutOption[ ] options) (at C:/buildslave/unity/build/Editor/Mono/EditorGUI.cs:5542)
Vexus.NodeUIUtilities.DrawNodeField (Vexus.NodeBase node, System.Reflection.FieldInfo fieldInfo) (at Assets/Vexus 2/Scripts/Data/Utilities/NodeUIUtilities.cs:61)
Vexus.NodeUIUtilities.DrawNodeUI (Vexus.NodeBase node) (at Assets/Vexus 2/Scripts/Data/Utilities/NodeUIUtilities.cs:20)
Vexus.NodeGroup.UpdateNodeGroup () (at Assets/Vexus 2/Scripts/Data/NodeGroup.cs:69)
VexusFlowTest.Update () (at Assets/Vexus 2/Scripts/Runtime/VexusFlowTest.cs:26)

2

your are not using SetValue right.
your object should be the instance of the class you are setting the field’s value of.

3

Ah, thank you!

4

The two arguments for the method are “obj” and “value”. Instead of passing it “(int)fieldValue” I’m passing it “node”, which is the object that holds the variable I want to change. Am I changing the wrong argument or passing the wrong object? I’m still getting the same error.

5

Actually I think I figured out what the new problem is. I was wrong in saying that I was getting the same error, the new one is responding to my UI calls. I’m just calling them out of nowhere so Unity can’t find any rects to draw my GUI on.