2021-06-21_19:13:03
Editing components inside the Blueprint Editor is weird.
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Read FComponentVisualizer::NotifyPropertiesModified in ComponentVisualizer.cpp line 237 in Unreal Engine 4.25.
)
When editing a Blueprint Actor class in the Blueprint Editor there are multiple representations of the class simultaneously.
When selecting one of the Components in there are multiple representations of that as well.
The Details Panel owns one of them. That Component instance is named MyVariable_GEN_VARIABLE and does not have an owning Actor.
The Viewport owns the other. That Component instance is named MyVariable and is owned by an Actor named MyBlueprint_C_0.
I guess that in addition to these two there are also Blueprint-specific types representing the same thing, such as UBlueprint and USCSNode.
- Details Panel:
MyVariable_GEN_VARIABLEin ownernullptr. - Visualizer:
MyVariablein ownerMyBlueprint_C_0.
If you have a Component Visualizer with Hit Proxies then the Component owned by the _C_0 Actor will be provided.
If you ask ask Detail Layout Builder for the customized object then it will return the GEN_VARIABLE one without an owning Actor.
The MyVariable_GEN_VARIABLE object is the template, the object that instances of the Blueprint will be initialized from and the yellow UProperty reset button will be shown if the instance's UProperty has a value different from that on MyVariable_GEN_VARIABLE.
There can be multiple Details Panel open at the same time, but only a single Component Visualizer.
Each frame all Details Panels have their Tick function called.
If they get the Component Visualizer for their Component then they will all get the same instance even though they may be the Details Panel for different Component instances.
You can test this with the Spline Component. Create a Blueprint Actor with a Spline in it and an Empty Actor in the level also with a Spline. Select the Spline in the Empty Actor and keep an eye on the Selected Points category in the Details Panel. Then open the Blueprint in a separate window next to the main Unreal Editor window, select one of the Spline nodes and move it around. You will see the Blueprint's Spline's data in the Selected Points category of the Details Panel in the main Unreal Editor window. All other categories will display the state of the Empty Actor Spline, but that one Category will display the state of the Blueprint-owned Spline. That's gonna lead to confusion.
If using the click-to-track approach in the Component Visualizer, like the Spline does, then when the Details Panel is first opened nothing will have been clicked yet so the Component Visualizer will have a null Component.
It may be possible to track multiple selected Components in the Component Visualizer and do some kind of look-up in the Detail Panel's Tick function so that the correct Component is always used.
Not sure how one would know that it's safe to remove stuff from that map/cache.
When a UProperty on a Blueprint instance is edited in the Details Panel the Actor is serialized, Component Instance Data gathered, all Components destroyed, new Components created, the Construction Script run, the serialization deserialized, and the gathered Component Instance Data applied. This process must be considered everywhere you are modifying Components, or parts of Components, that may be part of a Blueprint.
During Blueprint Reconstruction, when Components are destroyed and recreated, new Details Panels are also created.
These new Details Panel are given new Property Handles pointing to the new objects.
A Details Customization may contain callbacks, for example for handling a button click or a new selection in a combo box.
The Details Panels for the destroyed Components live on for a bit and the callbacks associated with them may be called during this time.
We call these Zombie Details Panels.
That means that in the callbacks for a Details Panel created for some object we may not rely on the object still existing.
We can detect this by inspecting our Property Handle, which will be cleared (GetNumPerObjectValues returns 0) during the Blueprint Reconstruction.
In particular, calling Set Value on an Property Handle when the Handle points to a UProperty on a Component in a Blueprint instance will cause the Component to be destroyed and the very Property Handle we called Set Value on to become cleared.
[[2020-08-06_18:48:41]] Component visualizer
[[2021-06-16_10:48:57]] Property Customization