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Fixed in 2020.2.X

Fixed in 2019.3.X, 2020.1.X



Found in






Issue ID




Dragging a UI Prefab to the Scene view incorrectly shows it in the Hierarchy and an ArgumentOutOfRangeException is thrown

Scene Hierarchy


Steps to reproduce:
1. Create a UI slider
2. Create a Prefab of it.
3. Drag the Prefab Asset over the Scene View (without letting go) then over the Hierarchy

Expected result: No Exception is thrown and Prefab is not added to the Hierarchy
Actual result: ArgumentOutOfRangeException is thrown and Prefab is added to the Hierarchy

Reproduced in: 2019.1.0b7, 2019.3.4f1, 2020.1.0a26, 2020.2.0a1
Not reproducible in: 2017.4.37f1, 2018.4.18f1, 2019.1.0b6

- The issue is reproducible with the following UI objects: Slider, Scrollbar and Scrollview
- You can make the error appear multiple times by dragging back and forth over Scene view and Hierarchy repeatedly
- Also note that while dragging over the Scene view (without letting go) a temporary instance of the Prefab appears in the Hierarchy, which should not happen. Perhaps some code that hides temporary objects used for Scene view dragging preview is not being run for some reason.

Bisection identified this PR as causing the regression:
Specifically the revision:

  1. Resolution Note (fix version 2020.2):

    Fixed in 2020.2.0a9

  2. Resolution Note (fix version 2020.1):

    Fixed in 2020.1.0b9

  3. Resolution Note (fix version 2019.3):

    Fixed in 2019.3.15f1

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