Memory leak created by the ColumnStylesHelper

[lipchev]

Describe the bug

The DataGridColumnStylesHelperExtension is attached but never detached from the grid, leaving a memory leak with the Columns.CollectionChanged handler. This causes the whole window that is hosting the data grid to remain in memory.

Steps to reproduce

1. Replace the albums list view in the CleanWindowDemo.xaml with an equivalent data grid
2. Open and close the CleanWindowDemo

Expected behavior

When the parent is unloaded the memory is liberated

Actual behavior

The CleanWindowDemo window is retained in memory via the grid and the DataGridColumnStylesHelperExtension (see screenshot below)
Repeating the same steps with the mah:DataGridHelper.ColumnStylesHelper="{x:Null}" and the problem no longer occurs

Environment

MahApps.Metro version: v2.0.0
Windows build number: Win10 1909 [Version 10.0.18363.836]
Visual Studio: 2019 16.6.0
Target Framework: .Net Core 3.1 (v4.5.2, v4.7.2)

Screenshots

[lipchev]

Ouch, I just realized there is only one instance of the DataGridColumnStylesHelperExtension markup extension ever created.

[punker76]

@lipchev Correct, for each DataGrid. But I still can not reproduce a memory leak with this extension.

[lipchev]

The attach is called per grid, but it only overrides the private DataGrid field

[lipchev]

Cool, I tried returning a new instance in the ProvideValue and the leak is gone (even without calling detach)