DialogHost: IME Candidate Window Appears at Top-Left of Screen When Typing Full-Width Characters in TextBox

[Audela-220]

Bug explanation

When typing full-width characters (e.g., Japanese) into a TextBox displayed within a DialogHost, IME candidate window appears at the top-left corner of the screen instead of near the TextBox.
This significantly degrades the user experience.

Expected Behavior
The IME candidate window should appear properly near the TextBox being used for input.

Reproduction
This issue has been confirmed to be reproducible in the MaterialDesignXaml Demo App.

Potential Cause
This issue might be related to a known WPF problem concerning IME candidate window positioning within Popup controls, as DialogHost internally uses Popup. Popup controls do not have a clear owner window like standard Windows, which could prevent the IME from determining the correct display location.

Version

5.2.1

[corvinsz]

@Audela-220 for a quick fix on your side, you can just use the Style="{StaticResource MaterialDesignEmbeddedDialogHost}" on the DialogHost and it should work fine, since that style does not use a Popup internally:

Edit: I hope the above "fix" is applicable to your app. When switching the Dialog style to MaterialDesignEmbeddedDialogHost, the only difference (from the users perspective) is that the dialog can no longer extend beyond the dimensions of the containing window.

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From my research on the internet this is not trivial to fix, because it requires to call and position the IME popup by yourself via the Win32 IME API (ImmSetCompositionWindow).
https://stackoverflow.com/questions/69911485/windows-api-programmatically-moving-the-windows-ime-input-box-possible

[Audela-220]

@corvinsz Thank you for the quick reply! That's good to know.
However, that workaround isn't really feasible for me.
Because I'm using DialogHost specifically to display content that exceeds the parent window's bounds.

I also understand that a fundamental fix for the IME issue isn't straightforward and requires the Win32 API (ImmSetCompositionWindow).
I'll continue with the current implementation for now.

Really appreciate you looking into this and all the detailed info!