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Editorial Team
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Asked: 2026-05-25T19:40:43+00:00

I need to makes some changes to a ToolTip programmatically. That sounds simple enough.

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I need to makes some changes to a ToolTip programmatically. That sounds simple enough. Well, apparently not really. :/

I have a ToolTip on a WindowsFormsHost object and I make the following cast to get to the IsOpen property: 

((System.Windows.Controls.ToolTip)host.ToolTip).IsOpen = true;

This line fails during runtime with an InvalidCastException.

Unable to cast object of type ‘System.String’ to type
‘System.Windows.Controls.ToolTip’.

I don’t understand why this is failing. I must be missing some thing terribly simple as this code apparently works just fine in this example. @_@

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1 Answer

  1. Editorial Team

    ToolTip is not by accident of Type object and not ToolTip. If you set the ToolTip in XAML like this ToolTip="Test" then your ToolTip is of type String. Have a look at this. To modify your tooltip, i would suggest not using it in code directly, instead use the power of XAML and DataBinding. If you insist doing it in code, create an actual ToolTip for the property.

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