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Asked: 2026-05-10T21:40:21+00:00

I have a control in Silverlight 2 that changes state during the application. When

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I have a control in Silverlight 2 that changes state during the application. When its state changes, I want to update the tooltip that goes with it.

I’m using the ToolTipService:

ToolTipService.SetToolTip(ent.LayoutRoot, 'FooBar');

which works fine the first time I set a tooltip, but fails the second time time around I get:

'Object reference not set to an instance of an object' from somewhere inside Silverlight where I can’t get a useful stack trace / break point.

Trawling the net pops up a few similar problems but no solutions.

Can anyone shed some light on this?

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1 Answer

  1. Found the problem – it looks like you can’t set a ToolTip after the control is created. So now, I set the ToolTip in the controls constructor, then when it needs updating, the call to SetToolTop() works just fine.

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