wpf scrollviewer and sizechanged event question

Programmer Question

Can anyone explain to me the relationship between scrollviewer and SizeChanged event? Whenever I put a scrollViewer around a grid, numerous SizeChanged event gets fired. What is the relationship between the two? Thanks a lot.

EDIT:

From mdm20's comment, I noticed that the ActualWidth and ActualHeight of the grid increases continuously if I wrap the grid around a ScrollViewer. Can anyone explain why this is the case? Do I need to have hard values for the width and height of the grid?

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