wpf radgridview How to get vertical offset of GridViewRow? - wpf

Question

I have row index of target GridViewRow, and ScrollChanged handler callback of GridViewScrollViewer inside RadGridView. I want to get vertical offset of target row in viewport, while scrolling, if that row leaves viewport from top, return 0; if leaves from bottom, return ActualHeight of RadGridView; else, get a value same as Top offest of target row and viewport.
Here is function to get vertival offset, it will be incorrect after scrollbar moved:
//const int indicator_size = 3;
//RadGridView grid;
Func rowIndicatorOffset = (rowIndex) =>
{
double offset = (rowIndex + 1.5) * this.grid.RowHeight;
if (offset > this.grid.ActualHeight)
{
return this.grid.ActualHeight - indicator_size;
}
return offset;
};
When change vertical scroll bar offset, I want that indicator(red one in the picture above) keep same Y position with target row:
//System.Windows.Controls.ScrollChangedEventArgs offsetValues (from ScrollChanged event)
double fixRatio = (this.grid.ActualHeight - this.offsetValues.VerticalOffset) / this.grid.ActualHeight;
double offset = (rowIndex + 1.5) * this.grid.RowHeight * fixRatio;
the code above works not well as expected apparently, so what's the answer?

Answer 1

I got it wrong about Viewport, the diagram below may figure it out.
diagram
//const int indicator_size = 3;
//RadGridView grid;
Func<int, double> rowIndicatorOffset = (rowIndex) =>
{
double targetOffset = (rowIndex + 1.5) * this.grid.RowHeight;
double viewportOffset = this.offsetValues.VerticalOffset;
double offset = targetOffset - viewportOffset;
if (offset > this.grid.ActualHeight)
{
return this.grid.ActualHeight - indicator_size;
}
else if (offset < 0)
{
return 0;
}
else
{
return offset;
}
};