Auto ToolTip on TextBlock trimming

Question

I have tried everything,

solution1: https://siderite.dev/blog/determining-if-textblock-has-been.html

solution2: http://blog.scottlogic.com/2011/01/31/automatically-showing-tooltips-on-a-trimmed-textblock-silverlight-wpf.html

My solution:

<TextBlock.ToolTip> 
    <MultiBinding Converter="{StaticResource ToolTipVisibilityWhenTextTrimmedConverter}">                                 
       <Binding ElementName="mytextblock" Path="Text"/>
       <Binding ElementName="mytextblock"/>
       <Binding ElementName="mytextblock" Path="MaxWidth"/>
    </MultiBinding>
</TextBlock.ToolTip>

and

public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
{
    var text = values[0];
    TextBlock tb = (TextBlock)values[1];
    var maxwidth = values[2];
    var result = CommonMethods.MeasureString(tb);
    bool isTextTrimmed = result.Width > (double)maxwidth;
    var retval = (isTextTrimmed) ? text : null;

    return retval;
}

But still when the TextBlock width is very close to get trimmed the ToolTip is shown. Sometimes when the last 2 characters are trimmed the ToolTip is not shown.

Any suggestions?