Excel VSTO C＃-设置雷达图类别和轴标签的格式

Question

I'm trying to change the format of the text on a radar chart's axis and category labels, my code works for the axis font size and gives the desired output but I'm also receiving an error once the code runs on the line ax.Format.TextFrame2.TextRange.Font.Size = 7;

Error from debug:

An exception of type 'System.Runtime.InteropServices.COMException' occurred in mscorlib.dll but was not handled in user code. Additional information: Unspecified error (Exception from HRESULT: 0x80004005 (E_FAIL))

How do I change the category labels and what might be causing the error here once the action is completed?

Here's the code:

public static void FormatRadarLabels(Excel._Application xlApp)
{
    Excel.Chart chart = null;
    xlApp.ScreenUpdating = false;

    try {

        chart = xlApp.ActiveChart as Excel.Chart;

        foreach (Excel.Axis ax in chart.Axes()) {
            ax.Format.TextFrame2.TextRange.Font.Size = 7;
        }
    }
    finally {
        if (chart != null) Marshal.ReleaseComObject(chart);
        xlApp.ScreenUpdating = true;
    }

}

The method is called by a method in another class which is called by a button on an excel toolbar but I don't think the error has any issues with anything external as if I comment or removed this piece of code the rest of the formatting works fine.

Thank you for any help or suggestions offered. Please bear in mind I am relatively new (6 months experience) to C#, VSTO and Visual Studio so may not understand all technical jargon. I'm also happy to provide further information if required. :)

Answer 1

What property exactly fires an exception?

ax.Format.TextFrame2.TextRange.Font.Size = 7;

I'd suggest starting from breaking the chain of property and method calls and declaring them on separate lines. Thus, you will find what property or method exactly fires an exception.