Code Snippets

Passing an enumerated list to a PropertyBag for a PropertyGrid

I've been using the PropertyBag class to build up a set of properties to pass to a PropertyGrid control. However, it required passing a type for each enum to list the strings and that meant creating a StringTypeConverter derived class for each enum - which is a problem if you will have N enums.

Download PropertyBag.cs is derived from the original but includes a property constructor that takes an array of string rather than a type and displays those strings as the enum choices. I made a couple of other small edits to the original code but otherwise it's the original PropertyBag.

Answer

To set a default property you do it like for any other property - you just do:
PropertyTable props = ...
props["name"] = value;

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Get screen DPI in .NET

You would think that this exists in .NET (like maybe the Screen class) but there is aparently no way in .NET to get the DPI of the screen. So here it is using p/invoke.

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public class NativeMethods
{
  [DllImport("gdi32.dll", EntryPoint = "CreateDC", CharSet = CharSet.Auto, SetLastError = true)]
  private static extern IntPtr CreateDC(string lpszDriver, string lpszDeviceName, string lpszOutput, IntPtr devMode);

  [DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]
  static extern bool DeleteDC(IntPtr hdc);

  [DllImport("gdi32.dll", SetLastError = true)]
  private static extern Int32 GetDeviceCaps(IntPtr hdc, Int32 capindex);
  private const int LOGPIXELSX = 88;

  private static int _dpi = -1;
  public static int DPI
  {
   get
   {
    if (_dpi != -1)
     return _dpi;

    _dpi = 96;
    try
    {
     IntPtr hdc = CreateDC("DISPLAY", null, null, IntPtr.Zero);
     if (hdc != IntPtr.Zero)
     {
      _dpi = GetDeviceCaps(hdc, LOGPIXELSX);
      if (_dpi == 0)
       _dpi = 96;
      DeleteDC(hdc);
     }
    }
    catch (Exception)
    {
    }

    return _dpi;
   }
  }
}

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