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Calling c++ (dll) from c# with an LPCTSTR parameter

Thu, 15 Oct 2015 12:13:00 +0000

An example of calling a c++ dll from c#.

First, some simple c++ code.

test.h

`1`	`extern "C" __declspec(dllexport) int test(LPCTSTR szFileName);`

test.cpp

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int test(LPCTSTR szFileName) {
     return 0;
}

Next, the c# side

[DllImport("sampleLib.dll", CallingConvention = CallingConvention.Cdecl)]
private static extern int test( [MarshalAs(UnmanagedType.LPWStr)] string szFileName);

private void button2_Click(object sender, EventArgs e)
{
    string szFileName = @"c:\filename.txt";
    int result = test(ticketName);
    Debug.WriteLine("test=" + result);
}

CallingConvention = CallingConvention.Cdecl and [MarshalAs(UnmanagedType.LPWStr)] are the important parts.

The other way around, receiving a string from c++: take it as IntPtr and do this.

IntPtr ptr = test("111111");
string data = Marshal.PtrToStringAnsi(ptr);
// 꼭 해제 한다
Marshal.FreeHGlobal(data);

Saving a control to png in WPF (c#)

Thu, 15 Oct 2015 12:13:00 +0000

I was going to use System.Drawing like I did before.. turns out wpf already has this built in..

// uiPage.ren
public void DoPageToPng(string fileName)
{
    RenderTargetBitmap rtb = new RenderTargetBitmap((int)uiPage.ActualWidth, (int)uiPage.ActualHeight, 96, 96, PixelFormats.Pbgra32);
    rtb.Render(uiPage);

    PngBitmapEncoder png2 = new PngBitmapEncoder();
    png2.Frames.Add(BitmapFrame.Create(rtb));
    using (MemoryStream stream = new MemoryStream())
    {
        png2.Save(stream);
        using (System.Drawing.Image image = System.Drawing.Image.FromStream(stream))
        {
            image.Save(fileName);
        }
    }
}

Built on .NET Framework 4.5.2. Then downgraded to 4.0...

Wed, 16 Sep 2015 20:21:00 +0000

Recently I had to build a Windows app.

I heard .NET 4.5 added the new async syntax, so.. might as well, I went with 4.5.2. Oh…… it’s incredibly convenient.!!

async and await are the two important parts. Especially in UI programs, they make syncing between the background thread and the main thread easy.

Below is code that takes an id/pwd and authenticates against a server.

private async void btnLogin_Click(object sender, RoutedEventArgs e)
{
    string id = tbEmail.Text;
    string pwd = tbPassword.Password;

    SetControlEnableState(false);
    bool isSuccess = await Task.Run<bool>(() =>
    {
        try
        {
                    // 여기가 네트워크 통신을 하는 부분이다.
            _dataCore.DoLogin(id, pwd);
            return true;
        }
        catch (Exception x)
        {
            ErrorHandler.ErrorDump(x, true);
            return false;
        }
        });

    if (!isSuccess)
    {
        SetControlEnableState(true);
        return;
    }
}

As you can see, the login is handled entirely in the client event… with no separate thread synchronization..