Exception when using FolderBrowserDialog

user_864027 0
Viewed 34979

I'm getting the following Exception when trying to use FolderBrowserDialog: System.Threading.ThreadStateException: Current thread must be set to single thread apartment (STA) mode before OLE calls can be made. Ensure that your Main function has STAThreadAttribute marked on it. This exception is only raised if a debugger is attached to the process.

I have Googled this problem extensively and the solutions that everybody suggests seem to be to put [STAThreadAttribute] above the Main method, to delete all dll's from the Debug folder, or to use the Invoke method. I have tried all of these, and I still get the same exception.

Here's the code:

public partial class Form1 : Form
{
    public event EventHandler ChooseLocationHandler = null;

    public string DestFolder
    {
        set { textBox1.Text = value; }
        get { return textBox1.Text; }
    }

    public Form1()
    {
        InitializeComponent();
    }

    private void ChooseLocationButton_Click(object sender, EventArgs e)
    {
        if (ChooseLocationHandler != null)
            ChooseLocationHandler(this, e);
    }
}

And in my presenter is the following:

public partial class Presenter
{
    Form1 myForm;
    public Presenter()
    {
        myForm = new Form1();
        myForm.ChooseLocationHandler += ChooseLocationHandler;
        myForm.Show();
    }

    public void ChooseLocationHandler(object obj, EventArgs e)
    {
        Form1 sender = (Form1)obj;

        FolderBrowserDialog fbd = new FolderBrowserDialog();
        fbd.RootFolder = System.Environment.SpecialFolder.MyComputer;
        fbd.ShowNewFolderButton = true;
        if (fbd.ShowDialog() == DialogResult.Cancel)
            return;

        sender.DestFolder = fbd.SelectedPath;
    }
}

I'm getting the Exception on fbd.ShowDialog().

folderbrowserdialog multithreading exception c#
7 Answers

As simple as the below : 

using System.Windows.Forms;
namespace fileConverterBaset64
{
    class Program
    {
        [STAThread]
        static void Main(string[] args)

Add the command [STAThread] before your main method. That's it, it would work.

user_118191040

I had the same issue with ASP.NET MVC project. When I export my crystal report to some format it shows me the error. What I have done is replace

This:

            SaveFileDialog browser = new SaveFileDialog();
            string fileName = "";

            browser.Filter = "Pdf|*.pdf|Txt|.txt";

            if (browser.ShowDialog() == DialogResult.OK)
            {
                ExportFormatType formatType = ExportFormatType.NoFormat;
                switch (browser.FilterIndex)
                {
                    case 2:
                        formatType = ExportFormatType.WordForWindows;
                        break;
                    case 1:
                        formatType = ExportFormatType.PortableDocFormat;
                        break;
                }

                fileName = browser.FileName;
                crReportDocument.ExportToDisk(formatType, fileName);

Into:

Thread thread = new Thread((ThreadStart)(() =>
            {
                SaveFileDialog browser = new SaveFileDialog();
                string fileName = "";

                browser.Filter = "Pdf|*.pdf|Txt|.txt";

                if (browser.ShowDialog() == DialogResult.OK)
                {
                    ExportFormatType formatType = ExportFormatType.NoFormat;
                    switch (browser.FilterIndex)
                    {
                        case 2:
                            formatType = ExportFormatType.WordForWindows;
                            break;
                        case 1:
                            formatType = ExportFormatType.PortableDocFormat;
                            break;
                    }

                    fileName = browser.FileName;
                    crReportDocument.ExportToDisk(formatType, fileName);
                }
            }));

            thread.SetApartmentState(ApartmentState.STA);
            thread.Start();
            thread.Join();
user_81940890

I Had This Same Issue, I Remove 3 Un-Used Dll's And it Fixed... Thank's So Much!

user_139103160

Now, check all dll in Reference and delete dll not use.

That was unbelievable. I could have never imagined those dll's are causing this problem.

user_105900350
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