Clipboard.GetText returns null (empty string)

Question

My clipboard is populated with text, but when I run

string clipboardData = Clipboard.GetText(System.Windows.Forms.TextDataFormat.Text);

I get back an empty string. I've toyed with various forms of the call including:

string clipboardData = Clipboard.GetText();
string clipboardData = Clipboard.GetText(System.Windows.Forms.TextDataFormat.UnicodeText);

But with the same result.

Am I missing something obvious?

Is the data that is on the clipboard "text" and not graphic, audio or other? — JMD, Feb 06 '09 at 01:07
Null is very different from the empty string. I'm not sure why "null" is part of your question. It does nothing but add confusion and misinformation. — JoelFan, Oct 02 '20 at 18:59

score 62 · Accepted Answer · edited May 23 '17 at 10:31

62

You can only access the clipboard from an STA thread. Rick Brewster ran into this with some refactoring of the regular Edit->Paste command, in Paint.NET.

Code:

IDataObject idat = null;
Exception threadEx = null;
Thread staThread = new Thread(
    delegate ()
    {
        try
        {
            idat = Clipboard.GetDataObject();
        }

        catch (Exception ex) 
        {
            threadEx = ex;            
        }
    });
staThread.SetApartmentState(ApartmentState.STA);
staThread.Start();
staThread.Join();
// at this point either you have clipboard data or an exception

Code is from Rick. http://forums.getpaint.net/index.php?/topic/13712-/page__view__findpost__p__226140

Update: Jason Heine made a good point of adding () after delegate to fix the ambiguous method error.

edited May 23 '17 at 10:31

Community

1
1

answered Feb 06 '09 at 01:06

BoltBait

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9
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5

not sure about other frameworks, but in .net 4.0 delegate needs to have () after it, otherwise you get an ambiguous method error. – CodeLikeBeaker Aug 09 '11 at 17:08
Should we add some locking ? – Toto Dec 30 '14 at 16:24
Good answer, although in my case it was just that I had a WinForms where I had removed the [STAThread] attribute on Main, so I just had to put it back. – Wade Hatler Jun 29 '16 at 16:11
Hello, I find it that sometimes the clipboard content is not immediately available after staThread.Join() returns. e.g if I try to use idat I get an old value or null etc; However, if I add a 1 second sleep before trying to access the vairable it works. Any suggestions why this might be the case? Shall I just raise a new question? I think it is relevant here if the answer means we need a sleep before accessing the variable for a reliable read. – Ali Rad Jul 26 '18 at 15:44

score 43 · Answer 2 · edited Jun 17 '22 at 08:32

43

Honestly, I don't know what a STA thread is, but in simple projects it might solve the problem to add [STAThread] right before the Main method:

[STAThread]
static void Main(string[] args)
{ (...)

It works for me, so I don't question the method ;)

Further information about the [STAThread] decorator is on blog post Why is STAThread required?.

edited Jun 17 '22 at 08:32

Glorfindel

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answered Apr 06 '10 at 16:06

Danilo Bargen

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15
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Perfect for a quick console app. – Grant Nov 16 '13 at 21:57

score 11 · Answer 3 · edited Feb 01 '21 at 08:17

I have written this class, it works, and do the same thing and can be easily improved just adding the method who you need

    Private Class ClipboardAsync

    Private _GetText As String
    Private Sub _thGetText(ByVal format As Object)
        Try
            If format Is Nothing Then
                _GetText = Clipboard.GetText()
            Else
                _GetText = Clipboard.GetText(DirectCast(format, TextDataFormat))
            End If

        Catch ex As Exception
            _GetText = String.Empty
        End Try
    End Sub
    Public Function GetText() As String
        Dim instance As New ClipboardAsync
        Dim staThread As New Thread(AddressOf instance._thGetText)
        staThread.SetApartmentState(ApartmentState.STA)
        staThread.Start()
        staThread.Join()
        Return instance._GetText
    End Function
    Public Function GetText(ByVal format As TextDataFormat) As String
        Dim instance As New ClipboardAsync
        Dim staThread As New Thread(AddressOf instance._thGetText)
        staThread.SetApartmentState(ApartmentState.STA)
        staThread.Start(format)
        staThread.Join()
        Return instance._GetText
    End Function

    Private _ContainsText As Boolean
    Private Sub _thContainsText(ByVal format As Object)
        Try
            If format Is Nothing Then
                _ContainsText = Clipboard.ContainsText()
            Else
                _ContainsText = Clipboard.ContainsText(DirectCast(format, TextDataFormat))
            End If
        Catch ex As Exception
            _ContainsText = False
        End Try
    End Sub
    Public Function ContainsText() As Boolean
        Dim instance As New ClipboardAsync
        Dim staThread As New Thread(AddressOf instance._thContainsFileDropList)
        staThread.SetApartmentState(ApartmentState.STA)
        staThread.Start()
        staThread.Join()
        Return instance._ContainsText
    End Function
    Public Function ContainsText(ByVal format As Object) As Boolean
        Dim instance As New ClipboardAsync
        Dim staThread As New Thread(AddressOf instance._thContainsFileDropList)
        staThread.SetApartmentState(ApartmentState.STA)
        staThread.Start(format)
        staThread.Join()
        Return instance._ContainsText
    End Function

    Private _ContainsFileDropList As Boolean
    Private Sub _thContainsFileDropList(ByVal format As Object)
        Try
            _ContainsFileDropList = Clipboard.ContainsFileDropList
        Catch ex As Exception
            _ContainsFileDropList = False
        End Try
    End Sub
    Public Function ContainsFileDropList() As Boolean
        Dim instance As New ClipboardAsync
        Dim staThread As New Thread(AddressOf instance._thContainsFileDropList)
        staThread.SetApartmentState(ApartmentState.STA)
        staThread.Start()
        staThread.Join()
        Return instance._ContainsFileDropList
    End Function

    Private _GetFileDropList As Specialized.StringCollection
    Private Sub _thGetFileDropList()
        Try
            _GetFileDropList = Clipboard.GetFileDropList
        Catch ex As Exception
            _GetFileDropList = Nothing
        End Try
    End Sub
    Public Function GetFileDropList() As Specialized.StringCollection
        Dim instance As New ClipboardAsync
        Dim staThread As New Thread(AddressOf instance._thGetFileDropList)
        staThread.SetApartmentState(ApartmentState.STA)
        staThread.Start()
        staThread.Join()
        Return instance._GetFileDropList
    End Function
End Class

Here is the CSharp Version:

private class ClipboardAsync
{

private string _GetText;
private void _thGetText(object format)
{
    try {
        if (format == null) {
            _GetText = Clipboard.GetText();
        }
        else {
            _GetText = Clipboard.GetText((TextDataFormat)format);
            
        }
    }
    catch (Exception ex) {
        //Throw ex 
        _GetText = string.Empty;
    }
}
public string GetText()
{
    ClipboardAsync instance = new ClipboardAsync();
    Thread staThread = new Thread(instance._thGetText);
    staThread.SetApartmentState(ApartmentState.STA);
    staThread.Start();
    staThread.Join();
    return instance._GetText;
}
public string GetText(TextDataFormat format)
{
    ClipboardAsync instance = new ClipboardAsync();
    Thread staThread = new Thread(instance._thGetText);
    staThread.SetApartmentState(ApartmentState.STA);
    staThread.Start(format);
    staThread.Join();
    return instance._GetText;
}

private bool _ContainsText;
private void _thContainsText(object format)
{
    try {
        if (format == null) {
            _ContainsText = Clipboard.ContainsText();
        }
        else {
            _ContainsText = Clipboard.ContainsText((TextDataFormat)format);
        }
    }
    catch (Exception ex) {
        //Throw ex 
        _ContainsText = false;
    }
}
public bool ContainsText()
{
    ClipboardAsync instance = new ClipboardAsync();
    Thread staThread = new Thread(instance._thContainsFileDropList);
    staThread.SetApartmentState(ApartmentState.STA);
    staThread.Start();
    staThread.Join();
    return instance._ContainsText;
}
public bool ContainsText(object format)
{
    ClipboardAsync instance = new ClipboardAsync();
    Thread staThread = new Thread(instance._thContainsFileDropList);
    staThread.SetApartmentState(ApartmentState.STA);
    staThread.Start(format);
    staThread.Join();
    return instance._ContainsText;
}

private bool _ContainsFileDropList;
private void _thContainsFileDropList(object format)
{
    try {
        _ContainsFileDropList = Clipboard.ContainsFileDropList();
    }
    catch (Exception ex) {
        //Throw ex 
        _ContainsFileDropList = false;
    }
}
public bool ContainsFileDropList()
{
    ClipboardAsync instance = new ClipboardAsync();
    Thread staThread = new Thread(instance._thContainsFileDropList);
    staThread.SetApartmentState(ApartmentState.STA);
    staThread.Start();
    staThread.Join();
    return instance._ContainsFileDropList;
}

private Specialized.StringCollection _GetFileDropList;
private void _thGetFileDropList()
{
    try {
        _GetFileDropList = Clipboard.GetFileDropList();
    }
    catch (Exception ex) {
        //Throw ex 
        _GetFileDropList = null;
    }
}
public Specialized.StringCollection GetFileDropList()
{
    ClipboardAsync instance = new ClipboardAsync();
    Thread staThread = new Thread(instance._thGetFileDropList);
    staThread.SetApartmentState(ApartmentState.STA);
    staThread.Start();
    staThread.Join();
    return instance._GetFileDropList;
}
}

You can simple use it with: Vb.net:

Dim Clipboard2 As New ClipboardAsync
MessageBox.Show (Clipboard2.ContainsText())

Csharp:

ClipboardAsync Clipboard2 = new ClipboardAsync();
MessageBox.Show (Clipboard2.ContainsText());

score 7 · Answer 4 · answered Dec 18 '15 at 15:35

BoltBait's code did not work for IDataObject because data object loses information outside the thread. Everything works fine, if the IDataObject is used only inside the thread like this:

IDataObject idat = null;
Exception threadEx = null;
String text = "";
Thread staThread = new Thread(
    delegate ()
    {
        try
        {
            idat = Clipboard.GetDataObject();
            text = idat.GetData(DataFormats.Text)
        }

        catch (Exception ex) 
        {
            threadEx = ex;            
        }
    });
staThread.SetApartmentState(ApartmentState.STA);
staThread.Start();
staThread.Join();
// here you can use text, which contains data from clipboard

score 2 · Answer 5 · edited Jan 15 '17 at 15:47

This is a threading problem. We have to get the right thread and execute through delegates.

I am updating my properties through a timer elapsing every 500 ms. Here is the code:

    public delegate void ClipboarDelegate();

    ClipboarDelegate clipboardDelegate = null;

    void clipboardTimer_Elapsed(object sender, ElapsedEventArgs e)
    {
        if (clipboardDelegate == null)
            clipboardDelegate = ClipboarDelegateMethod;

        //Here we get the right thread, most probably the application thread
        Application.Current.Dispatcher.BeginInvoke(clipboardDelegate);
    }

    public void ClipboarDelegateMethod()
    {
        try
        {
            if (Clipboard.ContainsData(DataFormats.Text))
            {
                //It's important to lock this section
                lock (ClipboardString)
                {
                    ClipboardString = Clipboard.GetData(DataFormats.Text) as string;
                }
            }
        }
        catch
        { }
    }

Moreover I've made a proper DependencyProperty with ClipboardString:

    public static readonly DependencyProperty ClipboardStringDP =
        DependencyProperty.Register("ClipboardString",
                                    typeof(string),
                                    typeof(MainWindow),
                                    new UIPropertyMetadata(string.Empty));

    public string ClipboardString
    {
        get { return (string)this.GetValue(ClipboardStringDP); }
        set { this.SetValue(ClipboardStringDP, value); }
    }

This way it can be bound to my TextBox in XAML assuming my control or window x:Name="_this":

<TextBox Name="ClipBoardTextBox"
         DataContext="{Binding ElementName=_this}"
         Text="{Binding Path=ClipboardString, Mode=OneWay}"/>

Is this meant as another answer to the original question? If so, then what does it offer that's new? — ClickRick, Jun 15 '14 at 17:24

score 0 · Answer 6 · answered Feb 06 '09 at 20:11

0

For some reason BoltBait's code didn't quite work (idat was still null even after staThread.Join()). I just did Clipboard.GetText() inside of the staThread delegate instead of Clipboard.GetDataObject() and that worked fine.

Thanks though - your code snippet got me 99% there :)

answered Feb 06 '09 at 20:11

Jonathan Yee

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2
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Hi Jonathan - I saw the exact same thing and did the same thing as well. – Matthew Feb 10 '09 at 00:24

Clipboard.GetText returns null (empty string)

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