Accessing attributes of a WPF application from another thread in main application

Question

I started a WPF application on a thread of my main application.

Now I want to access a text box in this WPF application from the main thread.

I was trying to use dispatchers but I could not figure out a way.

Here is my code

  class program
{
    public static event MyEventHandler event1;
    static Application a;
    static void fun()
    {
        a = new Application();
        a.StartupUri = new Uri("MainWindow.xaml", System.UriKind.Relative);
        //a.initializeComponent();
        a.Run();

    }

     //[STAThread]
    static void Main(string[] args)
    {
        Thread newThread = new Thread(new ThreadStart(fun));
        newThread.SetApartmentState(ApartmentState.STA);
        newThread.Start();
        Trace.WriteLine("rest");
        //I WANT TO ACCESS THE TEXT BOX FROM HERE 


    }
}

Where are you trying to access an attribute? What attribute are you trying to access? There isn't enough information to see what you have tried to make this work. — Martin Noreke, May 25 '15 at 17:47
@MartinNoreke I tried to elaborate. Suggestions appreciated. — vasu, May 25 '15 at 17:58

score 3 · Answer 1 · edited May 23 '17 at 12:05

3

the main thread needs a reference to the window and/or textbox
- Have the thread that creates the window/textbox put a reference to the window/textbox in a static variable
When the main thread wants to access the textbox it has to switch to the thread that created the textbox and get the result from that thread.
- Only the thread that created a control can safely access that control. See this question How to update the GUI from another thread in C#?

From an answer on that question:

string x;
TheTextBox.Dispatcher.BeginInvoke((Action)(() => x = TheTextBox.Text));

edited May 23 '17 at 12:05

Community

1
1

answered May 25 '15 at 18:07

Emond

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would be thankful if you could elaborate on point one. I already have a reference to Application i.e. a . But I cannot get a reference to my current WPF application (how do I get that?). Without it, I cannot reference "TheTextBox" here. – vasu May 26 '15 at 07:20
What do you mean by the current application? The code only contains a single application and you can get it by using App.Current – Emond May 26 '15 at 08:55

score 0 · Answer 2 · answered May 25 '15 at 18:08

You will probably need to do something like this to loop the active windows of the application to find the window you need, then call a method on that window to get the actual text box element you need.

    public void AccessTextBox(string windowName, string textBoxName)
    {
        foreach (Window windowToCheck in a.Windows)
        {
            if (!windowToCheck.Name.Equals(windowName, textBoxName))
                continue;
            windowToCheck.Dispatcher.Invoke(((WindowTypeName)windowToCheck).AccessTextBox(textBoxName));
        }
    }

The Dispatcher.Invoke call is a call that puts you on the UI thread, executes a call the the specified method, and returns to your current thread.

This is psuedo-code (quite ugly too :) ), but should put you on the right path.

Accessing attributes of a WPF application from another thread in main application

2 Answers2