How to Safely Access Windows Forms Controls from Background Threads?

Cross -threaded access in the Windows window: understand and solve the "invalid control access" error

When using Windows windows in C#, in some cases, "invalid cross -threading operation" may be encountered. This error occurs when you tried to access the control from a thread outside the creation of the control. When trying to perform data operations that may block UI threads, this problem usually occurs, so as to indicate that developers use background threads for data loading.

Understand the problem

In the scenario provided, you try to load data on a separate thread, and UI (including user control) is created on the main thread. When the user -controlled LOAD event access control control (e.g., check the value of the text box), the "invalid cross -threading operation" error will be triggered. This is because the control was created on the main thread, and it visited it from another thread to violate the thread association rules.

Use InvokeRequired Security Access Control

A possible solution is to use the controlling attribute of the control. This attribute indicates whether the current thread is the same as the thread created by the control. If it returns true, it means you need to call the code on the right thread. code example 1

In this example, the first line check whether the InvokeRequired is true. If so, call the code block on the correct thread to ensure the correct access to the UI. alternative: indirect access control value

UserContrl1_LoadDataMethod()
{
    if (textbox1.InvokeRequired) // 第 1 行
    {
        this.Invoke(new MethodInvoker(UserContrl1_LoadDataMethod));
        return;
    }

    if (textbox1.Text == "MyName") // 现在不会引发异常
    {
        // 加载与“MyName”对应的数据
        // 填充稍后将绑定到网格的全局变量 List<string>
    }
}

Another method is to indirectly obtain control value. Do not access the control directly from the background thread, but retrieve their values ​​on the main thread and pass it to the background working device.

In this case, the text box value is retrieved on the main thread and stored in a local variable. Then, the data loading operation on the background thread can use this variable safely.

Conclusion

UserContrl1_LOadDataMethod()
{
    string name = "";
    if (textbox1.InvokeRequired)
    {
        textbox1.Invoke(new MethodInvoker(delegate { name = textbox1.Text; }));
    }
    if (name == "MyName")
    {
        // 执行任何操作
    }
}

In order to avoid "invalid cross -threading operation" abnormalities, please keep in mind that comply with thread association rules and create their thread access control. Use InvokeRequired to update the control safely from other threads, or consider using indirect access methods to retrieve the control value on the correct thread.

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