Introduction

In WinForms, Control.BeginInvoke marshals work back onto the UI thread. Both MethodInvoker and Action can be used for parameterless callbacks, so the real question is not correctness but readability, compatibility, and how much flexibility you need.

What BeginInvoke Wants

Control.BeginInvoke accepts a Delegate. That means any compatible delegate type can be passed in, including:

• 'MethodInvoker'
• 'Action'
• a custom delegate type

For a simple UI update, both of these are valid:

1textBox1.BeginInvoke((MethodInvoker)(() =>
2{
3    textBox1.Text = "Updated";
4}));
5
6textBox1.BeginInvoke((Action)(() =>
7{
8    textBox1.Text = "Updated";
9}));

In modern code, both produce the same practical outcome: the lambda is queued to the UI thread.

What MethodInvoker Represents

MethodInvoker is a WinForms-oriented delegate type with signature void Method(). It communicates intent clearly: this is a simple UI callback with no parameters and no return value.

That can make old WinForms code easier to scan:

1private void UpdateStatus(string message)
2{
3    if (InvokeRequired)
4    {
5        BeginInvoke((MethodInvoker)(() => statusLabel.Text = message));
6        return;
7    }
8
9    statusLabel.Text = message;
10}

The benefit here is mostly semantic. A reader familiar with WinForms immediately recognizes it as a UI-marshaling pattern.

What Action Adds

Action is the general-purpose delegate family in .NET. For BeginInvoke, the non-generic Action works for parameterless callbacks, and Action<T> variants are useful elsewhere in the codebase for delegates with arguments.

That means Action is often preferable if you want consistency across modern .NET code:

1private void AppendLineSafe(string line)
2{
3    if (InvokeRequired)
4    {
5        BeginInvoke((Action)(() => listBox1.Items.Add(line)));
6        return;
7    }
8
9    listBox1.Items.Add(line);
10}

If the rest of the application already uses Action heavily, this is often the cleaner choice.

Is There a Performance Difference

In real WinForms code, the difference is negligible. UI marshaling, message pumping, and actual UI work dominate. Choosing between MethodInvoker and Action is not a meaningful performance optimization.

So the better decision criteria are:

• codebase consistency
• clarity for the team
• target framework compatibility

On very old framework targets, MethodInvoker may appear more often simply because it was part of the classic WinForms style long before lambdas and pervasive Action usage became common.

What About Parameters

If you need parameters, the simplest approach is still to capture them in a lambda:

string message = "Saved";
BeginInvoke((Action)(() => statusLabel.Text = message));

That means you rarely need a custom delegate just to pass one value into a UI-thread callback.

Recommended Rule of Thumb

Use MethodInvoker when you want to emphasize "this is a classic WinForms UI callback." Use Action when you want consistency with the rest of modern .NET delegate usage.

Neither is wrong. The important part is that UI code stays clearly marshaled and does not touch controls from worker threads directly.

Common Pitfalls

The biggest mistake is focusing on delegate type while ignoring thread affinity. The real bug is updating controls from a background thread without Invoke or BeginInvoke.

Another mistake is assuming BeginInvoke waits for completion. It does not. It posts work asynchronously to the UI thread and returns immediately.

A third issue is overcomplicating the code with custom delegates when a lambda plus Action or MethodInvoker is enough.

Summary

• 'Control.BeginInvoke accepts either MethodInvoker or Action for parameterless callbacks.'
• 'MethodInvoker is WinForms-specific and can make UI intent explicit.'
• 'Action is more general and often fits modern .NET style better.'
• The performance difference is negligible for normal UI work.
• The important rule is to marshal UI updates correctly, not to obsess over delegate flavor.