How Can I Pass Extra Parameters to Event Handlers in C#?

Access extra parameters in event handler

Suppose you need to pass additional data to the event handler. For example, we have a setup method that assigns event handlers:

<code class="language-csharp">private void setup(string someData)
{
     Object.assignHandler(evHandler);
}</code>

And the event handler evHandler needs to access the someData parameter:

<code class="language-csharp">public void evHandler(Object sender)
{
    // 需要在此处使用 someData!!!
}</code>

Solution

To pass additional parameters to an event handler, you can use a lambda expression as a delegate. Instead of assigning the evHandler method directly, we assign a lambda expression that takes the sender object as the first argument and someData as the second argument:

<code class="language-csharp">private void setup(string someData)
{
     Object.assignHandler((sender) => evHandler(sender, someData));
}</code>

Now, the evHandler method can accept both the sender and the someData parameters:

<code class="language-csharp">public void evHandler(Object sender, string someData)
{
    // 访问发送者和 someData
}</code>

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