如何为多个类似控件编写事件处理程序？

Question

Basically I have certain controls where they do similar things but for different controls using different values. For instance:

public static void DeleteItemsFromList ( object sender, EventArgs e )
{
    ListBox control = null;
    switch ( ( ( Button ) sender ).Name )
    {
        case "EffectsRemove": control = ( ListBox ) ActiveForm [ "EffectsList" ]; break;
        case "LayersRemove": control = ( ListBox ) ActiveForm [ "LayersList" ]; break;
        case "ObjectsRemove": control = ( ListBox ) ActiveForm [ "ObjectsList" ]; break;
    }

    control.Items.Add ( ( ( Button ) sender ).Name )

    string action = null;
    switch ( ( ( CheckButton ) sender ).Name )
    {
        case "EffectsRemove": action = "Effects"; break;
        case "LayersRemove": action = "Layers"; break;
        case "ObjectsRemove": action = "Objects"; break;
    }

    var selectedItem = control.SelectedItem;
    if ( selectedItem == null )
        return;

    Refresh = false;
    UpdateUI ( action );
    Refresh = true;
}

Is this bad practice? Is there a better way to do these kinds of variable event handlers based on similarly behaving controls?

Answer 1

Personally I find your example leaves too many opportunities for error. Your best bet would be to extract the common functionality to a separate method.

public static void EffectsRemove_Click(object sender, EventArgs e)
{
    DeleteItemsFromList(
        (Button)sender, 
        (ListBox)ActiveForm["EffectsList"], 
        "Effects");
}

public static void LayersRemove_Click(object sender, EventArgs e)
{
    DeleteItemsFromList(
        (Button)sender, 
        (ListBox)ActiveForm["LayersList"], 
        "Layers");
}

public static void ObjectsRemove_Click(object sender, EventArgs e)
{
    DeleteItemsFromList(
        (Button)sender, 
        (ListBox)ActiveForm["ObjectsList"], 
        "Objects");
}

public static void DeleteItemsFromList(
    Button sender, 
    ListBox control, 
    string action)
{
    control.Items.Add(sender.Name);

    var selectedItem = control.SelectedItem;
    if ( selectedItem == null )
        return;

    Refresh = false;
    UpdateUI action;
    Refresh = true;
}

Answer 2

我可以看到您想要重用逻辑的愿望，但是在我看来，这种使代码更脆弱且更难以维护的方法，在这种情况下，即使代码是伪相似的，我可能也希望使用单独的偶数处理程序。

Answer 3

Here's another approach you could use via some delegates defined while subscribing to the EventHandler. I think it's a bit easier to read this way, but could get out of hand if you added several other conditions (like if RichTextBox, if Combobox, etc.)

    private void Form1_Load(object sender, EventArgs e)
    {
        button1.Click += new EventHandler(delegate { DoButtonProcessing(this, "EffectsList", null); });
        button2.Click += new EventHandler(delegate { DoButtonProcessing(this, "LayersList", null); });

        button3.Click += new EventHandler(delegate { DoButtonProcessing(this, null, "Effects"); });
        button4.Click += new EventHandler(delegate { DoButtonProcessing(this, null, "Layers"); });
    }

    void DoButtonProcessing(object sender, string list, string action)
    {
        ListBox control = (ListBox)ActiveForm[list]; //can be null here, but your source also allowed that so I assume it's just a snippit.
        control.Items.Add(((Button)sender).Name);
        var selectedItem = control.SelectedItem;
        if (selectedItem == null) return;
        Refresh = false;
        UpdateUI null;
        Refresh = true;

    }

Answer 4

You may want to consider using a custom control, where you can derive from Button, and add a few properties to each instance of your CustomButton, representing the string and ListBox that you care about. Then you can tie each button to the same event handler, and act on the properties of the CustomButton, without caring about which one it is.