C＃如果在foreach中使用

Question

The Code below resets form labels to "0". Out of curiosity, I am trying to figure out how to access only certain items rather than every item in the List. The foreach function works great here but in other parts of the code I would like to access and modify these objects diferently

For example how could I set every other field to "0" or set only the last or first three to some value, etc.

// Set the form Labels to "0"
private void btnClear_Click(object sender, EventArgs e)
{
    // Create List of Labels for modifying form
    new List<Label>() { lbl1, lbl2, lbl3, lbl4, lbl5, lbl6 }.ForEach(p => p.Text = "0");
}

Thank You

Update:

Well after lots of reading and testing I came back to the most basic method for selecting every other item in the list.

        // Set the form Labels to "0"
    private void btnClear_Click(object sender, EventArgs e)
    {
        // Create List of Labels for modifying form
        List<Label> lbl = new List<Label>() { lbl1, lbl2, lbl3, lbl4, lbl5, lbl6 };
        int x =1; //  Set to get every other label. 0 = even, 1 = odd
        while (x < lbl.Count)
        {
            lbl[x].Text = "0";
            x = x + 2;
        }

@Jonathan Wood is there a method to this with the items.ForEach(p => { some code(), p.Text = "0"; });

Answer 1

The delegate that you pass to ForEach() can be enclosed in curly braces, which allows you to define more complex logic such as if statements.

items.ForEach(p => { if (p != null) p.Text = "0"; });

You can even define your delegate as a separate method and just pass that.

However, I wonder about your approach. Is this a winforms app? Why not just do a regular loop that loops through controls on the form? Then the additional table won't be necessary.

Answer 2

To set every other field to "0" you could try the IEnumerable.Where overload that passes the index of current element to the predicate.

Let's say you want to work on the elements with odd index:

new List<Label>() { lbl1, lbl2, lbl3, lbl4, lbl5, lbl6 }.Where((p, i) => (i & 1) == 1).ToList().ForEach(p => p.Text = "0");

Answer 3

You can use Linq:

first three:

var labels = new List<Label>() { lbl1, lbl2, lbl3, lbl4, lbl5, lbl6 };
foreach(Label lbl in labels.Take(3))
    lbl.Text = someValue;

last three:

foreach(Label lbl in labels.Reverse().Take(3))
    lbl.Text = someValue;

other labels:

var allLabels = this.Controls.OfType<Label>();
var otherLabels = allLabels.Except(labels);
foreach(Label lbl in otherLabels)
    lbl.Text = "0";

Answer 4

Set first 3 to 0

new List<Label>() { lbl1, lbl2, lbl3, lbl4, lbl5, lbl6 }.Take(3).ForEach(p => p.Text = "0");

Set last 3 to 0

new List<Label>() { lbl1, lbl2, lbl3, lbl4, lbl5, lbl6 }.Skip(3).Take(3).ForEach(p => p.Text = "0");