C# - 如何检查字符串值是否在不同的类中发生了变化？

Question

I have a class as follows:

class TestSomeData
{
    public string someString;
    public void CheckSomeStuff()
    {
         foreach(string x in someList)
         {
              someString = x;
          }
     }
 }

What i want to do is this:

TestSomeData test = new TestSomeData;
test.CheckSomeStuff();
label1.Content = test.someString;

So if x is 1,2,3,4,5 out of someList in CheckSomeStuff, i need the label1.Content to reflect that, but from a different class. how do i do that?

Answer 1

A class can inform other classes of changes made to it by declaring events

public class SomeDataClass
{
    public event EventHandler SomeDataChanged;

    private string _someData;
    public string SomeData
    {
        get { return _someData; }
        set
        {
            if (value != _someData) {
                _someData = value;
                OnSomeDataChanged();
            }
        }
    }

    private void OnSomeDataChanged()
    {
        SomeDataChanged?.Invoke(this, EventArgs.Empty);
    }
}

class InterestedClass
{
    public void Work()
    {
        var someData = new SomeDataClass();
        someData.SomeDataChanged += someData_SomeDataChanged;
        someData.SomeData = "New Value";
    }

    void someData_SomeDataChanged(object sender, EventArgs e)
    {
        Console.WriteLine("Some data changed: {0}", ((SomeDataClass)sender).SomeData);
    }
}

You could also make the event static. This would allow a listener to listen to changes of any instance of this class.

SomeDataClass.SomeDataChanged += SomeDataClass_SomeDataChanged;

var someData = new SomeDataClass();
someData.SomeData = "New Value";
var someOtherData = new SomeDataClass();
someData.SomeData = "Other Value";

Answer 2

You could pass a reference to the control so that you can change its text directly. Not saying this design is particularly pretty but it would get the job done.

class TestSomeData
{
    public TestSomeData(Label myControl) {
        this.MyControl = myControl;
    }

    private Label MyControl { get; set; }

    public void CheckSomeStuff()
    {
         if (this.MyControl == null) {
             // throw ArgumentNullException or InvalidOperationException
         }

         foreach(string x in someList)
         {
              this.MyControl.Content = x;
         }
     }
 }

Also as others have noted, the control will always have the last value found in the list. If you're trying to have the label display each value as the list enumerates you're going to have to add some UI logic to force the control to refresh or repaint.

Answer 3

You should make that field static . All instances of that class will have that something in common. Any change will be globally.