如何解决这个ComboBox项目设置问题？ [英] How to solve this ComboBox item setting problem?

问题描述

此代码无法为组合框设置正确的值。这是因为，这些是来自不同的上下文。

This code is not setting right value to the combobox. This is because, those are from different contexts.

此外，

In addition, in my actual problem, neither overloading == in nor overriding Equals() in MyClass is working as well.

任何替代方法？

如何解决这个问题？

public class MyClass
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public MyClass(int id, string name)
        {
            ID = id;
            Name = name;
        }

        public static List<MyClass> Get()
        {
            return new List<MyClass>
            {
                new MyClass(2, "AAA"),
                new MyClass(4, "BBB"),
                new MyClass(5, "CCC"),
                new MyClass(7, "DDD"),
                new MyClass(10, "EEE")
            };
        }
    }

ComboBoxForm.cs

ComboBoxForm.cs

public partial class ComboBoxForm : Form
    {
        public ComboBoxForm()
        {
            InitializeComponent();
        }

        private void Form1_Shown(object sender, EventArgs e)
        {
            LoadDataToComboBoxFromDatabase();
        }

        private void LoadDataToComboBoxFromDatabase()
        {
            comboBox1.Items.Clear();

            List<MyClass> list = MyClass.Get();

            foreach(MyClass mc in list)
            {
                comboBox1.Items.Add(mc);
            }

            comboBox1.DisplayMember = "Name";
            comboBox1.ValueMember = "ID";

            comboBox1.SelectedIndex = 0;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            int ID = 5;//This is what I have.
            comboBox1.SelectedItem = .............how?
        }
    }

推荐答案

I相信你的Equals比较可能不正确。对于NHibernate，我使用以下 Equals（）方法：

I believe your Equals comparison may be incorrect. For NHibernate, I use the following Equals() method:

public static class EntityUtil
{
    public static bool Equals(IEntity a, IEntity b)
    {
        // Transient entitys are never equal (unless they are ReferenceEquals)!

        return
            ReferenceEquals(a, b) || (
                !((object)a == null || (object)b == null) &&
                !(IsTransient(a) || IsTransient(b)) &&
                NHibernateProxyHelper.GetClassWithoutInitializingProxy(a) == NHibernateProxyHelper.GetClassWithoutInitializingProxy(b) &&
                a.Id.Equals(b.Id)
            );
    }

    public static bool IsTransient(IEntity entity)
    {
        return entity.Id == 0;
    }
}

我已经在一个单独的帮助类中定义了这个方法，在我的实体中使用：

I have defined this method in a separate helper class and use this in my entity:

public class Entity : IEquatable<Entity>, IEquatable<IEntity>
{
    private int? _hashCode;

    public virtual int Id { get; protected set; }

    public override bool Equals(object obj)
    {
        return EntityUtil.Equals((IEntity)this, obj as IEntity);
    }

    public virtual bool Equals(Entity obj)
    {
        return EntityUtil.Equals((IEntity)this, (IEntity)obj);
    }

    public virtual bool Equals(IEntity obj)
    {
        return EntityUtil.Equals((IEntity)this, obj);
    }

    public static bool operator ==(Entity a, Entity b)
    {
        return EntityUtil.Equals((IEntity)a, (IEntity)b);
    }

    public static bool operator !=(Entity a, Entity b)
    {
        return !(a == b);
    }

    public override int GetHashCode()
    {
        // GetHashCode needs to return a stable value.

        if (!_hashCode.HasValue)
        {
            _hashCode =
                NHibernateProxyHelper.GetClassWithoutInitializingProxy(this).GetHashCode() ^
                ((IEntity)this).Id.GetHashCode();
        }

        return _hashCode.Value;
    }
}

这是与NHibernate 。也许这也有助于你。

This is the suggested implementation for working with equality with NHibernate. Maybe this helps for you too.

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