当对象的所有属性都已设置时，是否有事件？

Question

想象一个简单的 POCO

public class Test{
    public int ID {get; set;}
    public string Name {get; set;}
    public string SomeProperty {get; set;}
}

有没有办法将这个对象连接起来，以便只有在设置了 所有 属性时才会触发事件？像 InitializeComplete 事件之类的？或者有没有办法轻松创建这样的事件自定义？

谢谢

Answer 1

你可以像这样自己实现：

public delegate void AllPropertiesSetDelegate();
public class Test
{
    public delegate void AllPropertiesSetDelegate(object sender, EventArgs args);

    public int Id
    {
        get => _id;
        set
        {
            _id = value;
            CheckAllProperties();
        }
    }
    private int _id;
    public string Name
    {
        get => _name;
        set
        {
            _name = value;
            CheckAllProperties();
        }
    }
    private string _name;

    private void CheckAllProperties()
    {
        //Comparing Id to null is pointless here because it is not nullable.
        if (Name != null && Id != null)
        {
            AllPropertiesSet?.Invoke(this, new EventArgs());
        }
    }
}

class Program
{
    static void Main(string[] args)
    {
        Test t = new Test();
        t.AllPropertiesSet += delegate { AllPropsSet(); };
        t.Id = 1;
        t.Name = "asd";
        Console.ReadKey();
    }

    static void AllPropsSet()
    {
        Console.WriteLine("All properties have been set.");
    }
}

你自己看看你是否可以让实现更小/更容易处理。

测试代码：

class Program
{
    static void Main(string[] args)
    {
        Test t = new Test();
        t.AllPropertiesSet += delegate { AllPropsSet(); };
        t.Id = 1;
        t.Name = "asd";
        Console.ReadKey();
    }

    static void AllPropsSet()
    {
        Console.WriteLine("All properties have been set.");
    }
}

以下是如何使用反射检查所有非值类型是否为空：

    public static bool AllPropertiesNotNull<T>(this T obj) where T : class
    {
        foreach (var prop in obj.GetType().GetProperties())
        {
            //See if our property is not a value type (value types can't be null)
            if (!prop.PropertyType.IsValueType)
            {
                if (prop.GetValue(obj, null) == null)
                {
                    return false;
                }
            }
        }
        return true;
    }

您可以通过修改 CheckAllProperties 方法在原始代码中使用它：

    private void CheckAllProperties()
    {
        if (this.AllPropertiesNotNull())
        {
            AllPropertiesSet?.Invoke(this, new EventArgs());
        }
    }

Answer 2

如果你想确保一个对象被正确创建，为什么不这样做，所以创建它的唯一方法就是同时设置所有属性。

public class Test{
    public int ID {get; set;}
    public string Name {get; set;}
    public string SomeProperty {get; set;}

    // Constructor
    public Test(int id, string Name, string someProperty)
    {
        this.ID = id;
        this.Name = name;
        this.SomeProperty = someProperty;
    }
}

Answer 3

这是@fstam 答案的一个变体。它在event 上将其更改为完整，并进行调用以更清晰地检查属性。如果你支持我，请支持@fstam。

第一节课：

public class TestPropertyCheck
{
    public event EventHandler AllPropertiesSet;

    public int Id
    {
        get => _id;
        set
        {
            _id = value;
            CheckAllProperties(PropertyNames.Id);
        }
    }
    private int _id;
    public string Name
    {
        get => _name;
        set
        {
            _name = value;
            CheckAllProperties(PropertyNames.Name);
        }
    }
    private string _name;

    public string Address
    {
        get => _address;
        set
        {
            _address = value;
            CheckAllProperties(PropertyNames.Address);
        }
    }
    private string _address;

    private void CheckAllProperties(PropertyNames propName)
    {
        propertiesSet |= propName;
        if (propertiesSet == PropertyNames.AllProps)
        {
            AllPropertiesSet?.Invoke(this, new EventArgs());
        }

    }

    private PropertyNames propertiesSet = PropertyNames.None;

    [Flags]
    private enum PropertyNames
    {
        None = 0,
        Id = 0x01,
        Name = 0x02,
        Address = 0x04,
        AllProps = Id | Name | Address,
    }
}

然后是一个测试程序

public static class PropertyCheckTester
{
    public static void Test()
    {
        var test = new TestPropertyCheck();
        test.AllPropertiesSet += AllPropertiesSet;
        Debug.WriteLine("Setting Name");
        test.Name = "My Name";
        Debug.WriteLine("Setting ID");
        test.Id = 42;
        Debug.WriteLine("Setting Address");
        test.Address = "Your address goes here";

    }

    public static void AllPropertiesSet(object sender, EventArgs args)
    {
        Debug.WriteLine("All Properties Set");
    }
}

还有输出：

Setting Name
Setting ID
Setting Address
All Properties Set

Answer 4

对于具有完整属性的普通类来说，这样的事件相当容易实现（下面的代码来自@fstam 的回答，部分来自头部，告诉我是否有问题，或者以伪代码威胁它）：

public class Test
{
    public EventHandler InitializeCompleted;

    int _id;
    public int Id
    {
        get => _id;
        set
        {
            _id = value;
            CheckAllProperties();
        }
    }

    string _name;
    public string Name
    {
        get => _name;
        set
        {
            _name = value;
            CheckAllProperties();
        }
    }

    HashSet<string> _initialized = new HashSet<string();

    void CheckAllProperties([CallerMemberName] string property = null)
    {
        if(_initialized == null) // ignore calls after initialization is done
            return;
        _initialized.Add(property);
        if(_initialized.Count == 2) // all properties setters were called
        {
            _initialized = null;
            InitializeCompleted?.Invoke(this, EventArgs.Empty);
        }
    }
}

使用反射可以使任务更加简单：您可以获得属性计数器（无需在CheckAllProperties 中维护该数字），标记必须包含/排除的属性。如果您决定这样做，请不要忘记使用惰性模式，只对类型执行一次，而不是对每个实例执行一次。