利用反射代替switch

weixin_34198881發表於2019-01-08
反射

根據傳進來不同的值，呼叫不同的方法

View Code 
protected void btn_SwitchClick(object sender, EventArgs e)
{
    string result = "";
    switch (ddlMethod.SelectedValue)
    {
        case "A":
            result = SwitchTest.GetA();
            break;
        case "B":
            result = SwitchTest.GetB();
            break;
        case "C":
            result = SwitchTest.GetC();
            break;
        default:
            result = ddlMethod.SelectedValue + "方法找不到";
            break;

    }
    ltrResult.Text = result;
}

下面利用反射機制實現，首選需要一個自定義屬性類

View Code 
public class ActionMethodAttribute:Attribute
{
    public string ActionTypeName;

    public ActionMethodAttribute(string typeName)
    {
        this.ActionTypeName = typeName;
    }
}

然後定義一個基類

View Code 
public abstract class GenericBLL
{
    public Hashtable GetMethodAttribute<T>(T t)
    {
        Hashtable ht = new Hashtable();
        Hashtable obj = CacheHandler<Hashtable>.GetCache(t.ToString());
        if (obj == null)
        {
            Type type = t.GetType();
            foreach (MethodInfo mi in type.GetMethods())
            {
                ActionMethodAttribute[] mis = (ActionMethodAttribute[])mi.GetCustomAttributes(typeof(ActionMethodAttribute), false);
                foreach (ActionMethodAttribute actionMethodAttribute in mis)
                {
                    string actionName = actionMethodAttribute.ActionTypeName;
                    ht.Add(actionName, mi);
                }
            }
            CacheHandler<Hashtable>.SetCache(t.ToString(), ht);
        }
        else
        {
            ht = (Hashtable)obj;
        }
        return ht;
    }

    /// <summary>
    /// return message;
    /// </summary>
    /// <param name="actionName"></param>
    /// <returns></returns>
    public string DoAction(string actionName)
    {
        string message;
        Hashtable ht = GetMethodAttribute(this);
        if (ht.Contains(actionName))
        {
            message = ((MethodInfo)ht[actionName]).Invoke(this, new object[] { }).ToString();
        }
        else
        {
            message = string.Format("{0} Not Defined.!", actionName);
            //throw new Exception(errmsg);
        }
        return message;
    }
}

實現類繼承，

View Code 
public class ReflectTest:GenericBLL
{                   
    [ActionMethod("A")]
    public string GetA()
    {
        return "呼叫的A";
    }

    [ActionMethod("B")]
    public string GetB()
    {
        return "呼叫的B";
    }


    [ActionMethod("C")]
    public string GetC()
    {
        return "呼叫的C";
    }
}

具體的呼叫

View Code 
protected void btn_ReflectClick(object sender, EventArgs e)
{
    string result = ReflectTest.DoAction(ddlMethod.SelectedValue);
    ltrResult.Text = result;
}

ASPX中的程式碼如下

View Code 
選D會提示沒有D方法
<asp:DropDownList ID="ddlMethod" runat="server">
    <asp:ListItem Text="A" Value="A">
    </asp:ListItem>
    <asp:ListItem Text="B" Value="B">
    </asp:ListItem>
    <asp:ListItem Text="C" Value="C">
    </asp:ListItem>
    <asp:ListItem Text="D" Value="D">
    </asp:ListItem>
</asp:DropDownList>
<br />
<asp:Button ID="btnInvoke" Text="Switch" OnClick="btn_SwitchClick" runat="server" />
<asp:Button ID="btnInvokeR" Text="Reflect" OnClick="btn_ReflectClick" runat="server" />
<br>
<asp:Literal ID="ltrResult" runat="server" />

原始碼下載： ActionMethod.rar

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