[英]Optional Parameters in Abstract method? Is it possible?
I have a abstract base class. 我有一个抽象基类。
I have 2 derived classes from this base class. 我有2个从该基类派生的类。
Is there anyway that one of my classes can ignore the string parameter in the abstract overide usage? 无论如何,我的一个类可以忽略抽象覆盖用法中的string参数吗? Or do I have to just send in a blank one and ignore it?
还是我只需要发送一个空白的邮件而忽略它? (making readability drop slightly)
(使可读性略有下降)
Can I have one function that has some sort of optional parameter so that both of the following derived classes would compile? 我是否可以使用一个具有某种可选参数的函数,以便以下两个派生类都可以编译?
PS - The following code is riddled with in-compilable code for the example of what I would like to do PS-下面的代码充满了不可编译的代码,作为我想做的示例
PS PS - Yes i have compiled the following code already - see above comment for outcome PS PS-是的,我已经编译了以下代码-有关结果,请参见上面的注释
public abstract class MyBaseClass
{ //optional string?
public abstract void FunctionCall(int i, string s = "");
}
public class MyDerivedClass : MyBaseClass
{
public override void FunctionCall(int i)
{
MessageBox.Show(i.ToString());
}
}
public class YourDerivedClass : MyBaseClass
{
public override void FunctionCall(int i, string s)
{
MessageBox.Show(s + " " + i.ToString());
}
}
If you don't absolutely need FunctionCall to be abstract, you can declare two versions of it: 如果您绝对不需要FunctionCall是抽象的,则可以声明它的两个版本:
public abstract class MyBaseClass
{
public virtual void FunctionCall(int i)
{
this.FunctionCall(i, "");
}
public virtual void FunctionCall(int i, string s)
{
}
}
public class MyDerivedClass : MyBaseClass
{
public override void FunctionCall(int i)
{
MessageBox.Show(i.ToString());
}
}
public class YourDerivedClass : MyBaseClass
{
public override void FunctionCall(int i, string s)
{
MessageBox.Show(s + " " + i.ToString());
}
}
Otherwise, if it must be abstract to ensure it is implemented, you could still add two versions, it just makes the inheritors more verbose: 否则,如果必须抽象它以确保实现,则仍可以添加两个版本,这只会使继承者更加冗长:
public abstract class MyBaseClass
{
public abstract void FunctionCall(int i);
public abstract void FunctionCall(int i, string s);
}
public class MyDerivedClass : MyBaseClass
{
public override void FunctionCall(int i, string s)
{
throw new NotImplementedException();
}
public override void FunctionCall(int i)
{
MessageBox.Show(i.ToString());
}
}
public class YourDerivedClass : MyBaseClass
{
public override void FunctionCall(int i)
{
throw new NotImplementedException();
}
public override void FunctionCall(int i, string s)
{
MessageBox.Show(s + " " + i.ToString());
}
}
It will throw a compile error: "Abstract Inherited member 'MyBaseClass.FunctionCall(int, string)' is not implemented". 它将引发编译错误:“未实现Abstract继承的成员'MyBaseClass.FunctionCall(int,string)'”。
So no, the short answer is you can't do this. 所以不,简短的答案是您不能这样做。
Instead, you would have to do method overloading and implement BOTH abstract methods. 相反,您将必须进行方法重载并实现两个抽象方法。
public abstract class MyBaseClass
{
public abstract void FunctionCall(int i);
public abstract void FunctionCall(int i, string s = "");
}
public class MyDerivedClass : MyBaseClass
{
public override void FunctionCall(int i, string s = "") { }
public override void FunctionCall(int i)
{
MessageBox.Show(i.ToString());
}
}
public class YourDerivedClass : MyBaseClass
{
public override void FunctionCall(int i, string s)
{
MessageBox.Show(s + " " + i.ToString());
}
public override void FunctionCall(int i) {}
}
However this seems quite messy. 但是,这似乎很混乱。 Perhaps the best option is to always use the optional parameter and simply not pass in a value if it is not needed or handle it as you already seem to be doing.
也许最好的选择是始终使用可选参数,并且在不需要时根本不传递值,或者像您已经在做的那样处理它。
public class MyDerivedClass : MyBaseClass
{
public override void FunctionCall(int i, string s = "")
{
if (!string.IsNullOrEmpty(s))
MessageBox.Show(i.ToString());
else
// handle other path here
}
}
One possible way is to use extension methods to add missing overrides (which also works with interfaces) 一种可能的方法是使用扩展方法添加缺少的替代(也适用于接口)
static class MyBaseClassExtensions
{
public void FunctionCall(MyBaseClass this item, int i)
{
item.FunctionCall(i, null);
}
}
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