[英]Generic Method with optional generic parameter
How do I create a generic method with an optional generic type? 如何创建具有可选泛型类型的泛型方法? This is what I have right now, which works
这就是我现在所拥有的,这是有效的
public GridViewColumn<T> Column<D>(String HeaderText, D decorator) where D: IColumnDecorator, new()
{
GridViewColumn<T> column = new GridViewColumn<T>();
column.HeaderText = HeaderText;
column.Decorator = new D();
return column;
}
As you can see, I need to instantiate the type D (implements IColumnDecorator) inside the Column() method. 如您所见,我需要实例化Column()方法中的类型D(实现IColumnDecorator)。
The issue is, the type "D" is optional. 问题是类型“ D”是可选的。 If Null, I want to explicitly use a default ColumnDecorator that I have.
如果是Null,我想明确使用我拥有的默认ColumnDecorator。 something like
就像是
public GridViewColumn<T> Column<D>(String HeaderText, D decorator) where D: IColumnDecorator, new()
{
GridViewColumn<T> column = new GridViewColumn<T>();
column.HeaderText = HeaderText;
if(decorator ==null)
{
column.Decorator = new DefaultColumnDecorator();
}
else{
column.Decorator = new D();
}
return column;
}
Please help. 请帮忙。 Thanks!
谢谢!
[Edit]. [编辑]。
Here is how I want to use it in razor MVC if I have a custom IColumnDecorator implementation 如果我有一个自定义IColumnDecorator实现,这就是我想在razor MVC中使用它的方式
@Model.[IEnumerable].Grid(grid=>{
..
...
grid.columns(
grid.Column<MyOwnColumnDecorator>("FirstColumn")
)
});
If I don't have any and want to use default, then I want to be able to do something like 如果我没有任何内容并想要使用默认值,那么我希望能够执行类似的操作
@Model.[IEnumerable].Grid(grid=>{
..
...
grid.columns(
grid.Column("FirstColumn",null) or simply grid.Column("FirstColumn");
)
});
In your current code, you don't need the decorator
parameter since you create a new instance of D
and use that instead. 在当前代码中,由于创建了
D
的新实例并使用了它,因此不需要decorator
参数。
public GridViewColumn<T> Column<D>(String HeaderText) where D: IColumnDecorator, new()
{
GridViewColumn<T> column = new GridViewColumn<T>();
column.HeaderText = HeaderText;
column.Decorator = new D();
return column;
}
If you have a default parameter type to use, you don't need to use generics: 如果要使用默认参数类型,则无需使用泛型:
public GridViewColumn<DefaultColumnDecorator> Column(String headerText)
{
return Column<DefaultColumnDecorator>(headerText);
}
Alternatively you could keep the parameter and remove the new()
constraint: 或者,您可以保留参数并删除
new()
约束:
public GridViewColumn<T> Column<D>(String HeaderText, D decorator) where D : IColumnDecorator
{
GridViewColumn<T> column = new GridViewColumn<T>();
column.HeaderText = HeaderText;
column.Decorator = decorator;
return column;
}
public GridViewColumn<DefaultColumnDecorator> Column(String headerText)
{
return Column(headerText, new DefaultColumnDecorator());
}
Use a default parameter: 使用默认参数:
public GridViewColumn<T> Column<D,T>(string HeaderText, D decorator = null)
where D : IColumnDecorator, class, new()
You shouldn't be instantiating type D
from the Column
method. 您不应该从
Column
方法实例化类型D
Instead, you should let the caller pass it in. 相反,你应该让调用者传入它。
public GridViewColumn<T> Column(String HeaderText, IColumnDecorator decorator)
{
GridViewColumn<T> column = new GridViewColumn<T>();
column.HeaderText = HeaderText;
if(decorator ==null)
{
column.Decorator = new DefaultColumnDecorator();
}
else{
column.Decorator = decorator;
}
return column;
}
The rationale is here: http://en.wikipedia.org/wiki/Dependency_injection 理由如下: http : //en.wikipedia.org/wiki/Dependency_injection
After playing with some options I made a sample that works with the following code: 在玩了一些选项后,我制作了一个使用以下代码的示例:
public GridViewColumn<TResult> Column<TColumn>(string HeaderText, TColumn decorator = null) where TColumn : class, IColumnDecorator
{
GridViewColumn<TResult> column = new GridViewColumn<TResult>();
column.HeaderText = HeaderText;
if(decorator == null)
{
column.Decorator = new DefaultColumnDecorator();
}
else
{
column.Decorator = decorator;
}
return column;
}
In order to make this work you need to consider the following: 为了使这项工作,您需要考虑以下几点:
In my sample I was able to call this method in the following two ways with the same result: 在我的示例中,我能够通过以下两种方式调用此方法,结果相同:
@Model.[IEnumerable].Grid(grid=>{
..
...
grid.columns(
grid.Column<MyOwnColumnDecorator>("FirstColumn",null);
)
});
@Model.[IEnumerable].Grid(grid=>{
..
...
grid.columns(
grid.Column<MyOwnColumnDecorator>("FirstColumn");
)
});
Good luck! 祝好运!
There's a lot of ways to do what you're trying to do, how about asking the caller to pass a way to make a decorator? 有很多方法可以做你正在尝试做的事情,如何要求调用者通过一种方式来制作装饰器?
public GridViewColumn<T> Column(string HeaderText, Func<IColumnDecorator> decoratorGenerator)
{
GridViewColumn<T> column = new GridViewColumn<T>();
column.HeaderText = HeaderText;
column.Decorator = decoratorGenerator != null ? decoratorGenerator()
: new DefaultColumnDecorator() ;
return column;
}
I see two things you are missing. 我看到你遗失的两件事。 One is a default parameter setting
decorator = null
and the other is the use of default(T)
. 一个是默认参数设置
decorator = null
,另一个是default(T)
。 I have rewrote yours as follows but I can't test it obviously - should be close though. 我把你的重写如下,但我显然无法测试它 - 应该尽可能接近。
public GridViewColumn<TResult> Column<TColumn>(string HeaderText, TColumn decorator = null) where TColumn : IColumnDecorator, new()
{
GridViewColumn<TResult> column = new GridViewColumn<TResult>();
column.HeaderText = HeaderText;
column.Decorator = decorator == null ? new DefaultColumnDecorator() : default(TColumn);
return column;
}
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