为要传递给Partial View的模型设置默认值

Question

I have a partial view that is called from another partial view (kind of nested partial views).

The outer partial view is called Company and the inner partial view is a custom control called searchHelp. Both accept a parameter.

Now the Company view gets a parameter of type company and searchHelper accepts an optional string. This part works fine as I am testing the model value for null and assigning is default text as @((Model==null)?"Enter Text":Model) when used in other views even without passing a parameter.

In my case of nested views, if I dont provide a string as model for searchHelper then it takes company as model from the outer view ie company and gives an error.

Answer 1

The @model definition is not a value setter, it's merely telling Razor what type of view to instantiate. You can't define a default value here. If you don't pass a model to your partial, then it will use the model of the parent view, which is Company in this case. Company is not a string, obviously, so you get that error. If you want to pass a default value for the partial, do that in the second parameter to Html.Partial :

@Html.Partial("searchHelp", Model.SomeStringProperty ?? "Enter Text")

Answer 2

You can assign a default value to the string-as-model from where it's called in the view:

//null coalesce to default string value:
@Html.Partial("searchHelp", Model.searchHelp ?? "default value")  

...though you might do better using an htmlhelper, where you can define the default value just one time:

public IHtmlString SearchHelp(this HtmlHelper html, string searchHelp = "default value")
{
    // make html here
}

Then

@Html.SearchHelp(Model.searchHelp);