How do I create a TagHelper whose value is a Property Model (without using @Model)?
Tag Helper is one of the nice features of Asp.Net Core. I have created several tag helpers and they can be very helpful.
Now I would like to try something more advanced. Attributes of tag attributes can be created so that the attribute value is a property of the model.
And an example of this:
//model
public class MyModel{
public int MyField {get;set;} = 10;
}
//in the view
@model MyModel
...
<input asp-for="MyField" />
In the above example, the tag asp-for
for the tag input
refers to a property from the model. The documentation says that
The asp-for attribute value is the model expression and the right side of the lambda expression. Hence, asp-for = "Property1" becomes m => m.Property1 in the generated code, so you don't need to prefix with Model.
So this is pretty cool and this same documentation seems to be called "Expression Name".
How do I create such a property in my own tag helper?
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Just declare the parameter in your TagHelper by type ModelExpression
and then use it to create content.
For example:
public class FooTagHelper : TagHelper
{
public ModelExpression For { get; set; }
public override void Process(TagHelperContext context, TagHelperOutput output)
{
output.TagName = "div";
output.Content.SetHtmlContent(
$@"You want the value of property <strong>{For.Name}</strong>
which is <strong>{For.Model}</strong>");
}
}
If you use it like this:
@model TestModel
<foo for="Id"></foo>
<foo for="Val"></foo>
And pass the model of the type new TestModel { Id = "123", Val = "some value" }
, then you will get the following result in your view (formatted for clarity):
<div>
You want the value of property <strong>Id</strong>
which is <strong>123</strong>
</div>
<div>
You want the value of property <strong>Val</strong>
which is <strong>some value</strong>
</div>
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