Code-Behind
Introduction
To create interactivity for the Typed JSON classes, code-behind classes can be added to extend existing Typed JSON. This is done using .json.cs
files, which are partial definitions for Typed JSON classes.
Create Code-Behind Files
To create a Typed JSON class with code-behind, choose New item
in Visual Studio and then select Starcounter Typed JSON with Code-behind
. By creating one of these with the filename "Person", two files will be created:
{
}
using Starcounter;
namespace MyApp
{
partial class PersonPage : Json
{
}
}
Handling Input Events
Consider this JSON object with a property that is writable from the client:
{
"FirstName$": ""
}
To observe changes to this property, the code-behind method Handle
can be used:
partial class PersonPage : Json
{
void Handle(Input.FirstName action)
{
if (action.Value == "Albert")
{
Message = "You are not allowed to enter Albert. There can be only one.";
action.Cancel();
}
}
}
The Handle
method gets called with a parameter of type Input
. Input
is the base class for events triggered by the client.
The Input
class is auto generated per each JSON view-model. It provides the following properties and methods:
property
Value
- contains the new value of the user inputproperty
OldValue
- contains the current value of the user inputproperty
ValueChanged
- boolean, true if the new value is different than the old valuemethod
Cancel()
- reject the new value. It prevents the propagation of the new value to JSON as well as to the bound data objectproperty
Cancelled
- boolean, true if theCancel()
method was called
To get many more examples of how interactivity is handled, take a look at the KitchenSink repo where the most common UI patterns are demonstrated.
Referring to Nested Objects
JSON-by-example might contain nested objects. For example:
{
"Name": {
"FirstName$": "",
"LastName$": ""
},
"FullName$": ""
}
Code-behind for the root level and Name
-level can be provided as two separate partial classes. For example:
partial class PersonPage : Json
{
void Handle(Input.FullName action)
{
var words = action.Value.Split(' ');
this.Name.FirstName = words[0];
this.Name.LastName = words[1];
}
[PersonPage_json.Name]
partial class PersonPageName : Json
{
void Handle(Input.FirstName action)
{
var person = this.Parent as PersonPage;
person.FullName = action.Value + " " + this.LastName;
}
void Handle(Input.LastName action)
{
var person = this.Parent as PersonPage;
person.FullName = this.FirstName + " " + action.Value;
}
}
}
The attribute [PersonPage_json.Name]
is used to hint what is the path in JSON-by-example that the partial class refers to.
As you might have noticed, accessing a child object from a parent object in code-behind is as simple as providing a path expression: this.Name.FirstName = words[0]
. The child property (this.Name
) is of known type (PersonPageName
).
However, accessing a parent from a child requires casting (var person = this.Parent as PersonPage
). This is because there might be various parents that employ this particular child. In general, using the Parent
property is discouraged, because it breaks the single-direction data flow. Child should be controlled by the parent and not vice versa.
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