Events (O'Caml)

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Events

Events (O'Caml)

The representation of events in O'Caml

In the module Wd_types, the event type is defined as follows:

type event =
    Button of string
  | Image_button of (string * int * int)
  | Indexed_button of (string * string)
  | Indexed_image_button of (string * string * int * int)
  | No_event
  | Popup_request of string

The variants of the type correspond to the event types:

Button event: A button event for the button n is represented as
```
Button n
```
Indexed button event: A button event for the button n with index i is represented as
```
Indexed_button(n,i)
```
Imagebutton event: An imagebutton event for the button n is represented as
```
Image_button(n,x,y)
```
The coordinate (x,y) is the position of the click relative to the image.
Indexed imagebutton event: An imagebutton event for the button n with index i is represented as
```
Indexed_image_button(n,i,x,y)
```
The coordinate (x,y) is the position of the click relative to the image.
Hyperlink event: A hyperlink event for the anchor n is represented as
```
Button n
```
The representations for hyperlinks and for buttons are intentionally the same.
Indexed hyperlink event: A hyperlink event for the anchor n with index i is represented as
```
Indexed_button(n,i)
```
The representations for hyperlinks and for buttons are intentionally the same.
Popup request: A popup request is represented as
```
Popup_request s
```
Note that the current page is changed to the page popping up while the popup request is processed.
The parameter s of the popup request is the second argument of the generated open Javascript function (to simplify parameterized popup windows). For example, a popup window declared with
```
<ui:server-popup page="x"/>
```
can be opened by the Javascript statement
```
open_x(window_specification, s);
```
The parameter s is passed back to the application once the window pops up and the contents of the window are requested. You can use this parameter arbitrarily.
Popups are explained in conjunction with ui:server-popup.
Null event: The null event is represented as
```
No_event
```

Handling events

The handle method of the current dialog is called when the event has been triggered. The method event can be used to find out the last event, e.g.

  method handle =
    let e = self # event in
    match e with
      Button("this_button") ->
        ...
    | Button("that_button") ->
        ...
    | Indexed_image_button("clicked_icon", x, y) ->
        ...
    | _ ->
        (* It is recommended to do nothing as default *)
        ()

When the handle method returns normally, the current page of the current dialog is generated again. Alternatively, another page can be set by raising the exception Change_page; or it can be changed to another dialog instance by raising the exception Change_dialog. Example:

   method handle =
    let e = self # event in
    match e with
      Button("this_button") ->
        self # set_variable "xy" (String_value "wow");
        (* ... and continue with the same page *)
    | Button("that_button") ->
        self # set_variable "xy" (String_value "boo");
        raise(Change_page "another_page")
    | Indexed_image_button("clicked_icon", x, y) ->
        let next_dlg =
           self # universe # create (self#environment) "other_dialog" in
        raise(Change_dialog next_dlg)