HTML Checkbox behaviour

Forum > Business Object Composition > HTML Checkbox behaviour

Thomas Schaer

postedon February 28, 2013at 5:35 PM

Can an HTML Checkbox (not a Checkbox) only be bound to a boolean? If so, how should it behave according to the implementation: Will the property "checked" set the bound variable automatically to true or will this be overridden by any default expression in the variable assignments?

Stephan

repliedon March 1, 2013at 11:32 AM

You can "bind" an HTML Checkbox component to almost any type of variable. You only have to make sure that the value of the property "Value" can be converted into a value of this type. In most cases, you probably want to use an assigned variable of type Boolean. You then set the "Name" property to the name of the assigned variable (without '$' sign) and the "Value" property to "true". If the checkbox is then checked at the time the form is submitted, the browser will send an HTTP parameter with the name of the variable and the value "true" to the server. Appway will then try to convert the parameter value into a Boolean (because this is the type of the assigned variable) and assign the value to the variable. If the checkbox is not checked, the browser does not submit an HTTP parameter for this checkbox at all. The assigned variable will therefore get initialized with its default value/expression.

But you can also use a variable of type Integer, String, Date etc. If the checkbox is checked, the value you set for the property "Value" is sent to the server, converted into the variable's type and assigned to the variable. If the checkbox is not checked, no value is sent to the server and the variable gets its default value (according to the variable definition).

The property "Checked" is a static property. If you enable it, the checkbox will be checked by default. If you leave it disabled, the checkbox will not be checked by default. There is no hidden logic behind that. Nothing that would link the state of the checkbox to a variable or expression. I thing we should make the "Checked" property a dynamic property in the next Appway version. That would allow you to specify an expression which returns true or false, depending on whether the checkbox should be checked or not by default. For now, there are two workarounds:
1. You put two HTML Checkbox components on your screen, one where "Checked" is enabled and one where it is disabled. You use an If and an Else component to decide which component to show depending on the current value of you variable.
2. You give the HTML Checkbox component an HTML id and emit some JavaScript code which gets executed on-load of the page and sets the checkbox' state as desired.

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