Need details regarding SCRIPT- PHASES (Always,Render,Update,Validate and Process)

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n/A

postedon May 6, 2013at 3:54 PM

Was Trying to set a particular value in a dropdown-list as the default selected one based on some condition. Have added a Script in the screen to add the logic and have set it to 'Update' Phase,but was finding that the script logic was not getting executed and thats why the value which I was trying to set as the default value of the drop-down is not getting set, I found that whenever Iam changing the PHASE to say 'RENDER' or 'ALWAYS' my script is getting called and it is setting the default value properly, but the problem with these phases(RENDER,ALWAYS) is that every time I am trying to change the default value of the dropdown to say some other values, the script seems to be running every time on change of the drop-down values and setting the value back to the default one that was set in the SCRIPT component. Need to know which phase should i use in my script function so that initially it sets some required default dropdown value but later user can have the ability to change it to some other value, details regarding different phases and when one should use which one would also help immensley.

Stephan

repliedon May 6, 2013at 4:45 PM

Hi K Das,

If you bind your drop-down list to a variable of type "String", you could treat the value null as a flag for "not initialized". You could then use a Script component which executes the following code in the Render phase:

1// if variable has not been initialized yet ...
2If $variable == null Then
3   // set default value depending on some logic
4   If SomeLogic() Then
5      $variable := 'EUR';
6   Else
7      $variable := 'USD';
8   End
9Else
10   // keep current value
11End

This piece of script code is still execute whenever the screen is rendered, but it has an effect on the variable only the very first time (assuming that the variable has the value null then). If your variable is of type Integer or Long, you could use an other value like "0" or "-1" as marker for "not initialized".

Another solution could be to set the variable's default value in a Script Task in the process, immediately before the Screen Task for the screen which contains the drop-down list.

Stephan

repliedon May 6, 2013at 5:20 PM

Some more information about screen phases ...

There are four screen phases: Render, Update, Validate and Process

The first screen phase Render is the phase where screen components generate their HTML code. This phase is executed when Appway has to show the content of a screen to a user. The "output" of this phase is the HTML code which has to be sent back to the client. If you execute script code in this phase, it may have an impact on the output presented to the user. I write "may" because it depends on where you place the code. Components in a screen are rendered (executed) top-down. If you add a Script component at the top of your screen and you change a variable value there, all other components will see the changed value when they have to render their own HTML code. If you however put the Script component at the end of the screen, all the components above will first get rendered based on the old value of the variable, before the variable is changed near the end of the Render phase.

At the end of the Render phase, Appway does some post-processing with the HTML code and then sends it to the client. The post-processing includes translation of language labels like "[ LABEL:button.next ]" and replacement of placeholders like "{ CONTEXT_PATH }".

The other three screen phases Update, Validate and Process are executed after the user has submitted the page back to Appway. A submit is made whenever the user triggers an event which has an attached server-side action (e.g. clicking on a Button component with a Script Action attached to the button's "onclick" event).

The Update phase is used to store all the input values in the variables and properties bound to the controls (input elements). If you have a text field bound to the expression "$person.name", Appway stores the input value in the property "name" of the data object referenced by the variable "$person". All bindings are executed top-down. The top-most control on the screen is the first for which the input value is stored first.

During the Validate phase Appway checks the validation rules attached to the controls. Again, the first control on the screen is the first to get validated. From there, Appway works its way down through the screen and validates every control it finds. If there is a validation error for a control, Appway remembers this error in order to show it to the user when the screen gets rendered the next time.
Side note: The Validate phase is however not the only phase in which validation errors could occur. If a control is bound to a variable or property of type "Integer" or "Date", the value entered by the user has to be converted in this target type in order to get stored during the Update phase. If the user enters "abc" into a text field bound to a variable of type "Integer", Appway cannot convert this value into an Integer. As a result, a conversion error is generated. Such an error is treated by Appway like a validation error occurring during the Validation phase.

The Process phase finally is usually used to execute server-side actions triggered by events. Appway once again goes through all components in the screen and checks for every component if any events have been triggered for it. If yes, the associated actions are executed.
Side node: By default, actions get executed only if there are no validation errors. This prevents the execution of business logic like sending an email to your client even though not all required information has been entered. You can override this behavior by setting the "Ignore Errors" property on the server-side action.

If you add a Script component to your screen and pick one of the phases Update, Validate or Process, this code gets executed when Appway finds this component while traveling through the component tree in the given phase. If you set the phase to "Always", the code gets executed in every phase. You can control whether the code should get executed early or late in the phase by adding the component at the beginning or end of your screen.

Does this information help you?

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