The Use of Formulas in Collections & Callback Commands

When you use collections with a member method that needs a callback method, many of you have asked us for a more straightforward way.

You asked; we delivered!

Starting with 4D v19 R6, 4D allows you to use a formula to define a callback in the collection member functions, the EXECUTE METHOD IN SUBFORM, CALL FORM, and CALL WORKER commands. If you can reduce your code to a simple expression, you can pass it directly into the formula without using a method. 

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Change the properties of several methods at once by code

We know that sometimes you want to change the properties of multiple methods without having to open the property dialog for each method.

For example, you want to set all methods to “Can be run in preemptive mode” status, then compile your database. So with compilation errors, you get an overview of the methods to modify to be preemptive.

Using the METHOD GET NAMES command to retrieve the list of methods from your database, and then using the METHOD SET ATTRIBUTES command to modify the attributes, lets you modify them all at the same time!

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How to display a multilevel collection in different list boxes!

Starting with 4D v17, the content of a multilevel collection can easily be displayed in different list boxes. Meaning that you can bind several list boxes to display nested details … without a single line of code! This can be achieved by simply using an object or a collection as the data source for another list box!

With the new list box collection type, the “Current item” and “Selected items” properties have been added. Keep in mind that the “Current item” property allows you to get an object, while the “Selected item” property returns a collection.

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Loops, loops and … more loops!

Like many other programming languages, 4D provides the ability to iterate over numbers with a For(…) / End for statement, or over a condition thanks to the While(…)/End while and Repeat/Until(…) keywords. These iterations (or loops) are very useful, but not the most appropriate way to iterate over advanced data types such as collections and entity selections. That’s why the new For each(…)/End for each iterator has been created, to help ease your coding!

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Query collections

Simplicity is the ultimate sophistication, and with over 40 methods in 4D v16 R6 to manage collections, things are getting much easier for you as a developer. Not only is your code clean and more readable, but its also written in record time!

In this blog post we’ll take a look at how the two new methods, query and indices, will allow you to manipulate and retrieve items from a collection in a snap!