Legacy versus VB expressions

This section lists the common use cases for binding app elements, and how you can achieve the binding using legacy and VB expressions.

Using static string URLs in Image controls

Legacy	VB
Add the Image control. Set the URL/Value binding property to `https://path/to/the/image_file.jpg` Note: Base64 images are also supported.	Add the Image control. Set the Source property to `new AppsFile("https://path/to/the/image_file.jpg")` Note: Base64 images are also supported.

Using the File field of an entity in Image controls

Legacy	VB
In your app, reference the entity that holds the desired file. Bind the entity to a Table control. Add the Image control. Set the URL/Value binding property to the file.	In your app, reference the entity that holds the desired file. Bind the entity to a Table control. Add the Image control. Set the Source property to `MainPage.Table.SelectedItem.FileColumn`

Using files from a Storage Bucket in Image controls

Legacy	VB
In your app, reference the storage bucket that holds the desired file. Create an app variable of type AppsFile. For example `fileVar`. Add the Download file from Storage Bucket rule. Assign the downloaded file to the previously created app variable (`fileVar`). Add the Image control. Set the URL/Value binding property to `fileVar`.	In your app, reference the storage bucket that holds the desired file. Create an app variable of type AppsFile. For example `fileVar`. Add the Download file from Storage Bucket rule. Assign the downloaded file to the previously created app variable (`fileVar`). Add the Image control. Set the Source property to `fileVar`.

Using choice sets to populate List controls

Legacy	VB
Leverage entities in your app by using choice sets	In your app, reference the entity with the choice set. Add the List control. Set the List source property to `GetChoiceSet("entity_name")`. Set the Column property to the choice set name. Read this procedure for more information.

Referencing a choice set bound to List controls

Legacy	VB
Steps 4 and 5 in Leverage entities in your app by using choice sets	`<PAGE_NAME>.<CONTROL_NAME>.SelectedItem.<COLUMN_NAME>`<PAGE_NAME>.<CONTROL_NAME>.SelectedItem.<COLUMN_NAME>

Setting a single select choice set as the default value for controls

Dropdown, Radio Button and List controls support single select choice sets.

Legacy	VB
	`MainPage.Dropdown.DataSource.data.Select(Function(x) x.NumberId).ToList(0)`MainPage.Dropdown.DataSource.data.Select(Function(x) x.NumberId).ToList(0)

Setting a multiselect choice sets as the default value for controls

Multiselect Dropdown controls support multiselect choice sets.

Legacy	VB
	`<PAGE_NAME>.<MULTISELECT_CONTROL_NAME>.DataSource.data.Where(Function(x) <VARIABLENAME>.<ENTITY_FIELD_OF_TYPE_CS>.contains(x.NumberId)).toList()`<PAGE_NAME>.<MULTISELECT_CONTROL_NAME>.DataSource.data.Where(Function(x) <VARIABLENAME>.<ENTITY_FIELD_OF_TYPE_CS>.contains(x.NumberId)).toList() Note: To use this expression, ensure the entity variable is set to `selectedItem` using a Set Value rule.

Legacy

<PAGE_NAME>.<MULTISELECT_CONTROL_NAME>.DataSource.data.Where(Function(x) <VARIABLENAME>.<ENTITY_FIELD_OF_TYPE_CS>.contains(x.NumberId)).toList()<PAGE_NAME>.<MULTISELECT_CONTROL_NAME>.DataSource.data.Where(Function(x) <VARIABLENAME>.<ENTITY_FIELD_OF_TYPE_CS>.contains(x.NumberId)).toList()

Note:

To use this expression, ensure the entity variable is set to selectedItem using a Set Value rule.

Using static strings to populate List controls

Legacy	VB
`=["Value1", "Value2", "Value3"]`=["Value1", "Value2", "Value3"]	`AppsDataSource.from({"Value1", "Value2", "Value3"})`AppsDataSource.from({"Value1", "Value2", "Value3"})

Bind a date to Date Picker controls

Legacy	VB
To bind todays date, set the Default Date property to `=Now()`	To bind todays date, set the Default Date property to `DateOnly.FromDateTime(Now)`
To bind a specific date, for example 5th May 2021, set the Default Date property to `2021-01-05`	To bind a specific date, for example 5th May 2021, set the Default Date property to `new DateOnly(2021,1,25)`

Using an entity Date-Time field in Date Picker controls

Legacy	VB
Bind the required entity field to the Date Picker control.	`DateOnly.FromDateTime(customerEntityVar.DOB.Value.Date)`DateOnly.FromDateTime(customerEntityVar.DOB.Value.Date)

Computing the difference between two Date Picker values

Legacy	VB
N/A	`MainPage.Datepicker1.Value.Value.DayNumber - MainPage.Datepicker.Value.Value.DayNumber`MainPage.Datepicker1.Value.Value.DayNumber - MainPage.Datepicker.Value.Value.DayNumber

Referencing errors

You can reference the errors from the following rules:

Start Process
Entity rules
Queue rules
Trigger Workflow rule

Legacy	VB
Start Process rule: Handling Errors	In VB expressions, errors are exposed in the rule output. Reference an error as follows: `<PAGENAME>.<RULENAME>.Error.Message`<PAGENAME>.<RULENAME>.Error.Message `<PAGENAME>.<CONTROLNAME>.<RULENAME>.Error.Message`<PAGENAME>.<CONTROLNAME>.<RULENAME>.Error.Message