Microsoft Power Apps Canvas Apps, Power Fx Formulas, and Controls
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Some dates can't be in the future: the day a shift was worked, a delivery that has arrived, an accident that has happened. Set the modern date picker's EndDate to Today(), and its calendar greys out every day after today.
The modern Power Apps date picker's built-in formats follow the language the app runs in, so the same date can read differently from one person to the next. For an app used in the UK, set Format to the pattern "dd/mm/yyyy" so every date reads day first, and set StartOfWeek to Monday so the calendar matches a UK week.
When an app needs a date, give people a calendar instead of a text box. The modern Date picker control shows one: insert it, start it on today with DefaultDate, and read the date people choose from SelectedDate.
A formula checked IsEmpty(cmbEndLO.SelectedItems) to see whether a modern combo box had a choice yet. With nothing chosen, it still returned false, so the formula carried on with a blank value and showed 2 hours for a shift with no finish time. IsBlank(cmbEndLO.Selected) is the check Microsoft documents for "nothing selected", and it works.
The app gets its first real screen in this part. The Home screen greets the signed-in person, shows their department and, if they approve overtime, which departments they approve for. Its tiles depend on the person's role: everyone can log overtime, but only approvers, payroll staff and admins see the screens meant for them.
A horizontal container lines its controls up in a row. On a wide screen that's what you want; on a phone, the row is wider than the screen and the last controls are cut off or disappear. The container's Wrap property moves the controls that don't fit onto the next row, and one formula makes them full width on phones.
A SharePoint list often names people in a Person column: a department's approvers, a project's owners, a request's reviewers. A canvas app can find the items that include the signed-in person by comparing their email with the column's Email values. With a column that allows several people, it takes one extra step to keep SharePoint's delegation rules happy.
Apps often show different things to different people: reports for payroll staff, a settings screen for admins. When those people are in Microsoft Entra security groups, a canvas app can ask the Office 365 Groups connector who's in a group and check whether the signed-in person is one of them. One named formula per group does it.
The Office 365 Groups connector lets a canvas app read and manage the groups in your organization, including who is in a group. Despite its name, it lists the members of security groups too. It's a standard connector, and adding it takes a minute from Studio's Data pane.
Some values an app needs are different for every organization that installs it, such as the IDs of its security groups. Typed into formulas, they would have to be changed inside the app each time. A small SharePoint list of settings keeps them outside the app, where a site owner can change them and the app looks them up by name.
