Microsoft Power Apps Canvas Apps, Power Fx Formulas, and Controls
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Patch fails with Network error when using Patch function: [YourList] ETAG mismatch. It isn't a network problem. The SharePoint item changed after your app read it, so SharePoint refused to overwrite the newer version. Catch it with IfError, tell the person what happened, and reload the item.
You rename a control in Tree view, and Power Apps stops you: Can't rename. This name is already being used. Please try a different name. Another control in the app already has that name, possibly on a different screen.
A control gets a red error icon, and its details say Unexpected characters. Characters are used in the formula in an unexpected way. Power Apps found a character it can't place in one of the control's formulas. In the example it was one closing bracket too many.
A gallery's OnSelect passes the selected row to another screen, and Power Apps marks it as an error: Incompatible type. We can't evaluate your formula because the context variable types are incompatible with the types of values in other places in your app. In the example, Self.Selected caused it, and ThisItem fixed it.
People open the Career Development Plan app to see what's expected of them. This part builds that screen: My plan lists the competencies for the person's job title, each with its level and a badge saying where their response stands. It also explains how the app asks SharePoint for exactly those items, and nothing more.
Most real conditions have more than one part: this job title and still active, not loading and nothing to show. And is true only when all parts are true; Or is true when any part is.
When a Power Apps formula filters a SharePoint list, there are two ways it can run. Either SharePoint does the filtering and sends back only the matching items, or Power Apps downloads some items and filters them itself. The first is delegation, and it's the only way that works on a big list.
Formulas often need a property of the control they're on, or of the control that holds it. Self is the current control and Parent is its container, so you don't have to type control names, and the formula still works when you copy the control or rename it.
An empty gallery is just blank space: people can't tell whether the app is broken, still loading, or has nothing to show. Put a message in its place that says why it's empty, and what happens next.
While a screen loads its data, show that something is happening. The modern Spinner control is a spinning ring with an optional label; make it visible only while a loading variable is true.
