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Picker Attribute "SelectedIndex" Not being respected on page load on Android?
Description
I have a Picker that is attached to an enum for a "list type" property, with a "SelectedIndex=0" attribute on the picker, which I believe means that I want that index of the enum to be selected first, as a 'default'. This works great on the windows app, but when running on Android, the picker control is empty. Then, I'm able to force something into the control by manually changing the "selected index" in the .xaml from say, 0 to 1, which I think then triggers the event, and updates in the app. But obviously since I think the point of SelectedIndex is to default something in, then, well, it should default something in.
I found a workaround for this by grabbing the picker control in the constructor in the code-behind for the page, and setting it's SelectedIndex property there, which fixes it. But I presume that the xaml property should work without needing to do that.
Here is the repo for the demo app i'm playing with -
Xaml for the view with the Picker - https://github.com/Programming-With-Chris/ShoppingList/blob/master/ShoppingList/View/UserListDataInput.xaml
Code Behind showing the 'work around' - https://github.com/Programming-With-Chris/ShoppingList/blob/master/ShoppingList/View/UserListDataInput.xaml.cs
Steps to Reproduce
- Use Picker Control in a ContentPage
- Set the "SelectedIndex="0"" value on the Picker
- See that on that page loading, nothing is populated on Android, but is on the Windows App
Version with bug
6.0.408 (current)
Last version that worked well
Unknown/Other
Affected platforms
Android
Affected platform versions
'android'">21.0</SupportedOSPlatformVersion>
Did you find any workaround?
Yes, as described above - "I found a workaround for this by grabbing the picker control in the constructor in the code-behind for the page, and setting it's SelectedIndex property there, which fixes it. "
Relevant log output
No response
Edit: Can confirm that this happens on iOS. Will check Windows and Mac tomorrow.
Investigated this for a few hours. It seems that in XamlNode.cs the properties of Picker have SelectedIndex above the Binding PickerItems.
It first then iterates into SelectedIndex, eventually it comes in BindableObject.cs in SetValueCore, where property.CoerceValue is executed against the selectedIndex from the xaml (1 in my example). It is coerced to -1 because there are no items yet, and after that it is not loaded from the XamlNode again.
The next property after SelectedIndex is the PickerItems Binding.
I have yet to figure out what determines the order in which properties are listed, so that I can change the behavior. As seen in the screenshot other properties x:name and textColor are applied after the Binding PickerItems.
Reproduced the issue on Android, iOS, Windows and Mac Catalyst. Labels of issue can be updated. Also ideas about solution direction are welcome. @jfversluis
Edit: Also tested this in Xamarin Forms, and this issue is also reproducible there. Is this perhaps intended behavior or should an issue be created in Xamarin Forms github as well?
Verified this on Visual Studio Enterprise 17.7.0 Preview 1.0. Repro on Windows 11, Android 13.0 and iOS 16.4 with below Project: 9150.zip
Frighteningly, more than a year now and nothing, yikes. In case anyone is still interested, this is still going on. In fact, I can't even set the SelectedIndex in the page's constructor as a work-around. The default value is -1 and even after an explicit setting of the value, it does not change.
~This is fixed in a preview of MAUI 8 https://github.com/dotnet/maui/pull/16387 Sadly, this is not backported to a service release of MAUI 7.~
You're right, this still isn't fixed. The workaround is to use SelectedItem and convert it back to an index in your VM.
(Added labels per https://github.com/dotnet/maui/issues/9150#issuecomment-1219386418 comment)
Is this ever getting fixed, its getting annoying how long this has been open and the sad part is this is a control which is used ALOT
