UIAppearance appearanceWhenContainedInInstancesOfClasses incorrectly restricted to tvOS

[sushihangover]

Note: This is a C/P from my StackOverflow answer, so if you need additional info, just ask, thanks.

• https://stackoverflow.com/questions/48262588/xamarin-ios-uiapperance-setdefaulttextattributes

There are a number of missing UIAppearance features in Xamarin.iOS and in regards to your question, there is a missing API.

• This is a bug, 🍣 I wrote my own UIAppearance.cs to add the missing features and correct the missing API and assume no other Xamarin.iOS coders really use the newer UIAppearance features as it has been broken since iOS 9 in Xamarin.

First, appearanceWhenContainedIn is deprecated and you should be using appearanceWhenContainedInInstancesOfClasses instead.

AppearanceWhenContainedIn - was deprecated in iOS 9 and is not recommended for use.

Second, appearanceWhenContainedInInstancesOfClasses is incorrectly defined within Xamarin.iOS as only available in tvOS via a #if TVOS and that is just not true.

Re: Apple Docs: https://developer.apple.com/documentation/uikit/uiappearance/1615013-appearancewhencontainedininstanc

#if TVOS
   // new in iOS9 but the only option for tvOS
   const string selAppearanceWhenContainedInInstancesOfClasses = "appearanceWhenContainedInInstancesOfClasses:";
   ~~~

UIAppearance.cs#L77

Thus it is not available via the iOS wrapper API, but of course is available directly from the ObjC runtime as such:

var NSForegroundColorAttributeName = Dlfcn.GetStringConstant(UIKitLibraryHandle, "NSForegroundColorAttributeName");
var defaultAttributes = NSDictionary.FromObjectsAndKeys(new NSObject[] { UIColor.Red }, new NSObject[] { NSForegroundColorAttributeName });
var styleHandle = GetAppearanceEx(Class.GetHandle("UITextField"), typeof(UISearchBar));
void_objc_msgSend_IntPtr(styleHandle, Selector.GetHandle("setDefaultTextAttributes:"), defaultAttributes.Handle);
var searchBar = new UISearchBar(new CGRect(0, 50, 300, 40));
searchBar.Placeholder = "Xamarin.iOS";
Add(searchBar);

The next problem there are a number of Xamarin.iOS methods marked internal that are needed for the above code to function, so some copy/paste/modify of some source is needed:

public const string selAppearanceWhenContainedInInstancesOfClasses = "appearanceWhenContainedInInstancesOfClasses:";

public static readonly IntPtr UIKitLibraryHandle = Dlfcn.dlopen("/System/Library/Frameworks/UIKit.framework/UIKit", 0);

[DllImport("/usr/lib/libobjc.dylib", EntryPoint = "objc_msgSend")]
public static extern IntPtr IntPtr_objc_msgSend_IntPtr(IntPtr receiver, IntPtr selector, IntPtr arg1);

[DllImport("/usr/lib/libobjc.dylib", EntryPoint = "objc_msgSend")]
public static extern void void_objc_msgSend_IntPtr(IntPtr receiver, IntPtr selector, IntPtr arg1);

public static IntPtr GetAppearanceEx(IntPtr class_ptr, params Type[] whenFoundIn)
{
	var ptrs = TypesToPointers(whenFoundIn);
	var handles = NSArray.FromIntPtrs(ptrs);
	using (var array = handles)
	{
		return IntPtr_objc_msgSend_IntPtr(class_ptr, Selector.GetHandle(selAppearanceWhenContainedInInstancesOfClasses), array.Handle);
	}
}

public static IntPtr[] TypesToPointers(Type[] whenFoundIn)
{
	IntPtr[] ptrs = new IntPtr[whenFoundIn.Length];

	for (int i = 0; i < whenFoundIn.Length; i++)
	{
		if (whenFoundIn[i] == null)
			throw new ArgumentException(String.Format("Parameter {0} was null, must specify a valid type", i));
		if (!typeof(NSObject).IsAssignableFrom(whenFoundIn[i]))
			throw new ArgumentException(String.Format("Type {0} does not derive from NSObject", whenFoundIn[i]));

		var classHandle = Class.GetHandle(whenFoundIn[i]);
		if (classHandle == IntPtr.Zero)
			throw new ArgumentException(string.Format("Could not find the Objective-C class for {0}", whenFoundIn[i].FullName));
		ptrs[i] = classHandle;
	}
	return ptrs;
}

Xamarin.iOS Version: 11.8.0.1

[justin-caldicott]

Hmm, seems like a bug that there are no bindings for this for iOS. Any plans to fix it? It's been two years. :)

[tipa]

would love to see this fixed as well!

[amirvenus]

Hmm, seems like a bug that there are no bindings for this for iOS. Any plans to fix it? It's been two years. :)

Soon 4 years and it hasn't been fixed. How lovely!