Simple Xamarin.iOS application for opening files with custom extension.

A_sample-open-file-ios-app.md

...

https://developer.apple.com/library/archive/qa/qa1587/_index.html

https://developer.apple.com/library/archive/documentation/FileManagement/Conceptual/understanding_utis/understand_utis_declare/understand_utis_declare.html#//apple_ref/doc/uid/TP40001319-CH204-SW1

https://developer.apple.com/library/archive/documentation/Miscellaneous/Reference/UTIRef/Articles/System-DeclaredUniformTypeIdentifiers.html#//apple_ref/doc/uid/TP40009259

AppDelegate.cs

using System;
using System.IO;
using Foundation;
using UIKit;

namespace PocOpenFileiOS
{
    [Register(nameof(AppDelegate))]
    public class AppDelegate : UIApplicationDelegate
    {
        // ...
       
        public override bool OpenUrl(UIApplication app, NSUrl url, NSDictionary options)
        {

            if (url != null && url.IsFileUrl)
            {
                // TODO: check file extension
                
                var a = NSData.FromUrl(url);

                var documents = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
                var filename = Path.Combine(documents, "new_file.4321c");

                if (a.Save(filename, true, out _))
                {
                    //var data = File.ReadAllText(filename);
                    
                    
                }

                return true;
            }

            return false;
        }
    }
}

Info.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>CFBundleDisplayName</key>
	<string>PocOpenFileiOS</string>
	<key>CFBundleIdentifier</key>
	<string>name.pakalo.evgeniy.PocOpenFileiOS11</string>
	<key>CFBundleShortVersionString</key>
	<string>1.0</string>
	<key>CFBundleVersion</key>
	<string>1.0</string>
	<key>LSRequiresIPhoneOS</key>
	<true/>
	<key>MinimumOSVersion</key>
	<string>13.2</string>
	<key>UIDeviceFamily</key>
	<array>
		<integer>1</integer>
		<integer>2</integer>
	</array>
	<key>UILaunchStoryboardName</key>
	<string>LaunchScreen</string>
	<key>UIMainStoryboardFile</key>
	<string>Main</string>
	<key>UIMainStoryboardFile~ipad</key>
	<string>Main</string>
	<key>UIRequiredDeviceCapabilities</key>
	<array>
		<string>armv7</string>
	</array>
	<key>UISupportedInterfaceOrientations</key>
	<array>
		<string>UIInterfaceOrientationPortrait</string>
		<string>UIInterfaceOrientationLandscapeLeft</string>
		<string>UIInterfaceOrientationLandscapeRight</string>
	</array>
	<key>UISupportedInterfaceOrientations~ipad</key>
	<array>
		<string>UIInterfaceOrientationPortrait</string>
		<string>UIInterfaceOrientationPortraitUpsideDown</string>
		<string>UIInterfaceOrientationLandscapeLeft</string>
		<string>UIInterfaceOrientationLandscapeRight</string>
	</array>
	<key>XSAppIconAssets</key>
	<string>Assets.xcassets/AppIcon.appiconset</string>
	<key>CFBundleName</key>
	<string>PocOpenFileiOS</string>
	<key>CFBundleDocumentTypes</key>
	<array>
		<dict>
			<key>CFBundleTypeName</key>
			<string>Client certificate</string>
			<key>CFBundleTypeIconFiles</key>
			<array>
				<string>Icon-App-29x29@2x</string>
			</array>
			<key>LSItemContentTypes</key>
			<array>
				<string>name.pakalo.evgeniy.PocOpenFileiOS11.c1234</string>
			</array>
		</dict>
	</array>
	<key>UTExportedTypeDeclarations</key>
	<array>
	    <dict>
	        <key>UTTypeDescription</key>
	        <string>XDXF - XML Dictionary eXchange Format</string>
	        <key>UTTypeConformsTo</key>
	        <array>
	            <string>public.text</string>
	        </array>
	        <key>UTTypeIdentifier</key>
	        <string>name.pakalo.evgeniy.PocOpenFileiOS11.c1234</string>
	        <key>UTTypeTagSpecification</key>
	        <dict>
	            <key>public.filename-extension</key>
		    <array>
                        <string>c1234</string>
                    </array>
	            <key>public.mime-type</key>
	            <string>text/xml</string>
	        </dict>
	    </dict>
	</array>
</dict>
</plist>

More resources: https://www.raywenderlich.com/3109-email-tutorial-for-ios-how-to-import-and-export-app-data-via-email-in-your-ios-app