Xamarin Forms Share Extension同步NSUserDefaults值失败及相关问题求助

我正在实现Xamarin Forms的Share Extension，让我的应用能接收其他应用发来的Zip文件。已经在Apple开发者账号中配置好App Group，也能获取到文件的共享URL，但通过NSUserDefaults将文件信息同步回容器应用时遇到了问题。

（注：Xamarin Forms的扩展应用无法调试，所以我给代码加了日志语句）

扩展应用代码 #

internal class CodeBasedViewController : SLComposeServiceViewController
{
    public override async void DidSelectPost()
    {
        int count = 0;
        try
        {
            NSExtensionItem item = ExtensionContext.InputItems[0];

            foreach(NSItemProvider prov in item.Attachments)
            {
                Log(count++.ToString());
                if (prov.HasItemConformingTo(UTType.URL) == true)
                {
                    Log("url type ok");

                    //Load item with Load Completion action
                    prov.LoadItem(UTType.URL, null, async (dataRaw, error) =>
                    {
                        Log("load url item ok");

                        //dataRaw是类似这样的路径："file:///Users/appname/Library/Developer/CoreSimulator/Devices/..GUID1../data/Containers/Shared/AppGroup/...GUID2.../"
                        string uri = dataRaw.ToString();
                        Log2(uri);

                        NSUserDefaults shared = new NSUserDefaults(
                                    "group.com.companyname.appname.ShareExtension",
                                     NSUserDefaultsType.SuiteName);

                        shared.SetString(uri, "zipfile");
                        if (shared.Synchronize())
                        {
                            //同步成功，代码走到这里
                            Log("sync success");

                        }
                        else
                            Log("sync failed");
                            
                        
                        
                        //base.DidSelectPost();

                    });

                }
            }
        }
        catch (Exception e)
        {
            Log("ex: " + e.Message);
        }

    }
}

遇到的问题 #

• LoadItem的完成操作处理6KB文件耗时约7秒，时长过长；
• 取消注释base.DidSelectPost()后，点击“Post”时扩展会立即关闭，怀疑完成操作代码被跳过；
• 容器应用激活时读取NSUserDefaults，发现uri值未同步过来（我认为获取到该uri就能访问zip文件）。

容器应用读取代码 #

public override void OnActivated(UIApplication uiApplication)
{
    base.OnActivated(uiApplication);

    NSUserDefaults shared = new NSUserDefaults(
                "group.com.companyname.appname.ShareExtension",
                 NSUserDefaultsType.SuiteName);

    //ok = true
    bool ok = shared.Synchronize();

    //这里返回null!!
    string uri = shared.StringForKey("zipfile");

}

我已经在主机虚拟机中创建了和容器、扩展应用Bundle名称一致的XCode应用，同样配置了App Groups，但问题依然存在。以下是两个应用的Info.plist文件：

容器应用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>UIDeviceFamily</key>
    <array>
        <integer>1</integer>
        <integer>2</integer>
    </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>MinimumOSVersion</key>
    <string>8.0</string>
    <key>CFBundleDisplayName</key>
    <string>MyApp</string>
    <key>CFBundleIdentifier</key>
    <string>com.companyname.MyApp</string>
    <key>CFBundleVersion</key>
    <string>1.0</string>
    <key>CFBundleName</key>
    <string>MyApp</string>
    <key>XSAppIconAssets</key>
    <string>Assets.xcassets/AppIcon.appiconset</string>
    <key>UILaunchStoryboardName</key>
    <string>LaunchScreen</string>
    <key>UIViewControllerBasedStatusBarAppearance</key>
    <false/>
    <key>NSExtensionPointIdentifier</key>
    <string>com.apple.share-services</string>
</dict>
</plist>

扩展应用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>CFBundleDevelopmentRegion</key>
    <string>en</string>
    <key>CFBundleDisplayName</key>
    <string>MyApp ShareExtension</string>
    <key>CFBundleExecutable</key>
    <string>MyApp.iOS.ShareExtension</string>
    <key>CFBundleIdentifier</key>
    <string>com.companyname.MyApp.ShareExtension</string>
    <key>CFBundleInfoDictionaryVersion</key>
    <string>6.0</string>
    <key>CFBundleName</key>
    <string>com.your-company.MyApp.iOS.ShareExtension</string>
    <key>CFBundlePackageType</key>
    <string>XPC!</string>
    <key>CFBundleShortVersionString</key>
    <string>1.0</string>
    <key>CFBundleSignature</key>
    <string>????</string>
    <key>CFBundleVersion</key>
    <string>1</string>
    <key>MinimumOSVersion</key>
    <string>8.0</string>
    <key>NSExtension</key>
    <dict>
        <key>NSExtensionAttributes</key>
        <dict>
            <key>NSExtensionActivationRule</key>
            <dict>
                <key>NSExtensionActivationSupportsFileWithMaxCount</key>
                <integer>1</integer>
                <key>NSExtensionActivationSupportsImageWithMaxCount</key>
                <integer>1</integer>
                <key>NSExtensionActivationSupportsMovieWithMaxCount</key>
                <integer>0</integer>
                <key>NSExtensionActivationSupportsText</key>
                <true/>
                <key>NSExtensionActivationSupportsWebURLWithMaxCount</key>
                <integer>1</integer>
            </dict>
        </dict>
        <key>NSExtensionPrincipalClass</key>
        <string>CodeBasedViewController</string>
        <key>NSExtensionPointIdentifier</key>
        <string>com.apple.share-services</string>
    </dict>
</dict>
</plist>

内容的提问来源于stack exchange，提问作者jho