Question

我们正在尝试使用Xamarin.iOS中的扩展为UIAlertController设置AutomationId。但是在GetAccessibilityIdentifier方法下，应用程序在var valuePtr = objc_getAssociatedObject(alertAction.Handle, DescriptiveName.Handle);处不一致地崩溃了。也不知道为什么会崩溃。

以下是代码示例：

public static class UIAlertControllerExtension
    {
        public static void ApplyAccessibilityIdentifiers(this UIAlertController alertController)
        {
            foreach (var action in alertController.Actions)
            {
                var lable = action.ValueForKey((NSString)"__representer");
                var view = lable as UIView;
                view.AccessibilityIdentifier = action.GetAccessibilityIdentifier();
            }
        }
    }

    public static class UIAlertActionExtension
    {

        private static readonly NSString DescriptiveName = new NSString("AccesabilityIdentifier" + nameof(UIAlertActionExtension));

        #region "Extension properties"

        enum AssociationPolicy
        {
            Assign = 0,
            RetainNonAtomic = 1,
            CopyNonAtomic = 3,
            Retain = 01401,
            Copy = 01403,
        }

        [DllImport("/usr/lib/libobjc.dylib")]
        static extern void objc_setAssociatedObject(
            IntPtr pointer, IntPtr key,
            IntPtr value, AssociationPolicy policy);

        [DllImport("/usr/lib/libobjc.dylib")]
        static extern IntPtr objc_getAssociatedObject(
            IntPtr pointer, IntPtr key);


        #endregion

        public static void SetAccessibilityIdentifier(this UIAlertAction alertAction, NSString accessabilityIdentifier)
        {
            objc_setAssociatedObject (alertAction.Handle, DescriptiveName.Handle, accessabilityIdentifier.Handle, AssociationPolicy.Retain);
        }

        public static NSString GetAccessibilityIdentifier(this UIAlertAction alertAction)
        {
            try
            {
                var valuePtr = objc_getAssociatedObject(alertAction.Handle, DescriptiveName.Handle); // App is crashed at this line.
                if (valuePtr != IntPtr.Zero)
                {
                    var result = ObjCRuntime.Runtime.GetNSObject(valuePtr);
                    if (result != null)
                        return (NSString)result;
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }

            //var value = ObjCRuntime.Runtime.GetNSObject(valuePtr) as NSString;
            return new NSString("");
        }

    }

使用上述扩展方法创建警报控制器并设置AutomationId。

private void ShowAlert()
{
    var alertController = UIAlertController.Create("Title", "Message", UIAlertControllerStyle.Alert);

    var action = UIAlertAction.Create("Ok", UIAlertActionStyle.Default, delegate
                {

                    // Do Somthing

                });

   action.SetAccessibilityIdentifier((NSString) accessibilityIdentifier);

   alertController.AddAction(action);

   this.PresentViewController(alertController, true, () => { alertController.ApplyAccessibilityIdentifiers(); });
}

我们从视图控制器的按钮单击调用此方法，它可以正常工作几次。但是当第三次或第四次显示警报时，应用程序正在崩溃。

请帮我解决此问题。

提前致谢。

Answer 1

AssociationPolicy.Retain可能会在意外时间发布此属性，因此您的应用会崩溃。您可以将其更改为AssociationPolicy.RetainNonAtomic。 NonAtomic将使您的应用程序平稳，快速地运行。

如果您只想存储字符串并在以后使用它。为什么不试试NSUserDefaults或静态实例？

Xamarin iOS App在使用AssociatedObject为UIAlertController设置AutomationId时崩溃 - objc_getAssociatedObject

1 个答案: