android - 如何在我的应用程序不崩溃的情况下传递 DialogInterface OnDismissListener？

Question

我的 Xamarin.Android 应用程序有一个关于 IDialogInterfaceOnDismissListener 的问题。

我的重现样本:

public enum ConfirmationResult
{
    Cancel,
    Yes,
    No
}

public interface IDialogService
{
    Task<ConfirmationResult> ConfirmAsync(string title, string message, string acceptText, string declineText);
}

public class DialogService : IDialogService
{
    class DismissDelegateListener : IDialogInterfaceOnDismissListener, IDialogInterfaceOnCancelListener
    {
        private Action _callback;

        public DismissDelegateListener()
        {

        }

        public DismissDelegateListener(Action callback)
        {
            _callback = callback;
        }

        public void Dispose()
        {
            _callback = null;
        }

        public IntPtr Handle { get; }

        public void OnCancel(IDialogInterface dialog)
        {
            _callback?.Invoke();
        }

        public void OnDismiss(IDialogInterface dialog)
        {
            _callback?.Invoke();
        }
    }

    private readonly WeakReference<Context> _activity;

    public DialogService(Context activity)
    {
        _activity = new WeakReference<Context>(activity);
    }

    public async Task<ConfirmationResult> ConfirmAsync(string title, string message, string acceptText, string declineText)
    {
        Context target;
        if (!_activity.TryGetTarget(out target))
            return ConfirmationResult.Cancel;

        TaskCompletionSource<ConfirmationResult> tcs = new TaskCompletionSource<ConfirmationResult>();

        var builder = new AlertDialog.Builder(target);
        var d = builder
            .SetTitle(title)
            .SetMessage(message)
            .SetPositiveButton(acceptText, (sender, args) =>
            {
                tcs.SetResult(ConfirmationResult.Yes);
                (sender as AlertDialog)?.Dispose();
            })
            .SetNegativeButton(declineText, (sender, args) =>
            {
                tcs.SetResult(ConfirmationResult.No);
                (sender as AlertDialog)?.Dispose();
            })
            // if this line is uncommented my application crashes once the dialog is opened
//              .SetOnCancelListener(new DismissDelegateListener(() => { tcs.SetResult(ConfirmationResult.Cancel); }))
            .Create();

        d.Show();

        return await tcs.Task;
    }
}

只要我调用 SetOnCancelListener，我的应用程序就会崩溃并显示错误消息 System.InvalidCastException: Specified cast is not valid.

对我来说，一切似乎都是正确的——我正在传递所请求接口(interface)的实现，而且我的实现也不是那么困难。

这个问题是否给任何人敲响了警钟？

Answer 1

从 Java.Lang.Object 派生是解决方案。

        class DismissDelegateListener : Java.Lang.Object, IDialogInterfaceOnDismissListener, IDialogInterfaceOnCancelListener
        //class DismissDelegateListener : IDialogInterfaceOnDismissListener, IDialogInterfaceOnCancelListener
        {
            private Action _callback;

            public DismissDelegateListener()
            {

            }

            public DismissDelegateListener(Action callback)
            {
                _callback = callback;
            }

            protected override void Dispose(bool disposing)
            {
                _callback = null;
                base.Dispose(disposing);
            }

            public void OnCancel(IDialogInterface dialog)
            {
                _callback?.Invoke();
            }

            public void OnDismiss(IDialogInterface dialog)
            {
                _callback?.Invoke();
            }
        }