android - Xamarin.Forms 中未调用 OnOptionsItemSelected

Question

我是 Xamarin.Forms 的新手。我试图在单击 NavigationBar 后退按钮 时显示 DisplayAlert()。我已经尝试根据 this article 实现.问题是当我点击按钮时弹出窗口没有出现。我在 OnOptionsItemSelected() 方法上放置了一个断点，以查看它是否被调用，它没有。这是我的 MainActivity.cs

protected override void OnCreate(Bundle bundle)
{ 
    TabLayoutResource = Resource.Layout.Tabbar;
    ToolbarResource = Resource.Layout.Toolbar;

    base.OnCreate(bundle);

    global::Xamarin.Forms.Forms.Init(this, bundle);
    global::Xamarin.FormsMaps.Init(this, bundle);
    LoadApplication(new App());

    Android.Support.V7.Widget.Toolbar toolbar = this.FindViewById<Android.Support.V7.Widget.Toolbar>(Resource.Id.toolbar);
    SetSupportActionBar(toolbar);
    
}

public override bool OnOptionsItemSelected(IMenuItem item)
{   
    //Placed a debugger here
    // check if the current item id is equals to the back button id
    if (item.ItemId == 16908332)
    {
        // retrieve the current xamarin forms page instance
        var currentpage = Xamarin.Forms.Application.Current.MainPage.Navigation.NavigationStack.LastOrDefault() as NavBackButtonContentPage;

        // check if the page has subscribed to the custom back button event
        if (currentpage?.CustomBackButtonAction != null)
        {
            // invoke the Custom back button action
            currentpage?.CustomBackButtonAction.Invoke();
            // and disable the default back button action
            return false;
        }

        // if its not subscribed then go ahead with the default back button action
        return base.OnOptionsItemSelected(item);
    }
    else
    {
        // since its not the back button click, pass the event to the base
        return base.OnOptionsItemSelected(item);
    }
}

我在 MasterDetailPage 中使用它。

Answer 1

isaman kumara 2019-06-01 的评论如下:

The issue will be fixed when you add following lines to MainActivity OnCreate method (after the LoadApplication(new App()); line)

Android.Support.V7.Widget.Toolbar toolbar = this.FindViewById<Android.Support.V7.Widget.Toolbar>(Resource.Id.toolbar); SetSupportActionBar(toolbar);

其中一个回复是这样说的:

This seems to no longer be working. SetSupportActionBar expects a parameter of type AndroidX.AppCompat.Widget.Toolbar and it won't work with Android.Support.V7.Widget.Toolbar.

通过在 LoadApplication 行之后将此添加到 MainActivity 的 OnCreate 方法，我能够让 OnOptionsItemSelected 在 Xamarin Forms 4.8 中再次工作:

if (FindViewById(Resource.Id.toolbar) is AndroidX.AppCompat.Widget.Toolbar toolbar)
{
    SetSupportActionBar(toolbar);
}

很抱歉没有直接评论之前的评论，但我没有足够的声望点数来这样做。