Question

我和Xamarin一起工作，还是新手，但我遇到了一个问题，我觉得我不应该这样做。这是我的问题：

using System;
using Xamarin.Forms;

namespace DataBinding_Lists
{
public class App
{
    public static Page GetMainPage ()
    {   
        var listView = new ListView { RowHeight = 40 };
        listView.ItemsSource = new Person []
        {
            new Person { FirstName = "Abe", LastName = "Lincoln" },
            new Person { FirstName = "Groucho", LastName = "Marks" },
            new Person { FirstName = "Carl", LastName = "Marks" },
        };

        listView.ItemTemplate = new DataTemplate(typeof(TextCell));
        listView.ItemTemplate.SetBinding(TextCell.TextProperty, "FirstName");
        listView.ItemSelected += async (sender, e) => {
            await DisplayAlert ("Tapped!", e.SelectedItem + " was tapped.", "OK", "");
        };

        return new ContentPage { 
            Content = new StackLayout
            {
                Padding = new Thickness (5,20,5,5),
                Spacing = 10,
                Children = { listView }
            }
        };
    }

}

}

显然，我在另一个名为＆＃34; Person。＆＃34;这个类有两个属性：＆＃34; FirstName＆＃34;和＆＃34;姓氏。＆＃34;当我尝试在Xamarin中将所有这些放在一起时，我得到的错误是：＆＃34;名称＆＃39; DisplayAlert＆＃39;在当前上下文中不存在。＆＃34;

Answer 1

有两种方法可以解决这个问题，我倾向于第二种方法。接近Edward L.所说的。

DisplayAlert是Xamarin.Forms页面上的一个方法...并且你在一个返回该页面的静态方法内部，所以你没有引用它。

所以你可以这样做：

using System;
using Xamarin.Forms;

namespace DataBinding_Lists
{
public class App
{
    private static Page page;
    public static Page GetMainPage ()
    {   
        var listView = new ListView { RowHeight = 40 };
        listView.ItemsSource = new Person []
        {
            new Person { FirstName = "Abe", LastName = "Lincoln" },
            new Person { FirstName = "Groucho", LastName = "Marks" },
            new Person { FirstName = "Carl", LastName = "Marks" },
        };

        listView.ItemTemplate = new DataTemplate(typeof(TextCell));
        listView.ItemTemplate.SetBinding(TextCell.TextProperty, "FirstName");
        listView.ItemSelected += async (sender, e) => {
            await page.DisplayAlert ("Tapped!", e.SelectedItem + " was tapped.", "OK", "");
        };

        page = new ContentPage { 
            Content = new StackLayout
            {
                Padding = new Thickness (5,20,5,5),
                Spacing = 10,
                Children = { listView }
            }

        };
        return page;
    }

}
}

你应该做的是创建一个新的类作为你的页面。

你的App.cs变成了这个：

using System;
using Xamarin.Forms;

namespace DataBinding_Lists
{
public class App
{
    public static Page GetMainPage ()
    {   
        return new PeoplePage();
    }

}
}

然后创建一个继承自Page的新类：使用系统; 使用Xamarin.Forms;

namespace DataBinding_Lists
{
public class PeoplePage : Page
{
    public PeoplePage()
    {   
        var listView = new ListView { RowHeight = 40 };
        listView.ItemsSource = new Person []
        {
            new Person { FirstName = "Abe", LastName = "Lincoln" },
            new Person { FirstName = "Groucho", LastName = "Marks" },
            new Person { FirstName = "Carl", LastName = "Marks" },
        };

        listView.ItemTemplate = new DataTemplate(typeof(TextCell));
        listView.ItemTemplate.SetBinding(TextCell.TextProperty, "FirstName");
        listView.ItemSelected += async (sender, e) => {
            await DisplayAlert ("Tapped!", e.SelectedItem + " was tapped.", "OK", "");
        };

        Content = new ContentPage { 
            Content = new StackLayout
            {
                Padding = new Thickness (5,20,5,5),
                Spacing = 10,
                Children = { listView }
            }

        };
    }

}
}

Answer 2

或尝试使用：

await App.Current.MainPage.DisplayAlert("Alert", "your message", "OK");

Answer 3

DisplayAlert()是Page类的方法。

为了让您的类能够使用它，它需要实例化Page对象并使用该对象调用它或直接从它继承。

由于您声明您的Person课程实际上也是Page课程，因此您也可以使用Person个i.e. personObj.DisplayAlert(...)个对象

来调用它

也许类似于以下内容：

var personObj = new Person();
personObj.DisplayAlert ("Tapped!", e.SelectedItem + " was tapped.", "OK", "");

当然，这假设您的Person类声明类似于以下内容：

public class Person : Page
{
    ...
}

显然，具体实现将取决于您如何构建代码。我只是按照你在问题中看到的内容并假设一些事情。

Xamarin表单“... DisplayAlert在当前上下文中不存在。”

3 个答案: