如何设置 XAML ListView 并创建按钮来更新值

Question

首先，如果这个问题没有完全理解，我深表歉意 - 对于 C# 和 XAML。

我是一个完全的新手

我创建了这个 class 人：

class Student
{
    private string studentID;
    public string StudentID
    {
        get { return studentID; }
        set
        {
            studentID = value;
            NotifyPropertyChanged("StudentID");
        }
    }

    private string firstName;
    public string FirstName {
        get { return firstName; }
        set
        {
            firstName = value;
            NotifyPropertyChanged("FirstName");
        }
    }

    private string surname;
    public string Surname
    {
        get { return surname; }
        set
        {
            surname = value;
            NotifyPropertyChanged("Surname");
        }
    }

    private string group;
    public string Group
    {
        get { return group; }
        set
        {
            group = value;
            NotifyPropertyChanged("Group");
        }
    }

    private int cValue;
    public int CValue
    {
        get { return cValue; }
        set
        {
            cValue = value;
            NotifyPropertyChanged("CValue");
        }
    }

    private string teacher;
    public string Teacher
    {
        get { return teacher; }
        set
        {
            teacher = value;
            NotifyPropertyChanged("Teacher");
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    private void NotifyPropertyChanged([CallerMemberName] string caller = "")
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(caller));
        }
    }

    public Student() { }

    public Student(string studentID, string firstName, string surname, string group, int cValue, string teacher)
    {
        StudentID = studentID;
        FirstName = firstName;
        Surname = surname;
        Group = group;
        CValue = cValue;
        Teacher = teacher;
    }


    // strings used to create random students
    private static readonly string[] firstNames = { "Adam", "Bob", "Carl", "David", "Edgar", "Frank", "George", "Harry", "Isaac", "Jesse", "Ken", "Larry" };
    private static readonly string[] surnames = { "Adamson", "Bobson", "Carlson", "Davidson", "Edgarson", "Frankson", "Georgeson", "Harryson", "Isaacson", "Jesseson", "Kenson", "Larryson" };
    private static readonly string[] groups = { "6a", "5b" };
    private static readonly string[] teachers = { "Fred", "Jim"};

    // method to create random students
    public static IEnumerable<Student> CreateStudents(int count)
    {
        var people = new List<Student>();

        var r = new Random();

        for (int i=0; i< count; i++)
        {
            StringBuilder builder = new StringBuilder();
            builder.Append("A");
            builder.Append(i.ToString());
            string num = builder.ToString();
            var s = new Student()
            {
                StudentID = num,
                FirstName = firstNames[r.Next(firstNames.Length)],
                Surname = surnames[r.Next(surnames.Length)],
                Group = groups[r.Next(groups.Length)],
                Teacher = teachers[r.Next(teachers.Length)]
            };
            people.Add(s);
        }
        return people;
    }

}

然后我创建了这些人物对象的列表，我可以很容易地将这个列表绑定到 list/grid 视图。

不过我想做的是在每个项目上有一个加号和减号按钮以从那个人的 CValue 中添加或减去 1。（我会上传图片来演示，但不会让我...）

我如何布置 XAML 并为此添加绑定，即使像我这样的白痴也能理解？

谢谢！

Answer 1

如你所见here，PropertyChanged事件是INotifyPropertyChanged的接口事件，所以我认为你的class'Student'需要显式实现这个接口。

public class Student : INotifyPropertyChanged

也许 this 实施指南可以帮助您。

Answer 2

您需要使用 Observable Collection 而不是 List

然后您所要做的就是根据需要操作此列表，它会自动将更改通知 UI

Answer 3

您需要在您的学生 VM 上使用 RelayCommand 或 DelegateCommand。它们不是 WPF 的一部分，但都是 ICommand 的常用实现，可直接在您的 VM 中调用委托，并在 MVVM 中广泛使用。然后，您可以将按钮 Command 直接绑定到它们：

class Student : INotifyPropertyChanged
{
    ICommand AddCommand    { get; private set; }
    ICommand RemoveCommand { get; private set; }

    public Student()
    {
        this.AddCommand = new RelayCommand(Add);
        this.RemoveCommand = new RelayCommand(Remove);
    }

    private Add()
    {
        this.CValue++;
    }

    private Remove()
    {
        this.CValue--;
    }

    //snip rest of Student properties
}

在您的 XAML 学生模板中：

<Button Command="{Binding AddCommand>" Content="Add"/>
<Button Command="{Binding RemoveCommand>" Content="Remove"/>

如果您希望让 Student 对象不受 VM 东西的影响（即它纯粹是一个模型 class），那么您可以在父 VM 上实现相同的命令，但将学生对象作为命令传递参数：

class StudentsVM: INotifyPropertyChanged
{
    ICommand AddCommand    { get; private set; }
    ICommand RemoveCommand { get; private set; }

    public StudentsVM()
    {
        this.AddCommand = new RelayCommand<Student>(Add);
        this.RemoveCommand = new RelayCommand<Student>(Remove);
    }

    private Add(Student student)
    {
        student.CValue++;
    }

    private Remove(Student student)
    {
        student.CValue--;
    }

    //snip rest of Student properties
}

在您的 XAML 学生模板中：

<Button Command="{Binding DataContext.AddCommand, ElementName=root}"
        CommandParameter="{Binding}"
        Content="Add"/>
<Button Command="{Binding DataContext.RemoveCommand, ElementName=root}" 
        CommandParameter="{Binding}"
        Content="Remove"/>

其中 "root" 是您的父视图。这只是在父视图中获取命令的一种方式，如果您愿意，可以改用 RelativeSource。

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