无法检索可观察集合的元素的更新属性

Question

我正在研究 VS2015 上的 UWP 选举指挥。我已经制作了候选 class 并设置其属性如下：

public class Candidate
{
    public int VoteCount { get; set; }
    public string Name { get; set; }
    public string Category { get; set; }
    public CandidateSNo S_no { get; set; }
    public CandidateCategoryNo Category_no { get; set; }
}

public enum CandidateCategoryNo
{
    I,
    II,
    III,
    IV,
    V,
    VI
}

public enum CandidateSNo
{
    I,
    II,
    III
}

我制作了一个 CandidateManager class 来存储方法，并且在其中，我在一个方法中存储了一个可观察的集合，其中每个候选者都包含 5 个属性。这是 CandidateManager class:

private static ObservableCollection<Candidate> getCandidate()
    {
        var _candidate = new ObservableCollection<Candidate>();

        _candidate.Add(new Candidate() { S_no = CandidateSNo.I, Category_no = CandidateCategoryNo.I, VoteCount = 0, Category = "President", Name = "A" });
        _candidate.Add(new Candidate() { S_no = CandidateSNo.II, Category_no = CandidateCategoryNo.I, VoteCount = 0, Category = "President", Name = "B" });
        _candidate.Add(new Candidate() { S_no = CandidateSNo.III, Category_no = CandidateCategoryNo.I, VoteCount = 0, Category = "President", Name = "C" });

        return _candidate;
    }

public static ObservableCollection<Candidate> GetAllCandidates()
            {
                ObservableCollection<Candidate> Candidates = CandidateManager.getCandidate();
                return Candidates;
            }

我希望每当有人选择他们的名字按钮时，每个候选人的投票数都会增加 1。我在页面上制作了 3 个用于选择候选人的按钮和一个提交按钮以提交他们的选择。之后，结果文本块将显示选择了哪个候选人。这是主页的 XAML：

    <Button Name="Cand2" Width="100" Height="100" FontSize="20" HorizontalAlignment="Center" VerticalAlignment="Top" Click="Cand2_Click"/>

    <Button Name="Cand3" Width="100" Height="100" FontSize="20" HorizontalAlignment="Right" VerticalAlignment="Top" Click="Cand3_Click"/>

    <TextBlock HorizontalAlignment="Center" VerticalAlignment="Center" Width="200" Height="50" FontSize="30" Name="Res"/>

    <Button Name="Submit" VerticalAlignment="Bottom" HorizontalAlignment="Center" Content="Submit" Click="Submit_Click" />

</Grid>

这是 xaml.cs：

public MainPage()
    {
        this.InitializeComponent();
        ObservableCollection<Candidate> Candidates = CandidateManager.GetAllCandidates();

        Cand1.Content = CandidateManager.GetCandidateByCategoryAndSno(CandidateCategoryNo.I, CandidateSNo.I).Name;
        Cand2.Content = CandidateManager.GetCandidateByCategoryAndSno(CandidateCategoryNo.I, CandidateSNo.II).Name;
        Cand3.Content = CandidateManager.GetCandidateByCategoryAndSno(CandidateCategoryNo.I, CandidateSNo.III).Name;
    }

    private void Cand1_Click(object sender, RoutedEventArgs e)
    {
        ObservableCollection<Candidate> Candidates = CandidateManager.GetAllCandidates();
        Candidate chosenOne = Candidates.Where(c => c.Name == Cand1.Content).FirstOrDefault();
        chosenOne.VoteCount += 1;
        Candidates.Where(c => c.Name == Cand1.Content).FirstOrDefault().VoteCount = chosenOne.VoteCount;
    }

    private void Cand2_Click(object sender, RoutedEventArgs e)
    {
        ObservableCollection<Candidate> Candidates = CandidateManager.GetAllCandidates();
        Candidate chosenOne = Candidates.Where(c => c.Name == Cand2.Content).FirstOrDefault();
        chosenOne.VoteCount += 1;
        Candidates.Where(c => c.Name == Cand2.Content).FirstOrDefault().VoteCount = chosenOne.VoteCount;
    }

    private void Cand3_Click(object sender, RoutedEventArgs e)
    {
        ObservableCollection<Candidate> Candidates = CandidateManager.GetAllCandidates();
        Candidate chosenOne = Candidates.Where(c => c.Name == Cand3.Content).FirstOrDefault();
        chosenOne.VoteCount += 1;
        Candidates.Where(c => c.Name == Cand3.Content).FirstOrDefault().VoteCount = chosenOne.VoteCount;
    }

    private void Submit_Click(object sender, RoutedEventArgs e)
    {
        ObservableCollection<Candidate> Candidates = CandidateManager.GetAllCandidates();
        Candidate chosenOne = Candidates.Where(c => c.VoteCount == 1).FirstOrDefault();
        if (chosenOne != null)
            Res.Text = chosenOne.Name + " -- " + chosenOne.VoteCount.ToString();
        else
            Res.Text = "null";
    }

我面临的问题是我无法检索更新的投票计数，结果文本块显示为空。这只是主项目的一个小虚拟，但我在主程序中面临同样的问题。我想在程序运行时更新候选人的投票数和其他属性，并在需要时检索它们。为长代码道歉。希望你能帮忙..谢谢！

Answer 1

您应该使用 class 级变量进行可观察集合并对其进行更改。

您的代码存在问题，每个方法都有自己的本地可观察集合实例。我编辑了你的代码隐藏部分，请参阅

   ObservableCollection<Candidate> Candidates = null;
    public MainPage()
    {
        this.InitializeComponent();
        Candidates = CandidateManager.GetAllCandidates();

        Cand1.Content = CandidateManager.GetCandidateByCategoryAndSno(CandidateCategoryNo.I, CandidateSNo.I).Name;
        Cand2.Content = CandidateManager.GetCandidateByCategoryAndSno(CandidateCategoryNo.I, CandidateSNo.II).Name;
        Cand3.Content = CandidateManager.GetCandidateByCategoryAndSno(CandidateCategoryNo.I, CandidateSNo.III).Name;
    }

    private void Cand1_Click(object sender, RoutedEventArgs e)
    {
        Candidate chosenOne = Candidates.Where(c => c.Name == Cand1.Content).FirstOrDefault();
        chosenOne.VoteCount += 1;
        Candidates.Where(c => c.Name == Cand1.Content).FirstOrDefault().VoteCount = chosenOne.VoteCount;
    }

    private void Cand2_Click(object sender, RoutedEventArgs e)
    {
        Candidate chosenOne = Candidates.Where(c => c.Name == Cand2.Content).FirstOrDefault();
        chosenOne.VoteCount += 1;
        Candidates.Where(c => c.Name == Cand2.Content).FirstOrDefault().VoteCount = chosenOne.VoteCount;
    }

    private void Cand3_Click(object sender, RoutedEventArgs e)
    {
        Candidate chosenOne = Candidates.Where(c => c.Name == Cand3.Content).FirstOrDefault();
        chosenOne.VoteCount += 1;
        Candidates.Where(c => c.Name == Cand3.Content).FirstOrDefault().VoteCount = chosenOne.VoteCount;
    }

    private void Submit_Click(object sender, RoutedEventArgs e)
    {
        Candidate chosenOne = Candidates.Where(c => c.VoteCount == 1).FirstOrDefault();
        if (chosenOne != null)
            Res.Text = chosenOne.Name + " -- " + chosenOne.VoteCount.ToString();
        else
            Res.Text = "null";
    }

无法检索可观察集合的元素的更新属性

Unable to retrieve an updated property of an element of an observable collection

c#

xaml

class

observablecollection

uwp

无法检索可观察集合的元素的更新 属性

Unable to retrieve an updated property of an element of an observable collection

c#

xaml

class

observablecollection

uwp

无法检索可观察集合的元素的更新属性