如何在页面 C# Xamarin 出现时使 currentindex 成为正确的数字而不是 0

Question

我有一个名为 stepview 的 class，它基于 btnBack（后面 1 个数字）或 btnNext（前面 1 个数字）根据来自 json 的 contentid 更改文本。这有效，但不是在出现时，因为那时我看不到图像，因为那时索引为 0。

currentindex 应该等于我的 json 文件的 contentid，现在只能正确使用我的标签文本，显示已经基于 id 的正确文本。

唯一适用于照片的是，如果您单击下一步或后退，您将看到照片，但用户首先结束的页面并非如此。我该如何解决？

这是我的 btnNext 和 btnBack，用于根据 json

的 contentid 中的索引显示文本 + 图像

 public void BtnBack_Clicked(object sender, EventArgs e)
        {
            BtnNext.IsEnabled = true;
            int currentIndex = getCurrentIndex();

            //if its the first item disable back button
            if (currentIndex.Equals(1))
            {
                BtnBack.IsEnabled = false;
            }
            var content = _protocol.Contents[currentIndex - 1];
            _contentId = content.Contentid;
            lblText.Text = content?.Text;
            string protocolName = _protocol.Name;

            //replace space with underscore to get correct picture name
            protocolName = protocolName.Replace(" ", "_");
            myImage.Source = ($"{protocolName}{content?.Contentid}.jpg");

            //get current navTitle on button click
            setNewNavTitle();
        }

        public void BtnNext_Clicked(object sender, EventArgs e)
        {
            BtnBack.IsEnabled = true;
            int currentIndex = getCurrentIndex();
            var content = _protocol.Contents[currentIndex + 1];

            //do something after second last
            if (currentIndex == _protocol.Contents.Count - 2)
            {
                BtnNext.IsEnabled = false;
            }
            _contentId = content.Contentid;
            lblText.Text = content?.Text;
            string protocolName = _protocol.Name;

            //replace space with underscore to get correct picture name
            protocolName = protocolName.Replace(" ", "_");
            myImage.Source = ($"{protocolName}{content?.Contentid}.jpg");

            //get current navTitle on button click
            setNewNavTitle();
        }

当用户第一次进入该页面时，它不显示关联的照片，只显示他在标签中输入的文字

这是为了在 2 次按钮点击时显示照片

myImage.Source = ($"{protocolName}{content?.Contentid}.jpg");

开始时 contentid 似乎为 0

这是我的Json文件

  "protocols": [
    {
      "id": "1",
      "name": "Pols tellen",
      "contents": [
        {
          "chapterTitle": "Voorzorg",
          "contentid": "1",
          "text": "test1"
        },
        {
          "contentid": "2",
          "text": "test2"
        },
        {
          "chapterTitle": "Handeling",
          "contentid": "3",
          "text": "test3"
        },
        {
          "contentid": "4",
          "test1": "test4"
        },
        {
          "chapterTitle": "Nazorg",
          "contentid": "10",
          "text": "test5"
        },
        {
          "contentid": "11",
          "text": "test6"
        }

      ]
    },
}

这是我的 class 用于根据他的 contentid 接收文本和图像（现在仅适用于标签中的文本）

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class StepView : ContentPage
{
    //get index
    private long _contentId;

    //get step
    private Protocol _protocol;

    //go to selected step
    public StepView(Protocol protocol, string title, string chapterTitle, long contentId)
    {
        _protocol = protocol;
        InitializeComponent();
        Title = title + " - " + chapterTitle;

        // get label text
        lblText.Text = protocol.Contents.FirstOrDefault(x => x.ChapterTitle == chapterTitle).Text;
        _contentId = contentId;
    }

    public void BtnBack_Clicked(object sender, EventArgs e)
    {
        BtnNext.IsEnabled = true;
        int currentIndex = getCurrentIndex();

        //if its the first item disable back button
        if (currentIndex.Equals(1))
        {
            BtnBack.IsEnabled = false;
        }
        var content = _protocol.Contents[currentIndex - 1];
        _contentId = content.Contentid;
        lblText.Text = content?.Text;
        string protocolName = _protocol.Name;

        //replace space with underscore to get correct picture name
        protocolName = protocolName.Replace(" ", "_");
        myImage.Source = ($"{protocolName}{content?.Contentid}.jpg");

        //get current navTitle on button click
        setNewNavTitle();
    }

    //go back to home
    public async void btnHome_Clicked(object sender, EventArgs e)
    {
        //go to mainpage
        await Navigation.PushAsync(new MainPage());
    }

    public void BtnNext_Clicked(object sender, EventArgs e)
    {
        BtnBack.IsEnabled = true;
        int currentIndex = getCurrentIndex();
        var content = _protocol.Contents[currentIndex + 1];

        //do something after second last
        if (currentIndex == _protocol.Contents.Count - 2)
        {
            BtnNext.IsEnabled = false;
        }
        _contentId = content.Contentid;
        lblText.Text = content?.Text;
        string protocolName = _protocol.Name;

        //replace space with underscore to get correct picture name
        protocolName = protocolName.Replace(" ", "_");
        myImage.Source = ($"{protocolName}{content?.Contentid}.jpg");

        //get current navTitle on button click
        setNewNavTitle();
    }

    private string getChapterTitle()
    {
        var currentIndex = getCurrentIndex();
        string chapterTitle = _protocol.Contents[currentIndex].ChapterTitle;

        //get the previous or next chapter based on where you clicked on
        while (currentIndex > 0 && string.IsNullOrWhiteSpace(chapterTitle))
        {
            currentIndex -= 1;
            chapterTitle = _protocol.Contents[currentIndex].ChapterTitle;
        }
        return chapterTitle;
    }

    private int getCurrentIndex()
    {
        var currentContent = _protocol.Contents.FirstOrDefault(x => x.Contentid == _contentId);
        var currentIndex = _protocol.Contents.IndexOf(currentContent);
        return currentIndex;
    }

    //get new protocol + chapter based on btnBack and btnNext
    private void setNewNavTitle()
    {
        string nextTitile = _protocol.Name + " - " + getChapterTitle();
        Title = nextTitile;
    }

如何使我的照片标签文本具有相同的效果？提前致谢

Answer 1

只需将其添加到页面构造函数的末尾

myImage.Source = ($"{protocolName}{content?.Contentid}.jpg");

如何在页面 C# Xamarin 出现时使 currentindex 成为正确的数字而不是 0

How to make currentindex the correct number instead of 0 on appearing of the page C# Xamarin

c#

json

indexof

xamarin