如何在xamarin表单中使用单例类来获取和发布json值？

public class JsonManager
{
    private static JsonManager instance;
    private string jsonValue;

    private JsonManager()
    {
        // 私有构造函数，防止外部实例化
    }

    public static JsonManager Instance
    {
        get
        {
            if (instance == null)
            {
                instance = new JsonManager();
            }
            return instance;
        }
    }

    public string GetJsonValue()
    {
        return jsonValue;
    }

    public void SetJsonValue(string value)
    {
        jsonValue = value;
    }
}

public class MainPage : ContentPage
{
    private Label jsonLabel;

    public MainPage()
    {
        jsonLabel = new Label();

        // 获取JSON值
        string jsonValue = JsonManager.Instance.GetJsonValue();

        // 在标签控件上显示JSON值
        jsonLabel.Text = jsonValue;

        Content = new StackLayout
        {
            Children = { jsonLabel }
        };
    }
}

public class FormPage : ContentPage
{
    private Entry jsonEntry;
    private Button saveButton;

    public FormPage()
    {
        jsonEntry = new Entry();
        saveButton = new Button { Text = "Save" };
        saveButton.Clicked += SaveButton_Clicked;

        Content = new StackLayout
        {
            Children = { jsonEntry, saveButton }
        };
    }

    private void SaveButton_Clicked(object sender, EventArgs e)
    {
        // 获取用户输入的JSON值
        string jsonValue = jsonEntry.Text;

        // 设置JSON值到单例类中
        JsonManager.Instance.SetJsonValue(jsonValue);

        // 导航回上一个页面或执行其他操作
    }
}