Xamarin Forms-更新標簽值

Question

昨晚，我花了5個小時試圖弄清楚如何在Xamarin Forms中更新標簽值，但卻一無所獲。

我的xaml看起來像這樣：

<?xml version="1.0" encoding="UTF-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" x:Class="Meditation.HomePage">
<ContentPage.Content>
    <Button Text="{Binding SelectedSound}" HorizontalOptions="Center" VerticalOptions="CenterAndExpand" Clicked="OnButtonClicked" />
</ContentPage.Content>

我的主頁類如下所示：

using System;
using System.Collections.Generic;
using Xamarin.Forms;

namespace Meditation
{
public partial class HomePage : ContentPage
{
    public String SelectedSound { get; set; } 

    public HomePage()
    {
        InitializeComponent();

        this.Title = AppInfo.AppName; 
    }

    protected override void OnAppearing()
    {
        ShowSelectedSound();
        BindingContext = this;
    }

    protected override void OnDisappearing()
    {
        DependencyService.Get<IAudio>().StopAudio();
    }

    // User Actions

    void OnButtonClicked(object sender, EventArgs args)
    {
        Navigation.PushAsync(new SoundSelectionPage());
    }

    // Private

    private void ShowSelectedSound()
    {
        if (Application.Current.Properties.ContainsKey(AppInfo.keySoundSelected))
        {
            SelectedSound = Application.Current.Properties[AppInfo.keySoundSelected] as string;
        }                                      

        else
        {
            this.SelectedSound = "Choose sound";
        }
    }
}
}

首次加載頁面時，該按鈕正確顯示為“選擇聲音”文本。 但是，當返回application.current.properties鍵值時，它無法更新文本。

任何人都知道為什么標簽似乎僅在頁面首次加載而不進行時才更新。 更重要的是，任何人都可以提供代碼來使按鈕文本在初始設置后進行更新嗎？

Answer 1

您必須在homepage類中實現INotifyPropertyChanged才能更新頁面。

public partial class HomePage : ContentPage,  INotifyPropertyChanged
{

        private string selectedSound;
        public string SelectedSound
        {
            get
            {
                return selectedSound;
            } set
            {
                if (selectedSound!=value)
                {
                    selectedSound = value;
                    this.OnPropertyChanged("SelectedSound");
                }
            }
        }

   .....

public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName){
        if (PropertyChanged != null {
            PropertyChanged(this,
                new PropertyChangedEventArgs(propertyName));}}

}

但我建議實現MVVM pattern並定義一個ViewModel 。