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rochitsen's questions

Martin Hope
rochitsen
Asked: 2025-04-30 13:52:06 +0800 CST
  • 6

CommandParameter我在 .net maui 9 中有一个下面的小例子，其中我通过在视图中单击按钮时设置的值来设置视图模型中的属性。

然后将此属性用作视图的属性BindingContext。因此，单击按钮时应显示的文本为。PlaceHolderTextEntryEntrySet PropertyOneText from Property

查看以下代码：

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="MauiBindingExample.MainPage"
             xmlns:local="clr-namespace:MauiBindingExample.ViewModels">

    <ScrollView>
        <VerticalStackLayout 
            Padding="30,0"
            Spacing="25">
            <Image
                Source="dotnet_bot.png"
                HeightRequest="185"
                Aspect="AspectFit"
                SemanticProperties.Description="dot net bot in a hovercraft number nine" />
            <Button
                BindingContext="{local:ExampleViewModel}"
                x:DataType="local:ExampleViewModel"
                Text="Set PropertyOne" 
                Command="{Binding SetPropertyOneCommand}"
                CommandParameter="Text from Property"/>
            <Entry
                BindingContext="{local:ExampleViewModel}"
                x:DataType="local:ExampleViewModel"
                PlaceholderColor="AliceBlue"
                Placeholder="{Binding EntryPlaceholderText}"/>
        </VerticalStackLayout>
    </ScrollView>
</ContentPage>

视图模型的代码如下：

using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Windows.Input;

namespace MauiBindingExample.ViewModels
{
    public class ExampleViewModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        private string entryPlaceholderText;

        public string EntryPlaceholderText
        {
            get => entryPlaceholderText;
            set
            {
                entryPlaceholderText = value;
                OnPropertyChanged();
            }
        }
        
        public ICommand SetPropertyOneCommand { get; set; }

        public ExampleViewModel()
        {
            SetPropertyOneCommand = new Command<string>(
                (string arg) =>
                {
                    EntryPlaceholderText = arg;
                });
        }
        public void OnPropertyChanged([CallerMemberName] string propertyName="")
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

当我设置调试器时，我可以确认单击按钮时属性EntryPlaceholderText设置正确Set PropertyOne，但是在命令执行完成后，属性EntryPlaceholderText被重置，因此没有Entry显示占位符文本。

可能存在什么问题？

非常感谢您的帮助。

maui