运行应用程序后运行命令
问题描述:
我注意到它不仅发生在一个项目中,而且发生在多个发生器上,所以我将提供一个简单示例。我有这样的XAML:运行应用程序后运行命令
<Page
x:Class="TestApp.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:TestApp"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<Grid>
<Button Content="Button" Command="{Binding PressedButton}" HorizontalAlignment="Left" Margin="0,-10,0,-9" VerticalAlignment="Top" Height="659" Width="400"/>
</Grid>
</Page>
我的类绑定数据:
public abstract class ObservableObject : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
if (this.PropertyChanged != null)
{
var e = new PropertyChangedEventArgs(propertyName);
this.PropertyChanged(this, e);
}
}
}
public class Command : ICommand
{
private Action<object> action;
public Command(Action<object> action)
{
this.action = action;
}
public bool CanExecute(object parameter)
{
if (action != null)
{
return true;
}
else
{
return false;
}
}
public event EventHandler CanExecuteChanged;
public void Execute(object parameter)
{
if (action != null)
{
action((string)parameter);
}
}
}
public class TestViewModel : ObservableObject
{
public ICommand PressedButton
{
get
{
return new Command((param) => { });
}
}
}
和主页:
public MainPage()
{
this.InitializeComponent();
this.NavigationCacheMode = NavigationCacheMode.Required;
DataContext = new TestViewModel();
}
这很奇怪,但PressedButton只有在应用程序启动运行(ISN”它奇怪,它开始运行?)。之后,即使点击按钮后也没有任何事件触发。我无法弄清楚什么是错的。
答
我想你可能会通过每次调用“getter”时返回一个新命令而导致绑定问题。尝试在构造函数中设置一次命令(例如)。
public MainPage()
{
PressedAdd = new Command(param => SaveNote());
}
public ICommand PressedAdd { get; private set; }
在SaveNote()
方法,你可以测试值,然后保存(或不保存)其中:
private void SaveNote()
{
if (NoteTitle == null || NoteContent == null)
return;
// Do something with NoteTitle and NoteContent
}