Xamarin Forms，快速按下按钮打开 2x 相同的窗口答案

【问题标题】：Xamarin Forms, quickly pressing the button opens 2x the same windowXamarin Forms，快速按下按钮打开 2x 相同的窗口
【发布时间】：2017-11-22 10:59:43
【问题描述】：

当我单击重定向到新窗口的图标时，它会打开相同的视图两次。而且我不知道如何处理它只打开一个视图。

示例 xaml 按钮

<local:AnimatedImage Grid.Column="2" Source="googlemap_view_search.png"
                    HorizontalOptions="Center" VerticalOptions="Center" Margin="16,0">
                <Image.GestureRecognizers>
                    <TapGestureRecognizer Command="{Binding SearchCommand}" />
                </Image.GestureRecognizers>
            </local:AnimatedImage>

自定义动画图像类

 public class AnimatedImage : Image
{
    private const int ANIMATED_TIME = 100;
    private const double INITIAL_VALUE = 1;
    private const double MAGNIFICATION_VALUE = 1.3;

    public static readonly BindableProperty CommandProperty = BindableProperty.Create<AnimatedImage, ICommand>(p => p.Command, null);
    public ICommand Command
    {
        get { return (ICommand)GetValue(CommandProperty); }
        set { SetValue(CommandProperty, value); }
    }

    public static readonly BindableProperty CommandParameterProperty = BindableProperty.Create<AnimatedImage, object>(p => p.CommandParameter, null);
    public object CommandParameter
    {
        get { return (object)GetValue(CommandParameterProperty); }
        set { SetValue(CommandParameterProperty, value); }
    }

    private ICommand TransitionCommand
    {
        get
        {
            return new Command(async () =>
            {
                this.AnchorX = 0.48;
                this.AnchorY = 0.48;
                await this.ScaleTo(MAGNIFICATION_VALUE, 50, Easing.Linear);
                await Task.Delay(ANIMATED_TIME);
                await this.ScaleTo(INITIAL_VALUE, 50, Easing.Linear);
                if (Command != null)
                {
                    Command.Execute(CommandParameter);
                }
            });
        }
    }

    public AnimatedImage()
    {
        Initialize();
    }

    public void Initialize()
    {
        GestureRecognizers.Add(new TapGestureRecognizer()
        {
            Command = TransitionCommand
        });
    }
}

}

在 ViewModel 中 public DelegateCommand SearchCommand { get;私人套装； } 和

    await NavigateToPage(new SearchPage());

【问题讨论】：

每次调用getter都返回new Command？

标签： c# xamarin.forms

【解决方案1】：

问题在于，当您在执行搜索命令之前await 动画时，没有什么可以阻止用户再次启动该命令。您可以在输入命令时添加一个设置为true 的布尔变量，如果该命令已在执行，则忽略第二个用户点击。

private ICommand TransitionCommand
{
    get
    {
        bool isExecuting = false;
        return new Command(async () =>
        {
            if(isExecuting) return;
            isExecuting = true
            try
            {
                this.AnchorX = 0.48;
                this.AnchorY = 0.48;
                await this.ScaleTo(MAGNIFICATION_VALUE, 50, Easing.Linear);
                await Task.Delay(ANIMATED_TIME);
                await this.ScaleTo(INITIAL_VALUE, 50, Easing.Linear);
                if (Command != null)
                {
                    Command.Execute(CommandParameter);
                }
             }
             finally 
             {
                  isExecuting = false;
             }
        });
    }
}

【讨论】：

【解决方案2】：

Xamarin Command 具有 CanExecute 方法，可用于根据您的业务逻辑阻止执行命令。

public ICommand SearchCommand {get; private set; }

bool _canSearch = true;
public bool CanSearch 
{ 
    get { return _canSearch; } 
    private set { 
        _canSearch = value;
        ((Command)SearchCommand).ChangeCanExecute(); 
    }
}

public SearchPageViewModel()
{
    SearchCommand = new Command(() => DoSearchStuff(), () => CanSearch)
}

void DoSearchStuff()
{
    CanSearch = false;
    // long searching stuff
    CanSearch = true;
}

希望对你有帮助

【讨论】：