Question

我在绝对布局中设计了一个活动指示器。基于按钮单击事件，我尝试交替显示和隐藏活动指示器。但由于某种原因，我看不到我的活动指标。任何帮助将不胜感激!!!提前谢谢。

这是我的.xaml.cs类：

public partial class PBTestPage : ContentPage
{
    private bool _pbIndicator;
    public PBTestPage()
    {
        InitializeComponent();
    }

    public bool PBIndicator{
        get{
            return _pbIndicator;
        }set{
            _pbIndicator = value;
            OnPropertyChanged();
        }
    }

    protected override void OnAppearing()
    {
        base.OnAppearing();
        var parentLayout = new AbsoluteLayout();

        var stackContent = new StackLayout();
        AbsoluteLayout.SetLayoutFlags(stackContent,AbsoluteLayoutFlags.PositionProportional);
        AbsoluteLayout.SetLayoutBounds(stackContent,new Rectangle(0f,0f,AbsoluteLayout.AutoSize,AbsoluteLayout.AutoSize));

        var activityIndicator = new ActivityIndicator
        {
            Color = Color.Black,
            IsRunning = PBIndicator,
            IsVisible = PBIndicator
        };
        AbsoluteLayout.SetLayoutFlags(activityIndicator, AbsoluteLayoutFlags.PositionProportional);
        AbsoluteLayout.SetLayoutBounds(activityIndicator, new Rectangle(.5, .5, AbsoluteLayout.AutoSize, AbsoluteLayout.AutoSize));

        var button = new Button
        {
            Text="Click",
            VerticalOptions=LayoutOptions.CenterAndExpand,
            HorizontalOptions=LayoutOptions.CenterAndExpand,
        };
        button.Clicked += OnClicked;

        stackContent.Children.Add(button);

        parentLayout.Children.Add(stackContent);
        parentLayout.Children.Add(activityIndicator);

        Content = parentLayout;
    }

    private void OnClicked(object sender, EventArgs e)
    {
        if(PBIndicator==false){
            PBIndicator = true;
        }else{
            PBIndicator = false;
        }

    }
}

Answer 1

我推断您打算使用OnPropertyChanged来使用绑定，所以现在是开始这样做的好时机。

我已经对您的代码进行了一些更改，我猜它现在可以正常运行了。变化是：

将布局创建移动到构造函数（我无法在每次页面显示时创建相同的布局作为一个好选择）;
OnClicked事件只是反转属性的值，不需要在使用if之前检查它;
使用Bindings处理ActivityIndicator的属性状态;
在true事件中将PBIndicator设置为OnAppearing属性。

这是更改的代码：

public partial class PBTestPage : ContentPage
{
    private bool _pbIndicator;
    public bool PBIndicator
    {
        get { return _pbIndicator; }
        set
        {
            _pbIndicator = value;
            OnPropertyChanged();
        }
    }

    public PBTestPage()
    {
        InitializeComponent();

        var parentLayout = new AbsoluteLayout();

        var stackContent = new StackLayout();
        AbsoluteLayout.SetLayoutFlags(stackContent, AbsoluteLayoutFlags.PositionProportional);
        AbsoluteLayout.SetLayoutBounds(stackContent, new Rectangle(0f, 0f, AbsoluteLayout.AutoSize, AbsoluteLayout.AutoSize));

        var activityIndicator = new ActivityIndicator
        {
            Color = Color.Black
        };

        activityIndicator.SetBinding(ActivityIndicator.IsRunningProperty, new Binding(nameof(PBIndicator)));
        activityIndicator.SetBinding(ActivityIndicator.IsVisibleProperty, new Binding(nameof(PBIndicator)));
        activityIndicator.BindingContext = this;

        AbsoluteLayout.SetLayoutFlags(activityIndicator, AbsoluteLayoutFlags.PositionProportional);
        AbsoluteLayout.SetLayoutBounds(activityIndicator, new Rectangle(.5, .5, AbsoluteLayout.AutoSize, AbsoluteLayout.AutoSize));

        var button = new Button
        {
            Text = "Click",
            VerticalOptions = LayoutOptions.CenterAndExpand,
            HorizontalOptions = LayoutOptions.CenterAndExpand,
        };
        button.Clicked += OnClicked;

        stackContent.Children.Add(button);

        parentLayout.Children.Add(stackContent);
        parentLayout.Children.Add(activityIndicator);

        Content = parentLayout;
    }

    protected override void OnAppearing()
    {
        base.OnAppearing();
        PBIndicator = true;
    }

    private void OnClicked(object sender, EventArgs e)
    {
        PBIndicator = !PBIndicator;
    }
}

让我知道它是否有效。我希望它有所帮助。

Answer 2

试试这个

{{1}}

活动指标在Xamarin.Forms中不起作用

2 个答案: