c# - 在按钮上向父项添加子项单击 Xamarin.forms

Question

我一直在尝试在 Android 中单击按钮时向 Stacklayout 添加标签 View 。 但它抛出空指针异常。以下是我想要实现的目标。谁能就如何在 xamarin.forms 中实现这一点提出建议

C# 中的 Xamarin.Forms 代码

 StackLayout parent= new StackLayout ();

 Button add= new Button
        {
            HorizontalOptions=LayoutOptions.End,
            BackgroundColor=Xamarin.Forms.Color.White,
            Text="ADD",
            TextColor=Xamarin.Forms.Color.Maroon,
        };

 add.Clicked += OnButtonClicked;
 
 Label firstLabel = new Label
        {
            Text = "Label 1",
            HorizontalOptions = LayoutOptions.StartAndExpand,
            TextColor=Xamarin.Forms.Color.FromHex("#000000")
        };
 parent.Children.Add(add);
 parent.Children.Add(firstLabel );

在 ButtonClick 中添加标签

 void OnButtonClicked(object sender, EventArgs e)
 {

   Label secondLabel = new Label
        {
            Text = "Label 1",
            HorizontalOptions = LayoutOptions.StartAndExpand,
            TextColor=Xamarin.Forms.Color.FromHex("#000000")
        };
  parent.Children.Add(secondLabel ); 
}

提前致谢

Answer 1

您的代码按原样工作...只需一点小改动 - 将 parent 设为类字段，以便从 OnButtonClicked

中引用它

确保更新解决方案包，以便拥有最新的 Xamarin.Forms。始终在解决方案级别更新包，以免发生版本冲突

此版本已经过测试并可在 iOS 上运行:

public class LabelPage: ContentPage
    {
        StackLayout parent = null;

        public LabelPage ()
        {
            parent = new StackLayout ();

            Button add = new Button {
                HorizontalOptions = LayoutOptions.End,
                BackgroundColor = Xamarin.Forms.Color.White,
                Text = "ADD",
                TextColor = Xamarin.Forms.Color.Maroon,
            };

            add.Clicked += OnButtonClicked;

            Label firstLabel = new Label {
                Text = "Label 1",
                HorizontalOptions = LayoutOptions.StartAndExpand,
                TextColor = Xamarin.Forms.Color.FromHex ("#000000")
            };
            parent.Children.Add (add);
            parent.Children.Add (firstLabel); 

            Content = parent;
        }

        void OnButtonClicked (object sender, EventArgs e)
        { 
            Label secondLabel = new Label {
                Text = "Label 1",
                HorizontalOptions = LayoutOptions.StartAndExpand,
                TextColor = Xamarin.Forms.Color.FromHex ("#000000")
            };
            parent.Children.Add (secondLabel); 
            //UpdateChildrenLayout ();
        }
    }