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xamarin - 有没有办法让标签从左到右填充空间？

转载 作者：行者123 更新时间：2023-12-03 14:46:20 27 4
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这是我的代码:

<StackLayout>
   <Label x:Name="emptyLabel1" FontSize="18" XAlign="Start" TextColor="Gray" />
   <Label x:Name="emptyLabel2" FontSize="18" XAlign="Center" TextColor="Gray" />
   <Label x:Name="emptyLabel3" FontSize="18" XAlign="Center" TextColor="Gray" />
</StackLayout>

第一个多行标签从左侧开始，但在右侧的某些行上有空格。第二个和第三个多行标签居中，左右两边都有空格。

有什么方法可以让标签的所有行完全填充行从左到右完全填充 o 每行的第一个字符总是排在左边，每行最后一个单词的最后一个字符总是排成一行在右边？请注意，这需要每行中的一些单词在它们之间具有不同的间隙。

最佳答案

实现带有对齐对齐支持的标签有点棘手，但可以通过平台渲染器实现。

第一步是在表单项目中声明一个自定义控件。

public class JustifiedLabel : Label { }

下一步是在 iOS 中定义和注册平台渲染器。这个很简单，因为我们只需将格式化字符串与段落样式结合起来就可以得到我们想要的。 
[assembly: ExportRenderer(typeof(JustifiedLabel), typeof(JustifiedLabelRenderer))]
namespace SomeAppNamespace.iOS
{   
    public class JustifiedLabelRenderer : LabelRenderer
    {
        protected override void OnElementChanged(ElementChangedEventArgs<Label> e)
        {
            base.OnElementChanged(e);

            //if we have a new forms element, we want to update text with font style (as specified in forms-pcl) on native control
            if (e.NewElement != null)
                UpdateTextOnControl();
        }

        protected override void OnElementPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
        {
            base.OnElementPropertyChanged(sender, e);

            //if there is change in text or font-style, trigger update to redraw control
            if(e.PropertyName == nameof(Label.Text) 
               || e.PropertyName == nameof(Label.FontFamily) 
               || e.PropertyName == nameof(Label.FontSize)
               || e.PropertyName == nameof(Label.TextColor)
               || e.PropertyName == nameof(Label.FontAttributes))
            {
                UpdateTextOnControl();
            }
        }

        void UpdateTextOnControl()
        {
            if (Control == null)
                return;

            //define paragraph-style
            var style = new NSMutableParagraphStyle()
            {
                Alignment = UITextAlignment.Justified,
                FirstLineHeadIndent = 0.001f,
            };

            //define attributes that use both paragraph-style, and font-style 
            var uiAttr = new UIStringAttributes()
            {
                ParagraphStyle = style,
                BaselineOffset = 0,

                Font = Control.Font
            };

            //define frame to ensure justify alignment is applied
            Control.Frame = new RectangleF(0, 0, (float)Element.Width, (float)Element.Height);

            //set new text with ui-style-attributes to native control (UILabel)
            var stringToJustify = Control.Text ?? string.Empty;
            var attributedString = new Foundation.NSAttributedString(stringToJustify, uiAttr.Dictionary);
            Control.AttributedText = attributedString;
            Control.Lines = 0;
        }
    }
}

在 android 平台上，它有点棘手 - 因为 android 不支持为 TextView 对齐对齐。 - 所以我们需要使用 WebView而是让它渲染文本。

( 注意: 你也可以 alternatively use an android library 并用它代替 WebView ) 
[assembly: ExportRenderer(typeof(JustifiedLabel), typeof(JustifiedLabelRenderer))]
namespace SomeAppNamespace.Droid
{
    //We don't extend from LabelRenderer on purpose as we want to set 
    // our own native control (which is not TextView)
    public class JustifiedLabelRenderer : ViewRenderer
    {
        protected override void OnElementChanged(ElementChangedEventArgs<View> e)
        {
            base.OnElementChanged(e);

            //if we have a new forms element, we want to update text with font style (as specified in forms-pcl) on native control
            if (e.NewElement != null)
            {
                if (Control == null)
                {
                    //register webview as native control
                    var webView = new Android.Webkit.WebView(Context);
                    webView.VerticalScrollBarEnabled = false;
                    webView.HorizontalScrollBarEnabled = false;

                    webView.LoadData("<html><body>&nbsp;</body></html>", "text/html; charset=utf-8", "utf-8");
                    SetNativeControl(webView);
                }

                //if we have a new forms element, we want to update text with font style (as specified in forms-pcl) on native control
                UpdateTextOnControl();
            }   
        }

        protected override void OnElementPropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
        {
            base.OnElementPropertyChanged(sender, e);

            //if there is change in text or font-style, trigger update to redraw control
            if (e.PropertyName == nameof(Label.Text)
               || e.PropertyName == nameof(Label.FontFamily)
               || e.PropertyName == nameof(Label.FontSize)
               || e.PropertyName == nameof(Label.TextColor)
               || e.PropertyName == nameof(Label.FontAttributes))
            {
                UpdateTextOnControl();
            }
        }

        void UpdateTextOnControl()
        {
            var webView = Control as Android.Webkit.WebView; 
            var formsLabel = Element as Label;

            // create css style from font-style as specified
            var cssStyle = $"margin: 0px; padding: 0px; text-align: justify; color: {ToHexColor(formsLabel.TextColor)}; background-color: {ToHexColor(formsLabel.BackgroundColor)}; font-family: {formsLabel.FontFamily}; font-size: {formsLabel.FontSize}; font-weight: {formsLabel.FontAttributes}";

            // apply that to text 
            var strData =
                $"<html><body style=\"{cssStyle}\">{formsLabel?.Text}</body></html>";

            // and, refresh webview
            webView.LoadData(strData, "text/html; charset=utf-8", "utf-8");
            webView.Reload();
        }

        // helper method to convert forms-color to css-color
        string ToHexColor(Color color)
        {
            var red = (int)(color.R * 255);
            var green = (int)(color.G * 255);
            var blue = (int)(color.B * 255);
            var alpha = (int)(color.A * 255);
            var hex = $"#{red:X2}{green:X2}{blue:X2}";

            return hex;
        }
    }
}

示例用法 
<StackLayout Margin="20">
    <Entry x:Name="InputEntry" />

    <Label Margin="0,10,0,0" BackgroundColor="Navy" TextColor="White" Text="Normal Text Label" FontSize="15" HorizontalOptions="CenterAndExpand" />
    <Label 
            FontSize="20" 
            FontAttributes="Bold"  
            Text="{Binding Text, Source={x:Reference InputEntry}}" />

    <Label Margin="0,10,0,0" BackgroundColor="Navy" TextColor="White" Text="Justified Text Label" FontSize="15" HorizontalOptions="CenterAndExpand" />
    <local:JustifiedLabel 
            FontSize="20" 
            FontAttributes="Bold" 
            Text="{Binding Text, Source={x:Reference InputEntry}}"
            TextColor="Green"
            BackgroundColor="Yellow"
            VerticalOptions="FillAndExpand"
            HorizontalOptions="FillAndExpand" />

</StackLayout>

enter image description here enter image description here

关于xamarin - 有没有办法让标签从左到右填充空间？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/45995793/

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