Question

所以我有一个横向滚动视图，当用户采取某个动作时，我试图动态填充。我投入到视图中的项目都包含4个使用自定义字体的标签。当我尝试添加大约10个这样的项目时，它在Android上滞后约1.5秒，在IOS上滞后1秒。如果我取出自定义字体，那么在每个平台上大约1秒钟。如果我取出3个标签并且只显示一个，那么它几乎是瞬间完成的。是否有任何已知的滞后原因？是否有任何解决方法，所以我仍然可以使用自定义字体而没有大的延迟？

这是我做的一个快速示例，它几乎完成了我在我的应用中所做的事情。但是，我的应用程序有更多的东西，所以这里的延迟并不是很糟糕，但它仍然非常明显

public class App : Application
{
    public int count;
    public ScrollView scroll, scroll2, scroll3;
    public App ()
    {
        count = 1;
        scroll = new ScrollView {
            VerticalOptions = LayoutOptions.Center,
            Orientation = ScrollOrientation.Horizontal
        };
        scroll2 = new ScrollView {
            VerticalOptions = LayoutOptions.Center,
            Orientation = ScrollOrientation.Horizontal
        };
        Button button = new Button(){
            Text = "click",
        };
        button.Clicked += (sender, e) => AddStuff();
        Button button2 = new Button(){
            Text = "click",
        };
        button2.Clicked += (sender, e) => AddStuff2();
        MainPage = new ContentPage {
            BackgroundColor = Color.White,
            Content = new StackLayout{
                Children={
                    button,
                    scroll,
                    button2,
                    scroll2
                }
            }
        };
    }
    //this one is instantaneous
    public void AddStuff()
    {
        StackLayout stack = new StackLayout () {
            Orientation = StackOrientation.Horizontal,
            HorizontalOptions = LayoutOptions.FillAndExpand,
            HeightRequest = 200,
        };
        for (int i = 0; i < 11; i++)
            stack.Children.Add (
                new StackLayout(){
                    Children = {
                        new Label (){TextColor = Color.Blue, Text = "Size: ", WidthRequest = 100 },
                    }
                }
            );
        scroll.Content = stack;
        count++;
    }
    //this one takes forever
    public void AddStuff2()
    {
        StackLayout stack = new StackLayout () {
            Orientation = StackOrientation.Horizontal,
            HorizontalOptions = LayoutOptions.FillAndExpand,
            HeightRequest = 200,
        };
        for (int i = 0; i < 11; i++)
            stack.Children.Add (
                new StackLayout(){
                    Children = {
                        new Label (){TextColor = Color.Blue, Text = "Size: ", WidthRequest = 100 },
                        new Label (){TextColor = Color.Blue, Text ="" + count*i, WidthRequest = 100 },
                        new Label (){TextColor = Color.Blue, Text = "Size: ", WidthRequest = 100 },
                        new Label (){TextColor = Color.Blue, Text ="" + count*i, WidthRequest = 100 }
                    }
                }
            );
        scroll2.Content = stack;
        count++;
    }
}

和droid的自定义字体标签

[assembly: ExportRenderer (typeof (Label), typeof (CustomFontLabel_Droid))]
    namespace df.Droid
    {
        public class CustomFontLabel_Droid:LabelRenderer
        {
            protected override void OnElementChanged (ElementChangedEventArgs<Xamarin.Forms.Label> e) {
                base.OnElementChanged (e);
                var label = (TextView)Control;
                Typeface font = Typeface.CreateFromAsset (Forms.Context.Assets, "SourceSansPro-Semibold.otf");
                label.Typeface = font;
            }
        }
    }

Answer 1

只是让其他人遇到类似的问题，如果你在Android MainActivity中创建一个静态字体属性而不是每次调用Label.OnElementChanged函数中的createFromAsset那么它就会消除android上的额外延迟。

CustomFontLabel_Droid.cs

[assembly: ExportRenderer (typeof (Label), typeof (CustomFontLabel_Droid))]
namespace df.Droid
{
    public class CustomFontLabel_Droid:LabelRenderer
    {
        protected override void OnElementChanged (ElementChangedEventArgs<Xamarin.Forms.Label> e) {
            base.OnElementChanged (e);
            var label = (TextView)Control;
            // this guy slows things down-> Typeface font = Typeface.CreateFromAsset (Forms.Context.Assets, "SourceSansPro-Semibold.otf");
            label.Typeface = MainActivity.semiBoldFont;
        }
    }
}

MainActivity.cs

public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsApplicationActivity
    {
        public static Typeface semiBoldFont = null;
        protected override void OnCreate (Bundle bundle)
        {
            base.OnCreate (bundle);
            global::Xamarin.Forms.Forms.Init (this, bundle);
            LoadApplication (new App ());
            semiBoldFont = Typeface.CreateFromAsset (Forms.Context.Assets, "SourceSansPro-Semibold.otf");
        }
    }

xamarin表单动态添加自定义字体标签到scrollview非常慢

1 个答案: