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当我在 CollectionView 中滚动时，它开始滞后，可能正在加载下一张图片。我能用它做什么？我该如何优化它？这是 XAML：当我在 CollectionView 中滚动时，它开始滞后，可能正在加载下一张图片。我能用它做什么？我该如何优化它？这是 XAML： <Grid BackgroundColor="#00aeef"> <Grid.RowDefinitions> <RowDefinition Height="*"/> </Grid.RowDefinitions> <CollectionView x:Name="myCollectionView" Grid.Row="0"> <CollectionView.ItemTemplate> <DataTemplate> <StackLayout> <Frame Padding="0" BackgroundColor="#00d2ff" Margin="20" CornerRadius="30"> <StackLayout Padding="20"> <Label Text="{Binding Airline}" TextColor ="White" FontSize="30" HorizontalOptions="Center"/> <Image Source="{Binding Url}" HeightRequest="200"/> <Label Text="{Binding Plane, StringFormat='Plane: {0}'}" TextColor ="White" FontSize="15"/> <Label Text="{Binding Airline, StringFormat='Airline: {0}'}" TextColor ="White" FontSize="15"/> <Label Text="{Binding Livery, StringFormat='Livery: {0}'}" TextColor ="White" FontSize="15"/> <Label Text="{Binding Registration, StringFormat='Reg: {0}'}" TextColor ="White" FontSize="15"/> <Label Text="{Binding Airport, StringFormat='Airport: {0}'}" TextColor ="White" FontSize="15"/> <Label Text="{Binding Date, StringFormat='Date: {0}'}" TextColor ="White" FontSize="15"/> <Label Text="{Binding Comment, StringFormat='Comment: {0}'}" TextColor ="White" FontSize="15"/> </StackLayout> </Frame> </StackLayout> </DataTemplate> </CollectionView.ItemTemplate> </CollectionView> </Grid> 这是我的代码： public ShowPlanes() { InitializeComponent(); var db = new SQLiteConnection(_dbPath); var data = db.Table<Airplane>().ToList(); myCollectionView.ItemsSource = data; NavigationPage.SetHasNavigationBar(this, false); } 如果您的图像很大，请尝试将其调整为您需要的尺寸，也许会解决这个问题，下面是非常好的参考。 https://learn.microsoft.com/en-us/samples/xamarin/xamarin-forms-samples/xamformsimageresize/ 如果您的图像很大，例如超过 100KB（每个），那么您可以考虑使用不同的文件名和较小的尺寸（例如 10-20KB）为相同图像创建缩略图。这将提高您的应用程序的速度。要调整图像大小，您可以使用以下代码。该功能将保持原始图像的纵横比。此外，代码会将原始图像设置为 72dpi。结果将是一个小的优化文件，准备渲染到您的视图。 using System.Drawing; using System.Drawing.Drawing2D; using System.Drawing.Imaging; ... public static void CreatePreviewImage(string imageFullFilename, string previewFullFilename) { ImageCodecInfo jpgEncoder = GetEncoder(ImageFormat.Jpeg); // Create an Encoder object based on the GUID // for the Quality parameter category. System.Drawing.Imaging.Encoder myEncoder = System.Drawing.Imaging.Encoder.Quality; // Create an EncoderParameters object. // An EncoderParameters object has an array of EncoderParameter // objects. In this case, there is only one // EncoderParameter object in the array. EncoderParameters myEncoderParameters = new EncoderParameters(1); EncoderParameter myEncoderParameter = new EncoderParameter(myEncoder, 75L); //default myEncoderParameters.Param[0] = myEncoderParameter; Bitmap originalimage = (Bitmap)System.Drawing.Image.FromFile(imageFullFilename, true); originalimage.SetResolution(72, 72); int w = originalimage.Width; int h = originalimage.Height; int pw = 0; int ph = 0; h = originalimage.Height * w / originalimage.Width; if (w > h) { pw = 200; ph = h * pw / w; } else { ph = 200; pw = w * ph / h; } Bitmap previewImage = ImageHandlers.ResizeImage(originalimage, pw, ph); previewImage.Save(previewFullFilename, jpgEncoder, myEncoderParameters); } public static Bitmap ResizeImage(Image image, int width, int height) { var h = image.Height; var w = image.Width; if (w > h) { height = h * width / w; } else if( h < w ) { width = w * height / h; } var destRect = new Rectangle(0, 0, width, height); var destImage = new Bitmap(width, height); destImage.SetResolution(image.HorizontalResolution, image.VerticalResolution); using (var graphics = Graphics.FromImage(destImage)) { graphics.CompositingMode = CompositingMode.SourceCopy; graphics.CompositingQuality = CompositingQuality.HighQuality; graphics.InterpolationMode = InterpolationMode.HighQualityBicubic; graphics.SmoothingMode = SmoothingMode.HighQuality; graphics.PixelOffsetMode = PixelOffsetMode.HighQuality; using (var wrapMode = new ImageAttributes()) { wrapMode.SetWrapMode(WrapMode.TileFlipXY); graphics.DrawImage(image, destRect, 0, 0, image.Width, image.Height, GraphicsUnit.Pixel, wrapMode); } } return destImage; } public static ImageCodecInfo GetEncoder(ImageFormat format) { ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders(); foreach (ImageCodecInfo codec in codecs) { if (codec.FormatID == format.Guid) { return codec; } } return null; } 这是调整大小的工作代码： var bitmap = SKBitmap.Decode(Path); int h = bitmap.Height; int w = bitmap.Width; int newWidth = w; int newHeight = h; if (h > 1080 || w > 1080) { int rectHeight = 1080; int rectWidth = 1080; //aspect ratio calculation float W = w; float H = h; float aspect = W / H; await DisplayAlert("aspect", aspect.ToString() + w.ToString() + h.ToString(), "OK"); //new dimensions by aspect ratio newWidth = (int)(rectWidth * aspect); newHeight = (int)(newWidth / aspect); await DisplayAlert("aspect", "h " + newHeight.ToString() + " w " + newWidth.ToString(), "OK"); //if one of the two dimensions exceed the box dimensions if (newWidth > rectWidth || newHeight > rectHeight) { //depending on which of the two exceeds the box dimensions set it as the box dimension and calculate the other one based on the aspect ratio if (newWidth > newHeight) { newWidth = rectWidth; newHeight = (int)(newWidth / aspect); } else { newHeight = rectHeight; newWidth = (int)(newHeight * aspect); } } } var resizedImage = bitmap.Resize(new SKImageInfo(newWidth, newHeight), SKBitmapResizeMethod.Lanczos3); var image = resizedImage.Encode(SKEncodedImageFormat.Jpeg, 80); var path = System.Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData); var filepath = System.IO.Path.Combine(path, fileName); string finalPath = filepath; using (var stream = File.OpenWrite(filepath)) image.SaveTo(stream); return finalPath; } 我检查了你的代码，并通过不同的方式进行了实验，最后，我明白了为什么它会滞后。通过添加滚动视图，还记得修复图像的宽度。你能试试这个代码吗： <Grid BackgroundColor="#00aeef"> <Grid.RowDefinitions> <RowDefinition Height="*"/> </Grid.RowDefinitions> <scrollview> <CollectionView x:Name="myCollectionView" Grid.Row="0"> <CollectionView.ItemTemplate> <DataTemplate> <StackLayout> <Frame Padding="0" BackgroundColor="#00d2ff" Margin="20" CornerRadius="30"> <StackLayout Padding="20"> <Label Text="{Binding Airline}" TextColor ="White" FontSize="30" HorizontalOptions="Center"/> <Image Source="{Binding Url}" HeightRequest="200" WidthRequest="200"/> <Label Text="{Binding Plane, StringFormat='Plane: {0}'}" TextColor ="White" FontSize="15"/> <Label Text="{Binding Airline, StringFormat='Airline: {0}'}" TextColor ="White" FontSize="15"/> <Label Text="{Binding Livery, StringFormat='Livery: {0}'}" TextColor ="White" FontSize="15"/> <Label Text="{Binding Registration, StringFormat='Reg: {0}'}" TextColor ="White" FontSize="15"/> <Label Text="{Binding Airport, StringFormat='Airport: {0}'}" TextColor ="White" FontSize="15"/> <Label Text="{Binding Date, StringFormat='Date: {0}'}" TextColor ="White" FontSize="15"/> <Label Text="{Binding Comment, StringFormat='Comment: {0}'}" TextColor ="White" FontSize="15"/> </StackLayout> </Frame> </StackLayout> </DataTemplate> </CollectionView.ItemTemplate> </CollectionView> </scrollview> </Grid>

c# image xamarin lag collectionview

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尝试使用列中先前的值在 R 中执行计算

使用下面的数据框作为我想要做的粗略示例，在 b 列中，当 times = 0 时，我有正确的值，但我想对其进行编码，以便当前空白的值将使用 va。 ..

r lag

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