Images

2023-01-22 03:30| 来源: 网络整理| 查看: 265

Images Article 12/23/2022 4 minutes to read

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.NET Multi-platform App UI (.NET MAUI) graphics includes functionality to load, save, resize, and downsize images. Supported image formats are dependent on the underlying platform.

Images are represented by the IImage type, which defines the following properties:

Width, of type float, that defines the width of an image. Height, of type float, that defines the height of an image.

An optional ImageFormat argument can be specified when loading and saving images. The ImageFormat enumeration defines Png, Jpeg, Gif, Tiff, and Bmp members. However, this argument is only used when the image format is supported by the underlying platform.

Note

.NET MAUI contains two different IImage interfaces. Microsoft.Maui.Graphics.IImage is used for image display, manipulation, and persistence in when displaying graphics in a GraphicsView. Microsoft.Maui.IImage is the interface that abstracts the Image control.

Load an image

Image loading functionality is provided by the GraphicsService class. Images can be loaded from a stream by the LoadFromStream method, or from a byte array using the LoadImageFromBytes method.

The following example shows how to load an image:

using Microsoft.Maui.Graphics.Platform; ... IImage image; Assembly assembly = GetType().GetTypeInfo().Assembly; using (Stream stream = assembly.GetManifestResourceStream("GraphicsViewDemos.Resources.Images.dotnet_bot.png")) { image = PlatformImage.FromStream(stream); } if (image != null) { canvas.DrawImage(image, 10, 10, image.Width, image.Height); }

Warning

The PlatformImage type isn't supported on Windows.

In this example, the image is retrieved from the assembly, loaded as a stream, and displayed.

Important

Loading an image that's embedded in an assembly requires the image to have its build action set to Embedded Resource rather than MauiImage.

Resize an image

Images can be resized using the IImage.Resize method, which requires width and height arguments, of type float, which represent the target dimensions of the image. The Resize method also accepts two optional arguments:

A ResizeMode argument, that controls how the image will be resized to fit its target dimensions. A bool argument that controls whether the source image will be disposed after performing the resize operation. This argument defaults to false, indicating that the source image won't be disposed.

The ResizeMode enumeration defines the following members, which specify how to resize the image to the target size:

Fit, which letterboxes the image so that it fits its target size. Bleed, which clips the image so that it fits its target size, while preserving its aspect ratio. Stretch, which stretches the image so it fills the available space. This can result in a change in the image aspect ratio.

The following example shows how to resize an image:

using Microsoft.Maui.Graphics.Platform; ... IImage image; Assembly assembly = GetType().GetTypeInfo().Assembly; using (Stream stream = assembly.GetManifestResourceStream("GraphicsViewDemos.Resources.Images.dotnet_bot.png")) { image = PlatformImage.FromStream(stream); } if (image != null) { IImage newImage = image.Resize(100, 60, ResizeMode.Stretch, true); canvas.DrawImage(newImage, 10, 10, newImage.Width, newImage.Height); }

Warning

The PlatformImage type isn't supported on Windows.

In this example, the image is retrieved from the assembly and loaded as a stream. The image is resized using the Resize method, with its arguments specifying the new size, and that it should be stretched to fill the available space. In addition, the source image is disposed. The resized image is then drawn at actual size at (10,10).

Downsize an image

Images can be downsized by one of the IImage.Downsize overloads. The first overload requires a single float value that represents the maximum width or height of the image, and downsizes the image while maintaining its aspect ratio. The second overload requires two float arguments, that represent the maximum width and maximum height of the image.

The Downsize overloads also accept an optional bool argument that controls whether the source image should be disposed after performing the downsizing operation. This argument defaults to false, indicating that the source image won't be disposed.

The following example shows how to downsize an image:

using Microsoft.Maui.Graphics.Platform; ... IImage image; Assembly assembly = GetType().GetTypeInfo().Assembly; using (Stream stream = assembly.GetManifestResourceStream("GraphicsViewDemos.Resources.Images.dotnet_bot.png")) { image = PlatformImage.FromStream(stream); } if (image != null) { IImage newImage = image.Downsize(100, true); canvas.DrawImage(newImage, 10, 10, newImage.Width, newImage.Height); }

Warning

The PlatformImage type isn't supported on Windows.

In this example, the image is retrieved from the assembly and loaded as a stream. The image is downsized using the Downsize method, with the argument specifying that its largest dimension should be set to 100 pixels. In addition, the source image is disposed. The downsized image is then drawn at actual size at (10,10).

Save an image

Images can be saved by the IImage.Save and IImage.SaveAsync methods. Each method saves the IImage to a Stream, and enables optional ImageFormat and quality values to be specified.

The following example shows how to save an image:

using Microsoft.Maui.Graphics.Platform; ... IImage image; Assembly assembly = GetType().GetTypeInfo().Assembly; using (Stream stream = assembly.GetManifestResourceStream("GraphicsViewDemos.Resources.Images.dotnet_bot.png")) { image = PlatformImage.FromStream(stream); } // Save image to a memory stream if (image != null) { IImage newImage = image.Downsize(150, true); using (MemoryStream memStream = new MemoryStream()) { newImage.Save(memStream); } }

Warning

The PlatformImage type isn't supported on Windows.

In this example, the image is retrieved from the assembly and loaded as a stream. The image is downsized using the Downsize method, with the argument specifying that its largest dimension should be set to 150 pixels. In addition, the source image is disposed. The downsized image is then saved to a stream.

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