WPF 将图像作为缩略图加载的方法

本教程转载自微软官网，示例演示如何将 Image 作为缩略图加载以节省应用程序内存。适用于图片列表等功能的优化。

在 XAML 中设置 DecodePixelWidth 属性

以下示例在 Extensible Application Markup Language (XAML) 中设置 BitmapImage 的 DecodePixelWidth 属性，以减少加载图像所需的内存。

<!-- Simple image rendering. However, rendering an image this way may not
     result in the best use of application memory. See markup below which
     creates the same end result but using less memory. -->
<Image Width="200" 
Source="C:\Documents and Settings\All Users\Documents\My Pictures\Sample Pictures\Water Lilies.jpg"/>

<Image Width="200">
  <Image.Source>
    <!-- To save significant application memory, set the DecodePixelWidth or  
     DecodePixelHeight of the BitmapImage value of the image source to the desired 
     height and width of the rendered image. If you don't do this, the application will 
     cache the image as though it were rendered as its normal size rather than just 
     the size that is displayed. -->
    <!-- Note: In order to preserve aspect ratio, only set either DecodePixelWidth
         or DecodePixelHeight but not both. -->
    <BitmapImage DecodePixelWidth="200"  
     UriSource="C:\Documents and Settings\All Users\Documents\My Pictures\Sample Pictures\Water Lilies.jpg" />
  </Image.Source>
</Image>

在代码中设置 DecodePixelWidth 属性

以下示例在代码中设置 BitmapImage 的 DecodePixelWidth 属性，以减少加载图像所需的内存。

// Create Image Element
Image myImage = new Image();
myImage.Width = 200;

// Create source
BitmapImage myBitmapImage = new BitmapImage();

// BitmapImage.UriSource must be in a BeginInit/EndInit block
myBitmapImage.BeginInit();
myBitmapImage.UriSource = new Uri(@"C:\Documents and Settings\All Users\Documents\My Pictures\Sample Pictures\Water Lilies.jpg");

// To save significant application memory, set the DecodePixelWidth or
// DecodePixelHeight of the BitmapImage value of the image source to the desired
// height or width of the rendered image. If you don't do this, the application will
// cache the image as though it were rendered as its normal size rather than just
// the size that is displayed.
// Note: In order to preserve aspect ratio, set DecodePixelWidth
// or DecodePixelHeight but not both.
myBitmapImage.DecodePixelWidth = 200;
myBitmapImage.EndInit();
//set image source
myImage.Source = myBitmapImage;

实际测试发现，一张分辨率为 7360 x 4912 的图片。直接展示启动后的程序内存占用 534 MB，通过上述方法生成缩略图后，内存占用降低为 65 MB，效果非常明显。