我制作了一个函数，它获取原始图像并将其调整为 3 种不同的缩放比例 -> 16x、10x 和 4x。为了更好地理解，请继续阅读本段。假设原始图像是 1000x1000。我声明在 1 倍变焦时它的尺寸将为 50x50。这意味着 4 倍变焦将是 200x200，10 倍变焦将是 500x500，16 倍变焦将是 800x800。所以我的函数需要将原来的 1000x1000 缩小到 800x800，然后缩小到 500x500，然后缩小到 200x200。请注意，我已成功完成此操作，我的问题是关于内存使用情况。
下面我有两种方法。两种方法都有效，但是一种方法会导致巨大的内存使用膨胀，使用的内存大约是另一种方法的 3 倍/4 倍……我更喜欢第二种方法，因为它的加载速度比第一种方法快得多，因为它不会调整 3 幅图像中的每一个的大小从原始图像，而不是从以前调整大小的图像调整它们的大小。
注意：我正在使用 Xcode Instruments 来测量内存使用情况。ImageResizer 类包含一个名为“Resize”的函数，用于调整图像的大小。
方法1。）
public List<UIImage> InitImageList_BFObjects ( UIImage image, SizeF frameSize )
{
List<UIImage> listOfImages = new List<UIImage>();
for ( int i = 0; i < 3; i++ )
{
if ( i == 0 )
zoomScale = 16f;
else if ( i == 1 )
zoomScale = 10f;
else// if ( i == 2 )
zoomScale = 4f;
Resizer = new ImageResizer(image);
Resizer.Resize(frameSize.Width * zoomScale, frameSize.Height * zoomScale);
UIImage resizedImage = Resizer.ModifiedImage;
listOfImages.Insert(0, resizedImage);
}
return listOfImages;
}
方法 1 有效并且使用的内存非常少。我用一组大约 20 张图像运行了这个。加载后我的应用程序使用了大约 14mb 的内存（使用 Xcodes Instruments 检查内存使用情况）
方法2。）
public List<UIImage> InitImageList_BFObjects ( UIImage image, SizeF frameSize )
{
List<UIImage> listOfImages = new List<UIImage>();
for ( int i = 0; i < 3; i++ )
{
if ( i == 0 )
zoomScale = 16f;
else if ( i == 1 )
zoomScale = 10f;
else// if ( i == 2 )
zoomScale = 4f;
if ( listOfImages.Count == 0 )
{
Resizer = new ImageResizer(image);
Resizer.Resize(frameSize.Width * zoomScale, frameSize.Height * zoomScale);
UIImage resizedImage = Resizer.ModifiedImage;
listOfImages.Insert(0, resizedImage);
}
else
{
// THIS LINE CONTAINS THE MAIN DIFFERENCE BETWEEN METHOD 1 AND METHOD 2
// Notice how it resizes from the most recent image from listOfImages rather than the original image
Resizer = new ImageResizer(listOfImages[0]);
Resizer.Resize(frameSize.Width * zoomScale, frameSize.Height * zoomScale);
UIImage resizedImage = Resizer.ModifiedImage;
listOfImages.Insert(0, resizedImage);
}
}
return listOfImages;
}
方法 2 有效，但内存使用量猛增！我用同一组大约 20 张图像运行了这个。加载后我的应用程序有超过 60mb 的内存使用量（使用 Xcodes Instruments 检查内存使用情况）为什么内存使用量如此之高？方法二到底是怎么回事，导致内存一飞冲天？就好像一个变量没有被正确清理
* 附加信息，ImageResizer 类* *
我从 ImageResizer 类中删除了不需要的功能，并将其重命名为“ImageResizer_Abridged”。我什至转而使用这个类，以确保我没有不小心删掉任何需要的东西。
public class ImageResizer_Abridged
{
UIImage originalImage = null;
UIImage modifiedImage = null;
public ImageResizer_Abridged ( UIImage image )
{
this.originalImage = image;
this.modifiedImage = image;
}
/// <summary>
/// strech resize
/// </summary>
public void Resize( float width, float height )
{
UIGraphics.BeginImageContext( new SizeF( width, height ) );
//
modifiedImage.Draw( new RectangleF( 0,0, width, height ) );
modifiedImage = UIGraphics.GetImageFromCurrentImageContext();
//
UIGraphics.EndImageContext();
}
public UIImage OriginalImage
{
get
{
return this.originalImage;
}
}
public UIImage ModifiedImage
{
get
{
return this.modifiedImage;
}
}
}
我创建了一个显示此问题的简化测试项目*
这是该项目的保管箱链接： https ://www.dropbox.com/s/4w7d87nn0aafph9/TestMemory.zip
这是方法 1 的 Xcode Instruments 屏幕截图作为证据（9 mb 内存使用）：http: //i88.photobucket.com/albums/k194/lampshade9909/AllImagesResizedFromOriginalImage_zps585228c6.jpg
这是方法 2 的 Xcode Instruments 屏幕热作为证据（55 mb 内存使用）：http: //i88.photobucket.com/albums/k194/lampshade9909/SignificantIncreaseInMemoryUsage_zps19034bad.jpg
下面是运行测试项目所需的代码块
// Initialize My List of Images
ListOfImages = new List<UIImage>();
for ( int i = 0; i < 30; i++ )
{
// Create a UIImage Containing my original Image
UIImage originalImage = UIImage.FromFile ("b2Bomber.png");
float newWidth = 100f;
float newHeight = 40f;
float zoomScale;
float resizedWidth, resizedHeight;
UIImage resizedImage1;
UIImage resizedImage2;
// Basically, I want to take the originalImage Image and resize it twice.
// Method 1.) Resize the originalImage and save it as ResizedImage1. Resize the originalImage and save it as ResizedImage2. We're finished!
// Method 2.) Resize the originalImage and save it as ResizedImage1. Resize ResizedImage1 and save it as ResizedImage2. We're finished!
// The pro to Method 1 is that we get the best possible quaility on all resized images. The con is, this takes a long time if we're doing dozens of very large images
// The pro to Method 2 is that it's faster than Method 1. This is why I want to use Method 2, it's speed. But it has a HUGE con, it's memory usage.
// Please run this project on an iPad connected to XCodes Instruments to monitor memory usage and see what I mean
zoomScale = 10f;
resizedWidth = newWidth*zoomScale;
resizedHeight = newHeight*zoomScale;
UIGraphics.BeginImageContext( new SizeF( resizedWidth, resizedHeight ) );
originalImage.Draw( new RectangleF( 0, 0, resizedWidth, resizedHeight ) );
resizedImage1 = UIGraphics.GetImageFromCurrentImageContext();
UIGraphics.EndImageContext();
zoomScale = 4f;
resizedWidth = newWidth*zoomScale;
resizedHeight = newHeight*zoomScale;
UIGraphics.BeginImageContext( new SizeF( resizedWidth, resizedHeight ) );
// Run this project on an iPad and examine the memory usage in XCode's Instruments.
// The Real Memory Usage will be aroud 9 MB.
// Uncomment this "originalImage.Draw" line to see this happening, make sure to comment out the "resizedImage1.Draw" line
// originalImage.Draw( new RectangleF( 0, 0, resizedWidth, resizedHeight ) );
// Run this project on an iPad and examine the memory usage in XCode's Instruments.
// The Real Memory Usage will be aroud 55 MB!!
// My question is, why does the memory sky rocket when doing this, and how can I prevent the memory from sky rocketing??
// My App requires me to resize around a hundred images and I want to be able to resize an already resized image (like in this example) without the memory usage sky rocketing like this...
// Uncomment this "resizedImage1.Draw" line to see this happening, make sure to comment out the "originalImage.Draw" line
resizedImage1.Draw( new RectangleF( 0, 0, resizedWidth, resizedHeight ) );
resizedImage2 = UIGraphics.GetImageFromCurrentImageContext();
UIGraphics.EndImageContext();
// Add my resized images to the list of Images
ListOfImages.Add (resizedImage1);
ListOfImages.Add (resizedImage2);
}