为图像网格创建缩略图

发布于 2024-11-04 01:17:43 字数 227 浏览 0 评论 0原文

我正在构建一个应用程序，例如 iPad 上苹果的照片应用程序。我有一个大的全屏图像，我使用滚动视图来显示它们来管理缩放和分页。当我尝试使用图像缩略图创建网格时，出现了主要问题。我将它们创建为重叠在 UIButton 上的 UIImageView。一切都很好，但是当我在 iPad 上尝试该应用程序时，它需要大量内存，我想这取决于图像的重新缩放。有没有一种方法可以用小图像创建 UIImageView，重新缩放较大的图像，而不使用那么多内存？

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为人所爱 2024-11-11 01:17:43

您可以使用 UIGraphics 创建缩略图。这是执行此操作的代码：

UIGraphicsBeginImageContext(CGSizeMake(length, length));
CGContextRef currentContext = UIGraphicsGetCurrentContext();
CGContextClipToRect( currentContext, clippedRect);
CGFloat scaleFactor = length/sideFull;
if (widthGreaterThanHeight) {
    //a landscape image – make context shift the original image to the left when drawn into the context
    CGContextTranslateCTM(currentContext, -((mainImage.size.width - sideFull) / 2) * scaleFactor, 0);
}
else {
    //a portfolio image – make context shift the original image upwards when drawn into the context
    CGContextTranslateCTM(currentContext, 0, -((mainImage.size.height - sideFull) / 2) * scaleFactor);
}
//this will automatically scale any CGImage down/up to the required thumbnail side (length) when the CGImage gets drawn into the context on the next line of code
CGContextScaleCTM(currentContext, scaleFactor, scaleFactor);
[mainImageView.layer renderInContext:currentContext];
UIImage* thumbnail = UIGraphicsGetImageFromCurrentImageContext();

You can use UIGraphics to create a thumbnail. Here's this code to do it:

UIGraphicsBeginImageContext(CGSizeMake(length, length));
CGContextRef currentContext = UIGraphicsGetCurrentContext();
CGContextClipToRect( currentContext, clippedRect);
CGFloat scaleFactor = length/sideFull;
if (widthGreaterThanHeight) {
    //a landscape image – make context shift the original image to the left when drawn into the context
    CGContextTranslateCTM(currentContext, -((mainImage.size.width - sideFull) / 2) * scaleFactor, 0);
}
else {
    //a portfolio image – make context shift the original image upwards when drawn into the context
    CGContextTranslateCTM(currentContext, 0, -((mainImage.size.height - sideFull) / 2) * scaleFactor);
}
//this will automatically scale any CGImage down/up to the required thumbnail side (length) when the CGImage gets drawn into the context on the next line of code
CGContextScaleCTM(currentContext, scaleFactor, scaleFactor);
[mainImageView.layer renderInContext:currentContext];
UIImage* thumbnail = UIGraphicsGetImageFromCurrentImageContext();

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