ios - UIImageView 性能不佳(用于本地镜像)
<p><p>我正在开发一个带有图库的应用程序。
所有图像都在设备光盘(文档目录)上,但我无法顺利显示。 </p>
<p>由于有些图像很大(2000px * 2000px),我将它们加载到后台线程中,然后缩小它们,然后将它们显示在主线程上。</p>
<p>这是我的 UIImageView 扩展:</p>
<pre><code>@implementation UIImageView (BackgroundResize)
- (void)localImageFromPath: (NSString *) path scaledTo: (CGSize) size {
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0);
dispatch_async(queue, ^{
//Load image
NSData * imgData = [ initWithContentsOfFile:path];
UIImage * original = [[initWithData:imgData] autorelease];
;
CGSize imgSize = original.size;
float widthScale = size.width / imgSize.width;
float heightScale = size.height / imgSize.height;
float scaleFactor = widthScale;
if (heightScale < scaleFactor) {
scaleFactor = heightScale;
}
UIImage * result = nil;
//Scale if necessary
if (scaleFactor < 1.0) {
result = [ initWithCGImage:original.CGImage scale:1/scaleFactor orientation:original.imageOrientation];
} else {
result = ;
}
NSLog(@"Image prepeared on backgroud thread, update ui image on main..");
dispatch_async(dispatch_get_main_queue(), ^{
NSLog(@"Begin updating image on main thread");
self.image = result;
;
[ postNotificationName:NTF_IMG_LOADED object:self];
NSLog(@"Updated");
});
});
dispatch_release(queue);
}
@end
</code></pre>
<p>在控制台输出中,一切似乎都很完美,所有调试字符串都在不到 1 秒的时间内显示(对于 6 个非常大的图像),但 UI 被阻止并且图像显示延迟 10 秒。 </p>
<p>在 iOS 上显示大型本地镜像的正确方法是什么? </p>
<p>应用程序是为 iOS5+ 构建的..</p>
<p>谢谢,</p></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><p>您实际上并没有调整图像的大小。 <code>-initWithCGImage:scale:</code>的<code>scale</code>参数设置图像像素与屏幕坐标点的比例;它对底层图像没有任何作用。您需要将图像实际绘制到 <code>CGContext</code> 以缩小它:</p>
<pre><code> //Load image
UIImage * original = [[ initWithContentsOfFile:path] autorelease];
CGSize imgSize = original.size;
float widthScale = size.width / imgSize.width;
float heightScale = size.height / imgSize.height;
float scaleFactor = widthScale;
if (heightScale < scaleFactor) {
scaleFactor = heightScale;
}
UIImage * result = nil;
//Scale if necessary
if (scaleFactor < 1.0) {
CGSize newSize = CGSizeMake(floorf(imgSize.width * scaleFactor),
floorf(imgSize.height * scaleFactor));
UIGraphicsBeginImageContextWithOptions(newSize, NO, 0);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetInterpolationQuality(context, kCGInterpolationHigh);
;
result = UIGraphicsGetImageFromCurrentImageContext();
;
UIGraphicsEndImageContext();
} else {
result = ;
}
</code></pre></p>
<p style="font-size: 20px;">关于ios - UIImageView 性能不佳(用于本地镜像),我们在Stack Overflow上找到一个类似的问题:
<a href="https://stackoverflow.com/questions/15852820/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/15852820/
</a>
</p>
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