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。
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。
这是我的 UIImageView 扩展:
@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 = [[NSData alloc] initWithContentsOfFile:path];
UIImage * original = [[[UIImage alloc] initWithData:imgData] autorelease];
[imgData release];
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 = [[UIImage alloc] initWithCGImageriginal.CGImage scale:1/scaleFactor orientationriginal.imageOrientation];
} else {
result = [original retain];
}
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;
[result release];
[[NSNotificationCenter defaultCenter] postNotificationName:NTF_IMG_LOADED object:self];
NSLog(@"Updated");
});
});
dispatch_release(queue);
}
@end
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。
在 iOS 上显示大型本地镜像的正确方法是什么?
应用程序是为 iOS5+ 构建的..
谢谢,
Best Answer-推荐答案 strong>
您实际上并没有调整图像的大小。 -initWithCGImage:scale: 的scale 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 CGContext 以缩小它:
//Load image
UIImage * original = [[[UIImage alloc] 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);
[original drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
result = UIGraphicsGetImageFromCurrentImageContext();
[result retain];
UIGraphicsEndImageContext();
} else {
result = [original retain];
}
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:
https://stackoverflow.com/questions/15852820/
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