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我有一個UIScrollView，它內部並排加載一組圖像。你可以在這裏看到我的應用程序的例子：http://www.42restaurants.com。我的問題出現在內存使用情況中。我想懶加載圖像，因爲它們即將出現在屏幕上，並卸載不在屏幕上的圖像。正如你可以在代碼中看到的，我至少需要加載哪個映像，然後將加載部分分配給NSOperation並將其放置在NSOperationQueue上。除了簡單的滾動體驗外，一切都很好。在UIScrollView中加載優化圖像
我不知道如果任何人有任何想法，我怎樣才能使這個更加優化，使每個圖像的加載時間最小化或使滾動不暢少。
- (void)scrollViewDidScroll:(UIScrollView *)scrollView{
[self manageThumbs];
}
- (void) manageThumbs{
int centerIndex = [self centerThumbIndex];
if(lastCenterIndex == centerIndex){
return;
}
if(centerIndex >= totalThumbs){
return;
}
NSRange unloadRange;
NSRange loadRange;
int totalChange = lastCenterIndex - centerIndex;
if(totalChange > 0){ //scrolling backwards
loadRange.length = fabsf(totalChange);
loadRange.location = centerIndex - 5;
unloadRange.length = fabsf(totalChange);
unloadRange.location = centerIndex + 6;
}else if(totalChange < 0){ //scrolling forwards
unloadRange.length = fabsf(totalChange);
unloadRange.location = centerIndex - 6;
loadRange.length = fabsf(totalChange);
loadRange.location = centerIndex + 5;
}
[self unloadImages:unloadRange];
[self loadImages:loadRange];
lastCenterIndex = centerIndex;
return;
}
- (void) unloadImages:(NSRange)range{
UIScrollView *scrollView = (UIScrollView *)[[self.view subviews] objectAtIndex:0];
for(int i = 0; i < range.length && range.location + i < [scrollView.subviews count]; i++){
UIView *subview = [scrollView.subviews objectAtIndex:(range.location + i)];
if(subview != nil && [subview isKindOfClass:[ThumbnailView class]]){
ThumbnailView *thumbView = (ThumbnailView *)subview;
if(thumbView.loaded){
UnloadImageOperation *unloadOperation = [[UnloadImageOperation alloc] initWithOperableImage:thumbView];
[queue addOperation:unloadOperation];
[unloadOperation release];
}
}
}
}
- (void) loadImages:(NSRange)range{
UIScrollView *scrollView = (UIScrollView *)[[self.view subviews] objectAtIndex:0];
for(int i = 0; i < range.length && range.location + i < [scrollView.subviews count]; i++){
UIView *subview = [scrollView.subviews objectAtIndex:(range.location + i)];
if(subview != nil && [subview isKindOfClass:[ThumbnailView class]]){
ThumbnailView *thumbView = (ThumbnailView *)subview;
if(!thumbView.loaded){
LoadImageOperation *loadOperation = [[LoadImageOperation alloc] initWithOperableImage:thumbView];
[queue addOperation:loadOperation];
[loadOperation release];
}
}
}
}
編輯： 感謝真正偉大的反應。這是我的NSOperation代碼和ThumbnailView代碼。我在週末嘗試了幾件事情，但我只設法通過在滾動期間暫停操作隊列並在滾動完成時恢復操作隊列來提高性能。
這裏是我的代碼片段：
//In the init method
queue = [[NSOperationQueue alloc] init];
[queue setMaxConcurrentOperationCount:4];
//In the thumbnail view the loadImage and unloadImage methods
- (void) loadImage{
if(!loaded){
NSString *filename = [NSString stringWithFormat:@"%03d-cover-front", recipe.identifier, recipe.identifier];
NSString *directory = [NSString stringWithFormat:@"RestaurantContent/%03d", recipe.identifier];
NSString *path = [[NSBundle mainBundle] pathForResource:filename ofType:@"png" inDirectory:directory];
UIImage *image = [UIImage imageWithContentsOfFile:path];
imageView = [[ImageView alloc] initWithImage:image andFrame:CGRectMake(0.0f, 0.0f, 176.0f, 262.0f)];
[self addSubview:imageView];
[self sendSubviewToBack:imageView];
[imageView release];
loaded = YES;
}
}
- (void) unloadImage{
if(loaded){
[imageView removeFromSuperview];
imageView = nil;
loaded = NO;
}
}
然後我的加載和卸載操作：
- (id) initWithOperableImage:(id<OperableImage>) anOperableImage{
self = [super init];
if (self != nil) {
self.image = anOperableImage;
}
return self;
}
//This is the main method in the load image operation
- (void)main {
[image loadImage];
}
//This is the main method in the unload image operation
- (void)main {
[image unloadImage];
}
謝謝你。我一定會看看。 – 2010-04-09 08:18:42