图像视图未在 NSThread 上更新

Question

我正在尝试制作一个测试应用程序来测量线程的性能。但是，我正在尝试在线程上将图像设置为 imageview 并且它没有更新。事实上，setImage1 和 setImage2 方法甚至都没有被调用。有任何想法吗？ 详情看代码

#import "UntitledAppDelegate.h"
#import <QuartzCore/QuartzCore.h>

@implementation UntitledAppDelegate

@synthesize window, imageView1, imageView2, label1, label2, label0;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 
{            
    [window makeKeyAndVisible];
    return YES;
}

-(IBAction) startSeparate:(id) sender
{
 imageView1.image = imageView2.image = nil;
 double prev;

    start = prev = CACurrentMediaTime(); 
 [self setImage1];
 label1.text = [NSString stringWithFormat:@"%.10g", CACurrentMediaTime() - prev];

 prev = CACurrentMediaTime();  
 [self setImage2];
 label2.text = [NSString stringWithFormat:@"%.10g", CACurrentMediaTime() - prev];
}

-(IBAction) startThreaded:(id) sender
{
 imageView1.image = imageView2.image = nil;
 double prev;

 NSThread *t1 = [[NSThread alloc] init];
 [t1 start];
 NSThread *t2 = [[NSThread alloc] init];
 [t2 start];

    start = prev = CACurrentMediaTime(); 
    //This doesn't work
    //[self performSelector:@selector(setImage1) onThread:t1 withObject:nil waitUntilDone:NO];

    //But this does
 [self performSelectorInBackground:@selector(setImage1) withObject:nil];

 label1.text = [NSString stringWithFormat:@"%.10g", CACurrentMediaTime() - prev];

 prev = CACurrentMediaTime();  
 //This doesn't work
    //[self performSelector:@selector(setImage2) onThread:t2 withObject:nil waitUntilDone:NO];

    //But this does
 [self performSelectorInBackground:@selector(setImage2) withObject:nil];

 label2.text = [NSString stringWithFormat:@"%.10g", CACurrentMediaTime() - prev];
}

-(void) setImage1
{
 NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
 UIImage *image1 = [UIImage imageNamed:@"bird.png"];
 imageView1.image = image1;
 [self pictureDone];
 [pool drain];
}

-(void) setImage2
{
 NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
 UIImage *image2 = [UIImage imageNamed:@"bird.png"];
 imageView2.image = image2;
 [self pictureDone];
 [pool drain];
}

-(void) pictureDone
{
 done++;
 NSLog(@"%i", done);
 if (done == 2) {
  label0.text = [NSString stringWithFormat:@"%.10g", CACurrentMediaTime() - start];
  done = 0;
 }
}
@end

Answer 1

永远不要从后台线程更改当前显示的 UIView 中的任何内容。您可能会遇到一百万种不同的同步问题。在后台线程中下载图片，然后在主线程（从后台线程）调用另一个方法来实际更新 UIImageView

performSelectorOnMainThread:...

至于方法没有运行的问题，试试这个吧：

[self performSelectorInBackground:@selector(setImage2:) withObject:nil];

（在setImage2之后添加一个冒号）。

另外，我认为这两个 NSThread 对象（t1 和 t2）不是必需的，它们也可能造成内存泄漏。

Answer 2

从技术上讲，NSThread 本身不会自动创建运行循环，那么如果您只是这样创建线程，performSelector:onThread 将无法工作。