ios - autoreleasepool 和带 ARC 的池排水

Question

我想用 ARC 迁移这段代码。

我知道我必须使用:

@autoreleasepool {}

但是我的两个pool drain有问题，不知道怎么办。

- (void)downloadImageToCache:(NSString*)_urlImage
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    if (!(_urlImage) || (_urlImage == nil)) 
    {
        [pool drain];
        return;
    }

    NSURL *url = [NSURL URLWithString:_urlImage];
    NSData *data = [[[NSData alloc] initWithContentsOfURL:url] autorelease];

    if (data != nil) 
    {
        ...do something...
    }
    else
    {

        ...do something...
    }
    [pool drain];
}

Answer 1

包装整个东西。不用担心返回。它会弄明白的。

即编译器会将其转换为逻辑上等效的:(或者您可以显式清理逻辑)

- (void)downloadImageToCache:(NSString*)_urlImage
{
  NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

  if (!(_urlImage) || (_urlImage == nil))
  {
    //[pool drain];
    //return;
  } else {

    NSURL *url = [NSURL URLWithString:_urlImage];
    NSData *data = [[[NSData alloc] initWithContentsOfURL:url] autorelease];

    if (data != nil)
    {
      ...do something...
    }
    else
    {  
      ...do something...
    }
  }
  [pool drain];
}

减少为:

- (void)downloadImageToCache:(NSString*)_urlImage {
  @autoreleasepool {
    if (_urlImage != nil) {

      NSURL *url = [NSURL URLWithString:_urlImage];
      NSData *data = [[[NSData alloc] initWithContentsOfURL:url] autorelease];

      if (data != nil) {
        // ...do something...
      } else {
        //...do something...
      }
    }
  }
}

或者(较少的嵌套缩进总是我的偏好):

- (void)downloadImageToCache:(NSString*)_urlImage {
  if (_urlImage == nil) {
    NSLog(@"[%@ %@] Error Message", NSStringFromClass([self class]), NSStringFromSelector(_cmd));
    return;
  }

  @autoreleasepool {

    NSURL *url = [NSURL URLWithString:_urlImage];
    NSData *data = [[[NSData alloc] initWithContentsOfURL:url] autorelease];

    if (data != nil) {
      // ...do something...
    } else {
      //...do something...
    }
  }
}