objective-c - 使用 ARC 保留/释放正在减慢我的速度

Question

我在我的 iOS 应用程序中使用 ARC。我已经分析了下面的方法，尽管该算法非常幼稚和浪费，但 77% 的时间花在了 objc_retain 和 objc_release 上。我认为这一定是我从 NSArray 中获取一个 Unit 并且 ARC 每次都小心地保留然后释放该对象的那一行。

我正在寻找明智的建议:如何优雅地修复它？

-(CGFloat)getUncertaintyForUnits:(NSArray*)units Position:(MKMapPoint)position Zoom:(MKZoomScale)zoomScale {

    CGFloat closest = MAXFLOAT; 

    for (int i = 0; i < [units count]; i++) {
        Unit *units = (Unit*)[units objectAtIndex:i];

        CGFloat distance = [self distanceBetweenMapPoints:unit.mapPoint And:position];

        if (distance < closest) {
            closest = distance;
        }
    }

    CGFloat max = 100 / zoomScale;
    return  (1. - closest / max) * 0.9;
}

Answer 1

你可以试试fast enumeration :

for (Unit *unit in units) {
    CGFloat distance = [self distanceBetweenMapPoints:unit.mapPoint And:position];
    if (distance < closest) {
        closest = distance;
    }
}

这应该避免额外的保留/释放，因为在快速枚举中整个数组都被阻塞了。

There are several advantages to using fast enumeration:

• The enumeration is considerably more efficient than, for example, using NSEnumerator directly.
• The syntax is concise.
• Enumeration is “safe”—the enumerator has a mutation guard so that if you attempt to modify the collection during enumeration, an exception is raised.