removeObjectAtIndex導致「消息發送到解除分配的實例」

Question

我將一些代碼轉換爲ARC。代碼在NSMutableArray中搜索一個元素，然後找到，移除並返回該元素。問題是，該元素能夠順利通過「removeObjectAtIndex」立即釋放：

- (UIView *)viewWithTag:(int)tag 
{ 
    UIView *view = nil; 
    for (int i = 0; i < [self count]; i++) 
    { 
     UIView *aView = [self objectAtIndex:i]; 
     if (aView.tag == tag) 
     { 
      view = aView; 
      NSLog(@"%@",view); // 1 (view is good) 
      [self removeObjectAtIndex:i]; 
      break; 
     } 
    } 
    NSLog(@"%@",view); // 2 (view has been deallocated) 
    return view; 
} 

當我運行它，我得到

*** -[UIView respondsToSelector:]: message sent to deallocated instance 0x87882f0 

在第二日誌語句。

Pre-ARC，我在調用removeObjectAtIndex之前小心的保留了對象，然後自動釋放它。我如何告訴ARC做同樣的事情？

Answer 1

聲明UIView *view參考與__autoreleasing預選賽中，像這樣：

- (UIView *)viewWithTag:(int)tag 
{ 
    __autoreleasing UIView *view; 
    __unsafe_unretained UIView *aView; 

    for (int i = 0; i < [self count]; i++) 
    { 
     aView = [self objectAtIndex:i]; 
     if (aView.tag == tag) 
     { 
      view = aView; 
      //Since you declared "view" as __autoreleasing, 
      //the pre-ARC equivalent would be: 
      //view = [[aView retain] autorelease]; 

      [self removeObjectAtIndex:i]; 
      break; 
     } 
    } 

    return view; 
} 

__autoreleasing會給你正是你想要什麼，因爲在分配新指針對象被保留，自動釋放，然後存儲到左翼。

見ARC reference