无法将NSNumber更改为Double，并使用它进行一些计算

问题描述

我的问题是我有一个数组保存一些双重值

  NSArray * level4results = [context executeFetchRequest ：请求错误：& error]; 
  

然后我总结该数组中的所有值

  NSNumber * l4sum = [level4results valueForKeyPath：@sum.self]; 
  

接下来我想做的是将数组的总和除以8这是我被卡住的地方。我尝试了许多选项和方式，通过我不断得到不同的错误。这是我现在在我的代码中

  double l4average =（[l4sum doubleValue] / 8）; 
  

但是这是抛出以下错误

原因：' - [__ NSArrayI doubleValue]：
无法识别的选择器发送到实例

帮助解决这个问题赞赏。谢谢

解决方案

这是集合操作符。这行：

应写入：

NSNumber * l4sum = [level4results valueForKeyPath：@@ sum.self];

my problem is that i have an Array that holds some double values

NSArray *level4results = [context executeFetchRequest:request error:&error];

then i sum up all the values in that array

NSNumber *l4sum = [level4results valueForKeyPath:@"sum.self"];

The next thing i want to do is to divide by 8 the sum of the array... and this is where i am stuck. I have tried many options and ways of doing it by either way i kept on getting different error. This is what i have currently in my code

double l4average = ([l4sum doubleValue] / 8);

however this is throwing following error

Help in solving this problem appreciated. Thanks

解决方案

It's the collection operator. This line:

Should be written:

NSNumber *l4sum = [level4results valueForKeyPath:@"@sum.self"];

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