为什么是NULL? [英] Why is this NULL?

问题描述

谁能告诉我为什么这是NULL?

因此Array1是NSMutable，并且在索引0处具有NSString对象"UserName"；

  NSLog(@"array1％@的内容"，[array1 objectAtIndex:0])；//打印用户名 

现在，我这样做...

array2属于另一个类.我引用该类，导入.h文件，并添加属性并对其进行合成.

  [object2.array2 addObject:array1];//array2是NSMutable，可以在init方法的相应类中正确初始化NSLog(@"array2％@的内容，[object2.array2 objectAtIndex:0])；//打印(空)tempArray = [[NSMutableArray alloc] init];tempArray = [object2.array2 objectAtIndex:0];NSLog(@％@"，[tempArray objectAtIndex:0])；//打印(空)//应该是UserName 

添加更多信息:

object2 是另一个类的对象(这是 NSObject 的子类)，而object2包含array2作为其属性.

object2为零.为什么 ?如何??

解决方案

  NSLog(@"array2的内容％@"，[object2.array2 objectAtIndex:0])；//输出NULL 

如果打印为NULL"，则是以下四个原因之一:

• object2 为零
• object2.array2 返回nil
• 索引为0的对象是字符串"NULL"
• 索引0的 description 方法中的对象返回字符串"NULL"

是哪个?

---

对象2为零.我不知道为什么.

最有可能是因为您没有首先对其进行初始化.显示您的初始化代码，并删除一条日志语句或断点，并确保它实际上已在执行.

Can anyone tell me why this is NULL ?

So Array1 is NSMutable, and has an NSString object "UserName" at index 0;

NSLog (@"Contents of array1 %@", [array1 objectAtIndex:0]); //prints UserName

Now , I do this...

array2 belongs to another class. I reference the class, import .h file, and add property and synthesize it.

[object2.array2  addObject: array1]; //array2 is NSMutable properly initialized in it's respective class in the init method

NSLog (@"Contents of array2 %@", [object2.array2 objectAtIndex:0]); //prints (null)

tempArray = [[NSMutableArray alloc] init];
tempArray = [object2.array2 objectAtIndex:0];
NSLog (@"%@", [tempArray objectAtIndex:0]); // Prints (null) // Should be UserName

Adding more information:

object2 is an object of another class (which is a subclass of NSObject), and object2 contains array2 as it's property.

object2 is nil. WHY ? HOW ??

解决方案

NSLog (@"Contents of array2 %@", [object2.array2 objectAtIndex:0]); //prints NULL

If that 'prints NULL', then it is for one of four reasons:

• object2 is nil
• object2.array2 returns nil
• the object at index 0 is the string "NULL"
• the object at index 0's description method returns the string "NULL"

Which is it?

---

object 2 is nil. I wonder why.

Most likely because you didn't initialize it in the first place. Show your initialization code and also drop a log statement or breakpoint and make sure it is actually being executed.

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