objectForKey null检查

试图检查项目中的数据的有效性（项目是NSDictionary ）

我认为这应该工作，但我进入第二个，如果和崩溃：
unrecognized selector sent to instance galleryArr是(null)

  NSArray *galleryArr = [item objectForKey:@"photos"]; if (galleryArr != nil ) { if ([galleryArr count] != 0) { //do something } } 

有任何想法吗？

Answer 1

添加一个检查[gallryArr isKindOfClass:[NSArray class]] 。

Answer 2

我用一个简单的Objective-C类来解决这个问题：

的NSDictionary + NotNull.h

 #import <Foundation/Foundation.h> /*! This category extends NSDictionary to work around an issue with NSNull object. */ @interface NSDictionary (NotNull) /*! @abstract Returns the value associated with a given key, but only if the value is not NSNull. @param aKey The key for which to return the corresponding value. @return The value associated with the given key, or nil if no value is associated with the key, or the value is NSNull. */ - (id)objectOrNilForKey:(id)aKey; @end 

的NSDictionary + NotNull.m

 #import "NSDictionary+NotNull.h" @implementation NSDictionary (NotNull) - (id)objectOrNilForKey:(id)aKey { id object = [self objectForKey:aKey]; if (object == [NSNull null]) { return nil; } return object; } @end 

现在你可以打电话给：

 NSArray *galleryArr = [item objectOrNilForKey:@"photos"]; 

Answer 3

也许你会得到NSNull ？ 这是一个单独的（ [NSNull null] ）对象，代表零。 你可以检查if([gallryArr isKindOfClass:[NSArray class]]) 。