检查NSDictionary中是否存在密钥为null [英] Check if key exists in NSDictionary is null or not

问题描述

我确实搜索了如何检查NSDictionary密钥是否存在，并提出了解决方案。但它仍然会给我一个错误，即向键添加空值。
我不确定我的代码是否正确。如果有人对此有任何想法可以帮助我。

I did search on how to check if NSDictionary key exists or not and came up with the solution. But still it throws me an error saying adding null value to the key. I am not sure if my code is correct or not. If anyone has any idea about this can help me.

NSDictionary *result;
id myImageURL = [result objectForKey:@"url"];
if ((NSNull *)myImageURL == [NSNull null])
    myImageURL = @"";

id myImage = [result objectForKey:@"image"];
if ((NSNull *)myImage == [NSNull null])
    myImage = @"";

检查null是否添加任何内容，如果没有添加值。但它仍然给我一个错误，不知道为什么。

Check if null add nothing and if not add the value. But it still gives me an error dont know why.

/****OUTPUT*****/

2011-08-11 14:56:06.668 Tab_Table_Win[6510:207] RESULTS : {
image = "<UIImage: 0xbc332c0>";
url = "http://a3.twimg.com/profile_images/999228511/normal.jpg";
}

2011-08-11 14:56:06.669 Tab_Table_Win[6510:207] url : http://a3.twimg.com/profile_images/999228511/normal.jpg
2011-08-11 14:56:06.670 Tab_Table_Win[6510:207] IMage : <UIImage: 0xbc332c0>

/*****Breaks Here ***/

2011-08-11 14:56:06.876 Tab_Table_Win[6510:207] RESULTS : {
}
2011-08-11 14:56:06.878 Tab_Table_Win[6510:207] url : (null)
2011-08-11 14:56:06.879 Tab_Table_Win[6510:207] IMage : (null)
2011-08-11 14:56:06.881 Tab_Table_Win[6510:207] *** Terminating app due to uncaught    exception 'NSInvalidArgumentException', reason: '-[__NSCFDictionary setObject:forKey:]: attempt to insert nil key'

推荐答案

正确答案是：

NSDictionary *result;
NSURL *myImageURL = [result objectForKey:@"url"];
UIImage *myImage = [result objectForKey:@"image"];

/**** Correct way ****/
if (myImageURL != nil && myImage != nil) {
    [images setObject:myImage forKey:myImageURL];
}

感谢您提供所有解释。

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