ios 检查 NSDictionary 是否为空
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Check if NSDictionary is empty
提问by Steaphann
I want to check if an NSDictionaryis empty. I am doing it like this.
我想检查 anNSDictionary是否为空。我正在这样做。
mutDictValues = [[[NSUserDefaults standardUserDefaults] objectForKey:@"dicValues"]mutableCopy];
NSLog(@"dictValues are %@",mutDictValues);
if(mutDictValues == NULL){
arrCities = [[NSMutableArray alloc]init];
NSLog(@"no cities seleceted");
}else{
arrCities = [[NSMutableArray alloc]init];
arrCities = [mutDictValues objectForKey:@"cities"];
[self placeCities];
}
But it alwasy crashes on this line arrCities = [mutDictValues objectForKey:@"cities"];with the following error:
但它总是在这条线上崩溃arrCities = [mutDictValues objectForKey:@"cities"];并出现以下错误：
-[__NSCFConstantString objectForKey:]:
Can someone help me with this ?
有人可以帮我弄这个吗 ？
回答by Balu
While retrieving the dictionary values from NSUserDefaults that dictionary automatically converted into string that is the reason for getting crashed and for checking dictionary use
[dictionary count];
从 NSUserDefaults 检索字典值时，该字典自动转换为字符串，这是崩溃和检查字典使用的原因
[dictionary count];
EDIT:- use dictionaryForKey: method
编辑：-使用dictionaryForKey：方法
NSDictionary *dict =[[NSDictionary alloc]initWithObjectsAndKeys:@"hi",@"one",nil];
[[NSUserDefaults standardUserDefaults] setObject:dict forKey:@"dic"];
NSDictionary *dictn = [[NSUserDefaults standardUserDefaults] dictionaryForKey:@"dic"];
NSLog(@"%@",[dictn objectForKey:@"one"]);
回答by rashii
if ( [mutDictValues count] == 0 ) {
//code here
}
else {
//code here
}
After having your dic retrieved this should do
取回你的 dic 后，这应该做
回答by βhargav?
try this,
尝试这个，
if([myDict count] > 0)
NSLog(@"Dictionary is not empty");
else
NSLog(@"Dictionary is empty");
回答by vikingosegundo
Somewhere you treat a nsstring (a concrete subclass) as NSdictionary.
在某个地方，您将 nsstring（一个具体的子类）视为 NSdictionary。
回答by Aadil Keshwani
I had a bit different issue but it is related so i would like to share it here.
我有一个有点不同的问题，但它是相关的，所以我想在这里分享。
I was fetching the webservices & storing data in NSDictionary & again Fetching objectForKey which was Null. So the solution i found is as under
我正在获取网络服务并在 NSDictionary 中存储数据，然后再次获取为 Null 的 objectForKey。所以我找到的解决方案如下
NSMutableDictionary *result = [NSJSONSerialization JSONObjectWithData:[str dataUsingEncoding:NSUTF8StringEncoding] options:0 error:nil];
// NSLog(@"%@" , result);
NSMutableDictionary *sup = [result objectForKey:@"keysupplied"];
NSNull *n=[NSNull null];
if ( sup ! = n ){
//Your code if its not null
}
The reason behind using NSNull was it was returning (NSNull *) when i debugged the application So i finally figured out this way.
使用 NSNull 的原因是当我调试应用程序时它正在返回 (NSNull *) 所以我终于想通了这种方式。
回答by William Falcon
BOOL containsKeyABC = [myDict: valueForKey:@"ABC"];
int items = dict.count;
if (items > 0) {
//not empty
}
回答by Waseem Shah
try this code
试试这个代码
NSMutableDictionary *dict = ...
BOOL isEmpty = ([dict count] == 0);
回答by Amar
As most of the answers have correctly pointed out that you are passing un-recognized selector objectForKey:to a NSStringinstance instead of NSDictionary, hence observing exception
由于大多数答案都正确指出您将无法识别的选择器objectForKey:传递给NSString实例而不是NSDictionary，因此观察异常
-[__NSCFConstantString objectForKey:]:
Check NSUserDefaultsto see whether citiesreturns a dictionary or something else. You can do this by two ways
检查NSUserDefaults是否cities返回字典或其他内容。你可以通过两种方式做到这一点
I. NSLogall data in NSUserDefaults
一、NSLog所有数据在NSUserDefaults
NSLog(@"%@", [[NSUserDefaults standardUserDefaults] dictionaryRepresentation]);
II. Check the plist file which store the NSUserDefaultsfrom the Application folder. Check this answerfor more details.
二、检查存储NSUserDefaults来自 Application 文件夹的 plist 文件。检查此答案以获取更多详细信息。
Hope that helps.
希望有帮助。
