ios NSDictionary 具有空值
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NSDictionary having null value
提问by Kalyan Urimi
I have a problem when Extracting data from a Dictionary object. Count of the Dictionary is displaying as 1, but the one value it is displaying is null. I want to display a AlertView when there is no data in the Dictionary object. I thought of displaying the AlertView when the count is '0', but it returning '1'.
从 Dictionary 对象中提取数据时遇到问题。字典的计数显示为 1，但它显示的一个值为空。当 Dictionary 对象中没有数据时，我想显示 AlertView。我想在计数为“0”时显示 AlertView，但它返回“1”。
I am extracting this dictionary object from a WebService using JSON.
我正在使用 JSON 从 WebService 中提取这个字典对象。
{
"My Data" = null;
}
Used this code for getting the "My Data" value into the Dictionary variable Datas.
使用此代码将“我的数据”值放入字典变量数据中。
Datas = (NSDictionary *) [details objectForKey:@"My Data"];
if ([Datas count] == 0) {
//code for showing AlertView....
}
Please help me to display a UIAlertView when the Dictionary value having null....
请帮助我在 Dictionary 值为 null 时显示 UIAlertView ....
回答by dasblinkenlight
NSDictionaryand other collections cannot contain nilvalues. When NSDictionarymust store a null, a special value [NSNull null]is stored.
NSDictionary和其他集合不能包含nil值。当NSDictionary必须存储 a 时null，存储一个特殊值[NSNull null]。
Compare the value at @"My Data"to [NSNull null]to determine if the corresponding value is nullor not.
在比较值@"My Data"来[NSNull null]确定对应的值null或不是。
// Since [NSNull null] is a singleton, you can use == instead of isEqual
if ([details objectForKey:@"My Data"] == [NSNull null]) {
// Display the alert
}
回答by Carl Veazey
Usually null values in JSON get parsed to NSNull. So this condition should check for that as well as nil: if((details[@"My Data"] == nil) || (details[@"My Data"] == [NSNull null]))
通常 JSON 中的空值被解析为NSNull. 所以这个条件应该检查那个以及零：if((details[@"My Data"] == nil) || (details[@"My Data"] == [NSNull null]))
回答by Paras Joshi
if ([[details objectForKey:@"My Data"] isEqual:[NSNull null]] || [[details objectForKey:@"My Data"] isEqualToString:@""]) {
UIAlertView *altTemp = [UIAlertView alloc]initWithTitle:@"Value Null" message:@"Your Message" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
[altTemp show];
[altTemp release];
}
