NSMutableDictionary 的奇怪行为
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- (NSMutableDictionary *)getUsersFromServer
{
//here we're getting list of users from the server
NSMutableDictionary * users = [[[NSMutableDictionary alloc] init] autorelease];
userresults = [[NSMutableArray alloc] init];
//all this will be replaced with users taken from the server. it's needed just for testing
for (int i = 0;i < 19;i++)
{
int wins = i ; float f_wins = (float)wins;
int losses = i * 2 ; float f_losses = (float)losses;
int withdr = i * 3 ; float f_withdr = (float)withdr;
float win_per = f_wins / ((f_wins + f_losses + f_withdr) / 100.0);
[userresults setArray:[NSMutableArray arrayWithObjects:[NSNumber numberWithInt:wins],
[NSNumber numberWithInt:losses],
[NSNumber numberWithInt:withdr],
[NSNumber numberWithFloat:win_per],
nil]];
[users setObject:userresults forKey:[NSString stringWithFormat:@"user number %i",i]];
}
[userresults release];
return users;
}
每次循环迭代中的这段代码，我用数字填充数组并将其设置为 NSMutableDictionary 中的值。作为每个数组的键，提供格式化字符串，该字符串根据迭代计数器的数量是唯一的。所以...问题是 - 字典总是填充不同键的相同数组。字典中有 19 个数组，而且它们都是最后的！！！！这是上一次迭代的结果。而且每个人都有不同的钥匙！怎么可能发生？？？这是怎么回事？？？
Take a look at this piece of code
- (NSMutableDictionary *)getUsersFromServer
{
//here we're getting list of users from the server
NSMutableDictionary * users = [[[NSMutableDictionary alloc] init] autorelease];
userresults = [[NSMutableArray alloc] init];
//all this will be replaced with users taken from the server. it's needed just for testing
for (int i = 0;i < 19;i++)
{
int wins = i ; float f_wins = (float)wins;
int losses = i * 2 ; float f_losses = (float)losses;
int withdr = i * 3 ; float f_withdr = (float)withdr;
float win_per = f_wins / ((f_wins + f_losses + f_withdr) / 100.0);
[userresults setArray:[NSMutableArray arrayWithObjects:[NSNumber numberWithInt:wins],
[NSNumber numberWithInt:losses],
[NSNumber numberWithInt:withdr],
[NSNumber numberWithFloat:win_per],
nil]];
[users setObject:userresults forKey:[NSString stringWithFormat:@"user number %i",i]];
}
[userresults release];
return users;
}
in each loop iteration i fill array with numbers and set it as value into NSMutableDictionary. As a key for each array serves formatted string which is unique by number of iteration counter. So... the problem is - the dictionary is always filled with SAME arrays for DIFFERENT keys. There are 19 arrays in the dictionary and ALL THEY ARE LAST ONES!!!! That is from the last iteration. And each one has different key!!! How could it happen??? What's going on???
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userresults指向同一个对象，并且您正在使用setArray:方法修改同一个数组。在每次循环迭代中创建一个新数组：userresultspoints to the same object, and you're modifying that same array with thesetArray:method. Create a new array in each loop iteration instead:userresults 不必要地在循环外部声明。您可以在此处放弃可变数组，而只需在每次迭代时创建一个新的 NSArray。您的问题源于重用循环外部声明的数组并每次都放入新值。试试这个：
userresults is declared outside the loop unnecessarily. You can forego mutable arrays here and just create a new NSArray with each iteration. Your problem stems from reusing the array declared outside the loop and putting new values in each time. Try this: