比较日期

Question

i am trying to compare the date but its not comparing the date like 31-dec-2011 with 1-01-2012. i was trying to remove values at 31-dec-2011 and any other values previous then 1-01-2012. here i am doing this: i want to show the values at today's date and on upcoming dates.

-(void)showcurrentdate
{
    NSDate *objdate=[NSDate date];
NSDateFormatter *dateformatter = [[NSDateFormatter alloc] init];
[dateformatter setDateFormat:@"dd-MM-YYYY"];

NSDate *str1= (NSDate *)[dateformatter stringFromDate:objdate];

NSLog(@"configuregameArray......%d",[configuregameArray count]);

if([configuregameArray count]>=1)
{    
  NSMutableArray* indexarray= [[NSMutableArray alloc]init];  
  for(int k =0; k<[configuregameArray count]; k++)
 {

    NSDate *datefromarray = (NSDate *)[[configuregameArray objectAtIndex:k] objectForKey:@"gd"];  

     NSComparisonResult result = [datefromarray compare:str1];

     switch (result)
     {               

         case NSOrderedAscending:

             NSLog(@"%@ is greater from %@", str1 ,datefromarray);
             indexNumber = [NSString stringWithFormat:@"%d",k];
             [indexarray addObject:indexNumber];
             NSLog(@"indexarray......%@",indexarray);
             break;


         default: 
             NSLog(@"going fine");   
                            break;
     }

 }


    NSMutableIndexSet *discardedItems = [NSMutableIndexSet indexSet];
    for(int i=0; i<[indexarray count]; i++)
    {
       NSInteger removeindex = [[indexarray objectAtIndex:i]intValue];        
       [discardedItems addIndex:removeindex];

     }

    [configuregameArray removeObjectsAtIndexes:discardedItems];
}
NSLog(@"configuregameArray......%@",configuregameArray);

}

Answer 1

Given that you have your dates stored as strings in another array and that you want to end up with an array of strings, filtering out only the dates that occur after a certain date would take these steps:

• Get the date to filter with
• Loop over all strings
  • Use a date formatter to convert the string to a date object.
  • Compare the converted date to the filter date
    • Store the index of the date string if the converted date occurs after the filter date
• Create a new array of strings with the indexes you stored while looping all strings.

Obviously it would be better to store dates in the array. This make all date calculations much easier. Then you could filter the array with a one line NSPredicate instead of many lines of code. It is generally a bad design to store objects as strings. A much better practice is to store the objects as objects and convert them to strings when presenting them in a user interface. This was you can change how the objects are formatted without having to change how they are stored, converted, and used. It is a separation of concerns where the interface who is concerned about showing dates as strings converts dates to strings while the model who is concerned about dates uses dates and doesn't care about strings at all.

Anyhow, code for the above steps to filter the date strings in your question would look something like below. If you want to filter using todays date you can use [NSDate date]; to get todays date as a date and not a string.

    // Create some sample date strings 
    NSArray *dateStrings = [NSArray arrayWithObjects:@"01-01-2012", @"03-01-2012", @"01-03-2012", @"10-08-2011", @"06-02-2002", @"20-04-1999", @"01-01-2012", @"31-12-2011", @"07-03-2014", @"18-09-3456", @"27-07-1924", nil];

    // The same kind date format as the question
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    dateFormatter.dateFormat = @"dd-MM-YYYY";

    // The date that other dates are filtered using
    NSDate *filterDate = [dateFormatter dateFromString:@"01-01-2012"];

    ///////////// OUTPUT /////////////
    NSLog(@"BEFORE: %@", dateStrings);
    //////////////////////////////////

    // Get the indexes of all dates after the filterDate.
    NSIndexSet *newerDateIndexes = [dateStrings indexesOfObjectsPassingTest:^BOOL(id obj, NSUInteger idx, BOOL *stop) {
        NSString *dateString = (NSString *)obj; // The string stored in the array
        NSDate *date = [dateFormatter dateFromString:dateString]; // Use the dateFormatter to get a date from the array

        // Add this index to the index set if the date occurs after the filterDate.
        return ([date compare:filterDate] != NSOrderedAscending);
    }];

    // A new array with only the dates after the filterDate
    NSArray *filteredDateString = [dateStrings objectsAtIndexes:newerDateIndexes];

    ///////////// OUTPUT ///////////////////
    NSLog(@"AFTER: %@", filteredDateString);
    ////////////////////////////////////////

Answer 2

You cannot simply cast one class to another except of they're related (casting to super/subclass).

So you should do it like this:

• Either store NSDate instances in your array. Then all you have to do is compare the dates with your objdate . That would be the best solution.
• Or turn every string into a date (using [dateformatter dateFromString:] ) and compare the resulting date with your objdate .
• You shouldn't compare the string representations as you'll get "strange" results if you don't us a reverse format like YYYY-MM-dd .