Question

我有一个字符串数组，如下所示

newlymadeArray(
"03/05/2013",
"09/22/2013",
"03/02/2013",
"03/02/2013",
"08/22/2013",
"11/02/2013",
"07/08/2013",
"08/31/2013",
"05/13/2013",
"07/11/2013",
"10/07/2013",
"02/20/2013"

）

目前的甲酸盐是MM / dd / yyyy

我想将其更改为dd / MM / yyyy

我正在使用以下代码

  NSLog(@"_newlymadeArray%@",_newlymadeArray);
//logic for changing date formate
for( int i=0; i<_newlymadeArray.count; i++){
    NSDateFormatter *dateFormatter1 = [[NSDateFormatter alloc] init];
    [dateFormatter1 setDateFormat:@"MM/dd/yyyy"];
    NSDateFormatter *dateFormatter2 = [[NSDateFormatter alloc] init];
    [dateFormatter2 setDateFormat:@"dd/MM/yyyy"];

    NSDate *old = [dateFormatter1 dateFromString:[_newlymadeArray objectAtIndex:i]];
    NSLog(@"old %@",old);

    NSString *old1 =[dateFormatter1 stringFromDate:old];

    NSDate *new = [dateFormatter2 dateFromString:old1];
    NSLog(@"new %@",new);

    NSString *string = [dateFormatter2 stringFromDate:new];
    NSLog(@"string %@",string);

    [_convertedBdates addObject:string];

        }

      NSLog(@"_convertedBdates%@",_convertedBdates);

这就是我得到的输出

  old 2013-03-04 18:30:00 +0000
  new 2013-05-02 18:30:00 +0000
  string 03/05/2013
  old 2013-09-21 18:30:00 +0000
  new (null)
 string (null)
 ] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason:     '*** -[__NSArrayM insertObject:atIndex:]: object cannot be nil'
 *** First throw call stack:

我的问题是为什么旧的打印2013-03-04而不是05/03/2013 在第一次循环结束时它被打印03/05/2013而不是05/03/2013 当循环第二次运行时，它在new中获取null值，这就是为什么在数组程序中添加空值会崩溃的原因

请告诉我，我做错了什么？

Answer 1

这永远不会适合：

NSString *old1 =[dateFormatter1 stringFromDate:old];
NSDate *new = [dateFormatter2 dateFromString:old1];

您说，“使用一个格式化程序格式化日期...然后使用另一个格式化程序解析它。”

您已经解析了旧格式的值。您现在需要在新的格式化程序中格式化。

我不是Objective-C开发人员，但我怀疑你只是想要：

NSDate *date = [dateFormatter1 dateFromString:[_newlymadeArray objectAtIndex:i]];
NSString *string = [dateFormatter2 stringFromDate:date];
[_convertedBdates addObject:string];

请注意，只涉及一个日期，但有两个字符串（原始格式和新格式）。

另请注意，无需在循环的每次迭代中创建一对新的格式化程序。在循环之前创建它们并重用它们：

NSDateFormatter *oldFormatter = [[NSDateFormatter alloc] init]; [oldFormatter setDateFormat:@"MM/dd/yyyy"]; NSDateFormatter *newFormatter = [[NSDateFormatter alloc] init]; [newFormatter setDateFormat:@"dd/MM/yyyy"]; for (int i = 0; i < _newlymadeArray.count; i++) { NSDate *date = [oldFormatter dateFromString:[_newlymadeArray objectAtIndex:i]]; NSString *string = [newFormatter stringFromDate:date]; [_convertedBdates addObject:string]; }

（当然，还想要检查循环中date是否为空，以处理错误数据。）

Answer 2

试试这个：

NSDateFormatter *dateFormatter1 = [[NSDateFormatter alloc] init];
[dateFormatter1 setDateFormat:@"MM/dd/yyyy"];
NSDateFormatter *dateFormatter2 = [[NSDateFormatter alloc] init];
[dateFormatter2 setDateFormat:@"dd/MM/yyyy"];
for( int i=0; i<_newlymadeArray.count; i++){

    NSDate *old = [dateFormatter1 dateFromString:[_newlymadeArray objectAtIndex:i]];
    NSLog(@"old %@",old);

    if (old) {
        NSString *newDateString = [dateFormatter2 stringFromDate:old];
        NSLog(@"new %@",newDateString);
        [_convertedBdates addObject:newDateString];
    }
}
[dateFormatter1 release];
[dateFormatter2 release];

Answer 3

NSDateFormatter *fromDateFormatter = [[NSDateFormatter alloc] init];
[fromDateFormatter setDateFormat:@"MM/dd/yyyy"];

NSDateFormatter *toDateFormatter = [[NSDateFormatter alloc] init];
[toDateFormatter setDateFormat:@"dd/MM/yyyy"];

for (NSString *dateString in newlyMadeArray)
{
    NSDate *date = [fromDateFormatter dateFromString:dateString];
    NSString *newDateString = [toDateFormatter stringFromDate:date];
    [_convertedBdates addObject:newDateString];
}

Answer 4

首先你应该将字符串“MM / dd / yyyy”转换为“dd / MM / yyyy”。

for( int i=0; i<_newlymadeArray.count; i++){
    NSDateFormatter *dateFormatter1 = [[NSDateFormatter alloc] init];
    [dateFormatter1 setDateFormat:@"MM/dd/yyyy"];
    NSDateFormatter *dateFormatter2 = [[NSDateFormatter alloc] init];
    [dateFormatter2 setDateFormat:@"dd/MM/yyyy"];

    NSDate *old = [dateFormatter1 dateFromString:[_newlymadeArray objectAtIndex:i]];
    NSLog(@"old %@",old);



NSArray *arr = [[_newlymadeArray objectAtIndex:i] componentsSeparatedByString:@"/"];
    NSString *old1 = [NSString stringWithFormat:@"%@/%@/%@",[arr objectAtIndex:1],[arr objectAtIndex:0],[arr objectAtIndex:2]];
    NSDate *new = [dateFormatter2 dateFromString:old1];
    NSLog(@"new %@",new);

    NSString *string = [dateFormatter2 stringFromDate:new];
    NSLog(@"string %@",string);

    [_convertedBdates addObject:string];

        }

更改日期格式的问题

4 个答案: