17章：NSArray

NSArray

NSArray实例可以保存一组指向其他对象的指针。

17.1创建数组

        NSDate *now = [NSDate date];
        NSDate *tomorrow = [now dateByAddingTimeInterval:24.0*60.0*60.0];
        NSDate *yesterday = [now dateByAddingTimeInterval:-24.0*60.0*60.0];
        NSArray *dateList = @[now,tomorrow,yesterday];

NSArry实例一旦被创建后，就无法添加或删除数组里的指针，也无法改变数组的指针顺序。

17.2存取数组

        NSDate *now = [NSDate date];
        NSDate *tomorrow = [now dateByAddingTimeInterval:24.0*60.0*60.0];
        NSDate *yesterday = [now dateByAddingTimeInterval:-24.0*60.0*60.0];
        NSArray *dateList = @[now,tomorrow,yesterday];

        NSLog(@"is %@",dateList[0]);
        NSLog(@"there are %lu dates",[dateList count]);

遍历数组

        NSDate *now = [NSDate date];
        NSDate *tomorrow = [now dateByAddingTimeInterval:24.0*60.0*60.0];
        NSDate *yesterday = [now dateByAddingTimeInterval:-24.0*60.0*60.0];
        NSArray *dateList = @[now,tomorrow,yesterday];
        for(int i=0;i<dateList.count;i++){

        }
        for(NSDate *d in dateList){
            NSLog(@"Here is a date : %@",d);
        }

NSMutableArray

可以添加删除或对指针重新进行排序。

        NSDate *now = [NSDate date];
        NSDate *tomorrow = [now dateByAddingTimeInterval:24.0*60.0*60.0];
        NSDate *yesterday = [now dateByAddingTimeInterval:-24.0*60.0*60.0];
        NSMutableArray *dateList = [NSMutableArray array];
        [dateList addObject:now];
        [dateList addObject:tomorrow];
        [dateList insertObject:yesterday atIndex:0];
        for(NSDate *d in dateList){

        }
        [dateList removeObjectAtIndex:0];

        NSArray *dateList = [NSArray arrayWithObjects:now,tommorow,yesterday,nil];
        [dateList objectAtIndex:0];
        [dateList count];
        NSArray *ne = @[now,tomorrow,yesterday];
        NSDate *firstDate = dateList[0];