Replace, move objects in NSMutableArray

问题

I Have an array which I have already set the capacity to 5. What I want to do is, when I add an object and the capacity exceeds 5 then it moves the whole array structure of objects by one. For example 1,2,3,4,5 (array). Then when 6 comes to be added It must replace 5 and delete one to result in 2,3,4,5,6 and so on.. So in other words it has to save only last 5 objects. BUT as in the actual coding it will save objects with coordinates in an array with capacity of 100+ so it has to be quick and efficient. I tried with int to see how it progresses:

      NSMutableArray *array = [[NSMutableArray alloc] initWithCapacity:5];

            int i;
            for (i = 0; i<=20;i++ ) {
                NSNumber *number = [NSNumber numberWithInt:i];
                if (i>=5) {
                [array insertObject:number atIndex:5];
                }else{
                [array addObject:number];
                }
                NSLog(@"array = %@, count = %i",array, array.count);
            }

but it stores all 20 in sorting like 1,2,3,4,20,19,18,17...6 any help would be appreciated! Thank you in advance..

回答1:

If index is already occupied, the objects at index and beyond are shifted by adding 1 to their indices to make room. so what you can use is replaceObjectAtIndex:withObject: this will replace the object. but if you want to remove the first object you do it your self. first check the length of the array. if greater than 5 remove the first element and shift all the objects to the the lower index. then add the new object.

if ([array count]>=5)
{
[array removeObjectAtIndex:index];

[array insertObject:new object atIndex :5];

回答2:

You can do this way:

Even you can put addTo:withValueLast: as a category:

-(NSMutableArray *)addTo:(NSMutableArray *)array withLastValue:(NSNumber *)number{
    if (array.count<5) {
        [array addObject:number];
    }
    else{
        [array removeObjectAtIndex:0];
        [array addObject:number];
    }
    return array; }

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    NSMutableArray *array = [[NSMutableArray alloc] initWithCapacity:5];

    for (int i=0; i<=20; i++) {
        NSNumber *number = [NSNumber numberWithInt:i];
        [self addTo:array withLastValue:number];
        NSLog(@"array = %@, count = %ld",array, array.count);
    } 
}

Using a Category:

.h file:

@interface NSMutableArray (Slide)
-(NSMutableArray *)slideWithValue:(NSNumber *)number;
@end

.m file:

#import "NSMutableArray+Slide.h"

@implementation NSMutableArray (Slide)

-(NSMutableArray *)slideWithValue:(NSNumber *)number{
    if (self.count<5) {
        [self addObject:number];
    }
    else{
        [self removeObjectAtIndex:0];
        [self addObject:number];
    }
    return self; 
} 
@end

Now your code goes as :

NSMutableArray *array = [[NSMutableArray alloc] initWithCapacity:5];
for (int i=0; i<=20; i++) {
    NSNumber *number = [NSNumber numberWithInt:i];
    [array slideWithValue:number];

    NSLog(@"array = %@, count = %ld",array, array.count);
}

回答3:

Create the method of adding value to array like this .It will remove the first object when it exceeds 5 an d add the last object .Problem solved

-(void)addObjectToArray:(id)lastObj
{
   [array addObject:lastObj];
    if ([array count]>5) {
        [array removeObjectAtIndex:0];
    }
}

happy Coding.

来源：https://stackoverflow.com/questions/15018637/replace-move-objects-in-nsmutablearray

标签

objective-c

xcode

arrays

for-loop

nsmutablearray