关于数组在遍历过程中修改问题

问题描述：当我们需要通过遍历数组过滤的时候，一般会考虑以下写法，这种写法 会引起crash

*** Collection <__NSArrayM: 0x7fddedfca720> was mutated while being enumerated.

 1 NSMutableArray *mutableArray = [[NSMutableArray alloc] initWithObjects:@"1",@"1",@"2",@"1",@"1",@"1",@"1",@"1",@"1",@"1", nil];
 2
 3     for (NSString *numStr in mutableArray) {
 4
 5         if ([numStr isEqualToString:@"2"]) {
 6
 7             [mutableArray removeObject:numStr];
 8
 9         }
10
11     }

问题解决：可以使用 方法

- (void)enumerateObjectsUsingBlock:(void (^)(id obj, NSUInteger idx, BOOL *stop))block NS_AVAILABLE(10_6, 4_0);

来避免这个crash

[mutableArray enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {

        if ([obj isEqualToString:@"2"]) {

            [mutableArray removeObject:obj];

        }

    }];

还可以拷贝一份数组来操作如：

1 NSMutableArray *mutableArray = [[NSMutableArray alloc] initWithObjects:@"1",@"1",@"2",@"1",@"1",@"1",@"1",@"1",@"1",@"1", nil];
2     NSArray *array = [NSArray arrayWithArray:mutableArray];
3     for (NSString *numStr in array) {
4         if ([numStr isEqualToString:@"2"]) {
5             [mutableArray removeObject:mutableArray];
6         }
7     }