iOS强制类型转换陷阱

1、C风格的类型转换

object-c中，我们经常使用C语言风格的强制类型转换：(Type)var

//Sample
    UILabel *lb = (UILabel *)[self.view viewWithTag:100];
    NSArray *arr = [NSArray array];
    NSMutableArray *mutableArr = (NSMutableArray *)arr;

一般情况下，在转换之后我们可以安全的得到想要的类型。

2、陷阱

通过以上方式将NSArray转变成NSMutableArray只是消除了编译器警告，并没有真正转换成可变数组。

NSArray *citys = [NSArray arrayWithObjects:@"深圳",@"北京",@"上海",@"广州", nil];
    NSMutableArray *mutableArr = (NSMutableArray *)citys;
    [mutableArr removeObjectAtIndex:0];

运行崩溃：

2014-10-17 15:52:18.132 Pro4Test[5240:60b] *** Terminating app due to uncaught exception "NSInvalidArgumentException", reason: "-[__NSArrayI removeObjectAtIndex:]: unrecognized selector sent to instance 0x1468b8e0"

__NSArrayI是指NSArray,__NSArrayM才是NSMutableArray

3、可变类型转换

NSArray *arr = [NSArray arrayWithObjects:@"深圳",@"北京",@"上海",@"广州", nil];
    NSDictionary *dic = [NSDictionary dictionaryWithObjectsAndKeys:@"深圳",@"city", nil];
    //可变数组
    NSMutableArray *mutableArr = [NSMutableArray arrayWithArray:arr];
    //or NSMutableArray *mutalbeArr = [[[NSMutableArray alloc] initWithArray:citys] autorelease];
    //可变字典
    NSMutableDictionary *mutableDic = [NSMutableDictionary dictionaryWithDictionary:dic];
    //or NSMutableDictionary *mutableDic = [[[NSMutableDictionary alloc] initWithDictionary:dic] autorelease];