Question

.h

@property (nonatomic, retain) NSArray *m_plistData;

.m

@synthesize m_plistData;
- (void)viewDidLoad
{   
    NSArray *array = [[NSArray alloc]initWithObjects:@"0",@"1",@"2",@"3",@"4",@"5",@"6",@"7",@"8",@"9",@"10",@"11",@"12",@"13",@"14", nil];    
    m_plistData = array;
    NSArray *nn = m_plistData;    
    [super viewDidLoad];    
}

I use breakpoint and found array is normal,but m_plistData has no values,shows “out of scope”,I can’t understand why nn can get normal values

Answer 1

array is a local reference variable. It just lasts until viewDidLoad method. Now,

m_plistData = array;

The above statement doesn’t make a deep copy. It is just a shallow copy.

- (void)viewDidLoad
{   
    NSArray *array = [[NSArray alloc]initWithObjects:@"0",@"1",@"2",@"3",@"4",@"5",@"6",@"7",@"8",@"9",@"10",@"11",@"12",@"13",@"14", nil];    
    m_plistData = array;
    NSArray *nn = m_plistData;    
    [super viewDidLoad];    
} // Both the array, nn references cease to exist after this point.
  // So having references to it leads to run-time exception if used else where.

If your objective is have elements in m_plistData, directly do –

m_plistData = [[NSArray alloc]initWithObjects:@"0",@"1",@"2",@"3",@"4",@"5",@"6",@"7",@"8",@"9",@"10",@"11",@"12",@"13",@"14", nil];