iPhone：变量范围问题

Question

我已经使用这段代码从plist中加载数据。

-(void)loadOrCreateData { 
    NSLog(@"Start loadOrCreateData"); 
    NSString *filePath = [self dataFilePath]; 
    if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) 
    { 
     NSLog(@"File Exists.. Loading from plist File"); 
     NSArray *array = [[NSArray alloc] initWithContentsOfFile:filePath]; 
     font = [array objectAtIndex:0]; 
     background = (NSString *)[array objectAtIndex:1]; 
     animation = [array objectAtIndex:5]; 
     [array release]; 
     NSLog(@"Loading Done!"); 
    } 
    else 
    { 
     NSLog(@"File does not exist.. Creating new plist File"); 
     font = @"Georgia-BoldItalic"; 
     background = @"monalisa.jpeg"; 
     animation = @"103"; 
     [self saveData]; 
    } 

    NSLog(@"Finish loadOrCreateData"); 
} 

- (NSString *)dataFilePath { 
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); 
    NSString *documentsDirectory = [paths objectAtIndex:0]; 
    return [documentsDirectory stringByAppendingPathComponent:@"data.plist"]; 
} 

- (void)saveData { 
    NSMutableArray *array = [[NSMutableArray alloc] init]; 
    [array addObject:font]; 
    [array addObject:background]; 
    [array addObject:animation]; 
    [array writeToFile:[self dataFilePath] atomically:YES]; 
    [array release]; 
} 

当没有plist文件获取数据时，第一次加载的时候一切正常。但在第二次加载时，当我尝试使用loadOrCreate方法之外的加载数据时，应用程序崩溃。由于某些原因，在loadOrCreate方法之外访问时，字体，背景和动画中的数据不可用。变量 - 字体，背景和动画在.h文件中声明为NSStrings，因此应该是全局可用的吗？你能告诉我这是什么原因吗？

Answer 1

您必须保留该对象。

font = [[array objectAtIndex:0] retain]; 
    background = (NSString *)[[array objectAtIndex:1] retain]; 
    animation = [[array objectAtIndex:5] retain]; 
... 
    font = [@"Georgia-BoldItalic" retain]; 
    background = [@"monalisa.jpeg" retain]; 
    animation = [@"103" retain]; 

注意：如果您要加载数据多次，那么不要忘记在设置它们之前释放值。

编辑：

-(void)loadOrCreateData { 
    [font release]; 
    [background release]; 
    [animation release]; 

    NSLog(@"Start loadOrCreateData"); 
    NSString *filePath = [self dataFilePath]; 
    if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) 
    { 
     NSLog(@"File Exists.. Loading from plist File"); 
     NSArray *array = [[NSArray alloc] initWithContentsOfFile:filePath]; 
     font = [[array objectAtIndex:0] retain]; 
     background = (NSString *)[[array objectAtIndex:1] retain]; 
     animation = [[array objectAtIndex:5] retain]; 
     [array release]; 
     NSLog(@"Loading Done!"); 
    } 
    else 
    { 
     NSLog(@"File does not exist.. Creating new plist File"); 
     font = [@"Georgia-BoldItalic" retain]; 
     background = [@"monalisa.jpeg" retain]; 
     animation = [@"103" retain]; 
     [self saveData]; 
    } 

    NSLog(@"Finish loadOrCreateData"); 
}