Question

嗨我有这样的功能

- (void)save{
        NSLog(@" %@ %@ %@ %@",AppAddressLine,AppCustomerName,AppPhoneNumber,AppPriceTier);

        paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        documentsDirectory = [paths objectAtIndex:0];
        path = [documentsDirectory stringByAppendingPathComponent:@"NewInAppCustomer.plist"];
        NSMutableArray *MainRoot=[[NSMutableArray alloc]initWithContentsOfFile:path];
        NSMutableDictionary *ContentDictionary=[[NSMutableDictionary alloc]init];
        [ContentDictionary setValue:AppCustomerName  forKey:@"CustomerName"];
        [ContentDictionary setValue:AppAddressLine forKey:@"CustomerAddress"];
        [ContentDictionary setValue:AppPhoneNumber forKey:@"CustomerPhoneNumber"];
        [ContentDictionary setValue:AppPriceTier forKey:@"CustomerPriceTier"];
        [MainRoot addObject:ContentDictionary];
        [MainRoot writeToFile:path atomically:YES];
        NSLog(@"%@",MainRoot);

}

用

打印时

NSLog(@" %@ %@ %@ %@",AppAddressLine,AppCustomerName,AppPhoneNumber,AppPriceTier);

显示正确的值，

但这一行

NSLog(@"%@",MainRoot);

显示nil作为其值。

有人可以向我解释一下吗？

Answer 1

这一行：

NSMutableArray *MainRoot=[[NSMutableArray alloc]initWithContentsOfFile:path];

将返回nil if：

无法打开文件或无法将文件内容解析为数组

所以你有一个不存在或无效的文件。

因此，您应该确保在此代码运行之前创建文件，或者更好的是，检查结果并在需要时创建一个新的空数组。

if (MainRoot == nil) MainRoot = [NSMutableArray array];

Answer 2

试试这个，如果文件不存在则创建该文件然后写入

- (void)save{
        NSLog(@" %@ %@ %@ %@",AppAddressLine,AppCustomerName,AppPhoneNumber,AppPriceTier);

        paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        documentsDirectory = [paths objectAtIndex:0];
        path = [documentsDirectory stringByAppendingPathComponent:@"NewInAppCustomer.plist"];
        NSMutableArray *mainRoot;
        NSFileManager *fileManager = [NSFileManager defaultManager];
        if (![fileManager fileExistsAtPath:path]) {

             [fileManager createDirectoryAtPath:path withIntermediateDirectories:NO attributes:nil error:&error];
             mainRoot = [[NSMutableArray alloc] init];
        } else {
             mainRoot = [[NSMutableArray alloc] initWithContentsOfFile:path];
        }
        ....
}

NSMutableArray显示（null）/ nil？

2 个答案: