iphone开发中的数据存储：Property lists

定义两个方法：

- (NSString *)dataFilePath;获取返回数据文件的完整路径名

- (void)applicationWillResignActive:(NSNotification *)notification;保存数据，参数notification的作用是在对象之间传递通知，保持通信。

#define kFilename        @"data.plist"


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

 

- (void)applicationWillResignActive:(NSNotification *)notification {
    NSMutableArray *array = [[NSMutableArray alloc] init];
    [array addObject:field1.text];
    [array addObject:field2.text];
    [array addObject:field3.text];
    [array addObject:field4.text];
    [array writeToFile:[self dataFilePath] atomically:YES];
}

（例子程序为保存四个textField的字符）

之后在viewDidLoad中添加代码：

- (void)viewDidLoad
{
    [super viewDidLoad];

    NSString *filePath = [self dataFilePath];
    if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) {
        NSArray *array = [[NSArray alloc] initWithContentsOfFile:filePath];
        field1.text = [array objectAtIndex:0];
        field2.text = [array objectAtIndex:1];
        field3.text = [array objectAtIndex:2];
        field4.text = [array objectAtIndex:3];
    }
    
    UIApplication *app = [UIApplication sharedApplication];
    [[NSNotificationCenter defaultCenter] addObserver:self
        selector:@selector(applicationWillResignActive:)
        name:UIApplicationWillResignActiveNotification
        object:app];
}