数据持久化基础知识——属性列表

 1 //插入4个文本框
 2 @property (strong, nonatomic) IBOutletCollection(UITextField) NSArray * lineFields;
 3 
 4 
 5 //获取路径，检查数据文件是否存在，存在则显示在文本框中。
 6 - (void)viewDidLoad {
 7     [super viewDidLoad];
 8     NSString * filePath = [self dataFilePath];
 9     if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) {
10         NSArray * array = [[NSArray alloc] initWithContentsOfFile:filePath];
11         for (int i = 0; i < 4; i++) {
12             UITextField * theField = self.lineFields[i];
13             theField.text = array[i];
14         }
15     }
16 
17 //终止运行或者进入后台之前保存数据。
18     UIApplication * app = [UIApplication sharedApplication];
19     [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(applicationWillResignActive:) name:UIApplicationWillResignActiveNotification object:app];
20 }
21 
22 //获取文件路径，并返回。
23 - (NSString *)dataFilePath
24 {
25     NSArray * paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
26     NSString * documentsDirectory = [paths objectAtIndex:0];
27     return [documentsDirectory stringByAppendingPathComponent:@"data.plist"];
28 }
29 
30 //终止运行或者进入后台之前执行的方法。
31 - (void)applicationWillResignActive:(NSNotification *)notification
32 {
33     NSString * filePath = [self dataFilePath];
34     
35      //通过调用lineFields数组中每个文本框的text方法构建一个字符串数组，对数组调用valueForKey：方法，并传递@“text”作为参数，实现了迭代获取实例变量的text值。
36     NSArray * array = [self.lineFields valueForKey:@"text"];
37     [array writeToFile:filePath atomically:YES];
38 }