iOS數據持久化（1、NSUserDefaults）

　　NSUserDefaults適合存儲輕量級的本地數據，好比要保存一個登錄界面的數據，用戶名、密碼之類的，我的以爲使用NSUserDefaults是首選(須要加密的登陸信息請略過)。下次再登錄的時候就能夠直接從NSUserDefaults裏面讀取上次登錄的信息咯。

由於若是使用本身創建的plist文件什麼的，還得本身顯示建立文件，讀取文件，很麻煩，而是用NSUserDefaults則不用管這些東西，就像讀字符串同樣，直接讀取就能夠了。

　　NSUserDefaults支持的數據格式有：NSNumber（Integer、Float、Double），NSString，NSDate，NSArray，NSDictionary，BOOL類型。很實用吧

NSUserDefaults很方便，讀取也很容易。下面給出一個示例看看如何使用：

//保存數據到NSUserDefaults
-(void)saveNSUserDefaults
{
    NSString *myString = @"enuola";
    int myInteger = 100;
    float myFloat = 50.0f;
    double myDouble = 20.0;
    NSDate *myDate = [NSDate date];
    NSArray *myArray = [NSArray arrayWithObjects:@"hello", @"world", nil];
    NSDictionary *myDictionary = [NSDictionary dictionaryWithObjects:[NSArray arrayWithObjects:@"enuo", @"20", nil] forKeys:[NSArray    arrayWithObjects:@"name", @"age", nil]];
    
    //將上述數據所有存儲到NSUserDefaults中
    NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
    //存儲時，除NSNumber類型使用對應的類型意外，其餘的都是使用setObject:forKey:
    [userDefaults setInteger:myInteger forKey:@"myInteger"];
    [userDefaults setFloat:myFloat forKey:@"myFloat"];
    [userDefaults setDouble:myDouble forKey:@"myDouble"];
    
    [userDefaults setObject:myString forKey:@"myString"];
    [userDefaults setObject:myDate forKey:@"myDate"];
    [userDefaults setObject:myArray forKey:@"myArray"];
    [userDefaults setObject:myDictionary forKey:@"myDictionary"];
    
    //這裏建議同步存儲到磁盤中，可是不是必須的
    [userDefaults synchronize];
    
}

//從NSUserDefaults中讀取數據
-(void)readNSUserDefaults
{
    NSUserDefaults *userDefaultes = [NSUserDefaults standardUserDefaults];
    
    //讀取數據到各個label中
    //讀取整型int類型的數據
    NSInteger myInteger = [userDefaultes integerForKey:@"myInteger"];
    NSString *myIntegerStr = [NSString stringWithFormat:@"%ld",(long)myInteger];
    NSLog(@"%@",myIntegerStr);
    
    //讀取浮點型float類型的數據
    float myFloat = [userDefaultes floatForKey:@"myFloat"];
    NSString *myFloatStr = [NSString stringWithFormat:@"%f",myFloat];
     NSLog(@"%@",myFloatStr);
    //讀取double類型的數據
    double myDouble = [userDefaultes doubleForKey:@"myDouble"];
    NSString *myDoubleStr = [NSString stringWithFormat:@"%f",myDouble];
    NSLog(@"%@",myDoubleStr);
    
    //讀取NSString類型的數據
    NSString *myString = [userDefaultes stringForKey:@"myString"];
    NSString *myStringStr = myString;
    NSLog(@"%@",myStringStr);
    
    //讀取NSDate日期類型的數據
    NSDate *myDate = [userDefaultes valueForKey:@"myDate"];
    NSDateFormatter *df = [[NSDateFormatter alloc] init];
    [df setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
    NSString *myDateStr = [NSString stringWithFormat:@"%@",[df stringFromDate:myDate]];
    NSLog(@"%@",myDateStr);
    
    //讀取數組NSArray類型的數據
    NSArray *myArray = [userDefaultes arrayForKey:@"myArray"];
    NSString *myArrayString = [[NSString alloc] init];
    for(NSString *str in myArray)
    {
        NSLog(@"str= %@",str);
        myArrayString = [NSString stringWithFormat:@"%@  %@", myArrayString, str];
        [myArrayString stringByAppendingString:str];
        //        [myArrayString stringByAppendingFormat:@"%@",str];
        NSLog(@"myArrayString=%@",myArrayString);
    }
    NSString *myArrayStr = myArrayString;
    NSLog(@"%@",myArrayStr);
    
    //讀取字典類型NSDictionary類型的數據
    NSDictionary *myDictionary = [userDefaultes dictionaryForKey:@"myDictionary"];
    NSString *myDicString = [NSString stringWithFormat:@"name:%@, age:%ld",[myDictionary valueForKey:@"name"], (long)[[myDictionary valueForKey:@"age"] integerValue]];
    NSString *myDictTionary = myDicString;
    NSLog(@"%@",myDictTionary);
}