Core Data浅谈系列之六 ： 验证用户输入

在做Web开发时，需要谨记的一条原则是“绝不要相信用户的任何输入”（参见《​​Essential PHP Security​​》）。

与网页上的表单提交类似，做客户端开发时也应该考虑用户输入，比如可以为UITextField设置代理处理用户实时输入的内容，也可以读取完用户输入再做检查，或者是NSManagedObject的 ​​验证功能​​。

Player的实现里提供验证函数： 

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1. #define PLAYER_ERROR_DOMAIN @"PLAYER_ERROR_DOMAIN"
2. 
3. enum _playerErrorCode {
4. PLAYER_INVALID_AGE_CODE = 0,
5. PLAYER_INVALID_NAME_CODE,
6. PLAYER_INVALID_CODE
7. };
8. typedef enum _playerErrorCode PlayerErrorCode;

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1. @implementation Player
2. 
3. @dynamic age;
4. @dynamic name;
5. @dynamic team;
6. 
7. - (BOOL)validateName:(id *)ioValue error:(NSError **)outError
8. {
9. NSString *playerName = *ioValue;
10. playerName = [playerName stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
11. if (!playerName || [playerName length] == 0) {
12. if (outError) {
13. "Player's name should not be empty.";
14. NSDictionary *userInfoDict = @{ NSLocalizedDescriptionKey : errorStr };
15. NSError *error = [[NSError alloc] initWithDomain:PLAYER_ERROR_DOMAIN
16. code:PLAYER_INVALID_NAME_CODE
17. userInfo:userInfoDict];
18. *outError = error;
19. }
20. return NO;
21. }
22. 
23. return YES;
24. }
25. 
26. @end

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1. 2013-01-17 22:36:42.393 cdNBA[673:c07] Error Error Domain=PLAYER_ERROR_DOMAIN Code=1 "Player's name should not be empty." UserInfo=0x827e380 {NSLocalizedDescription=Player's name should not be empty.}, Player's name should not be empty.

当然，我们绝对不会希望异常发生在这个位置，让程序直接挂掉 —— 这里只是一个Demo。

因为只有在保存context时才会调用验证函数，为了不让程序挂在这里，我们可以提前进行验证： 

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1. NSString *name = self.nameTextField.text;
2. NSError *error = NULL;
3. [playerObject validateValue:&name forKey:@"name" error:&error];
4. if (error) {
5. "%@\n", [error localizedDescription]);
6. }

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1. - (BOOL)validateForInsert:(NSError **)outError
2. {
3. BOOL valid = [super validateForInsert:outError];
4. 
5. NSString *playerName = self.name;
6. if (!playerName || [playerName length] == 0) {
7. if (outError) {
8. "Player's name should not be empty.";
9. NSDictionary *userInfoDict = @{ NSLocalizedDescriptionKey : errorStr };
10. NSError *error = [[NSError alloc] initWithDomain:PLAYER_ERROR_DOMAIN
11. code:PLAYER_INVALID_NAME_CODE
12. userInfo:userInfoDict];
13. *outError = [self errorFromOriginalError:error error:nil];
14. }
15. valid = NO;
16. }
17. 
18. NSInteger playerAge = [self.age integerValue];
19. if (!self.age || (playerAge < 16 || playerAge > 50)) {
20. if (outError) {
21. "Player's age should be in [16, 50].";
22. NSDictionary *userInfoDict = @{ NSLocalizedDescriptionKey : errorStr };
23. NSError *error = [[NSError alloc] initWithDomain:PLAYER_ERROR_DOMAIN
24. code:PLAYER_INVALID_AGE_CODE
25. userInfo:userInfoDict];
26. *outError = [self errorFromOriginalError:*outError error:error];
27. }
28. valid = NO;
29. }
30. 
31. return valid;
32. }
33. 
34. // Modified from https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CoreData/Articles/cdValidation.html
35. //
36. - (NSError *)errorFromOriginalError:(NSError *)originalError error:(NSError *)secondError
37. {
38. NSMutableDictionary *userInfo = [NSMutableDictionarydictionary];
39. 
40. NSMutableArray *errors = [NSMutableArrayarray];
41. if (secondError) {
42. [errors addObject:secondError];
43. }
44. 
45. if ([originalError code] == NSValidationMultipleErrorsError) {
46. [userInfo addEntriesFromDictionary:[originalError userInfo]];
47. [errors addObjectsFromArray:[userInfo objectForKey:NSDetailedErrorsKey]];
48. else {
49. [errors addObject:originalError];
50. }
51. 
52. [userInfo setObject:errors forKey:NSDetailedErrorsKey];
53. 
54. return [NSErrorerrorWithDomain:NSCocoaErrorDomain
55. code:NSValidationMultipleErrorsError
56. userInfo:userInfo];
57. }

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1. error = "Invalid username or password.";
2. error .= "Invalid token.";

NSManagedObject提供了三个函数用户在插入、修改、删除之前进行验证，分别是上面的validateForInsert，以及validateForUpdate和validateForDelete。

这次如果name和age都为空，则会输出如下错误信息： 

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1. 2013-01-17 23:42:03.979 cdNBA[1064:c07] Error Error Domain=NSCocoaErrorDomain Code=1560 "The operation couldn’t be completed. (Cocoa error 1560.)" UserInfo=0x111394b0 {NSDetailedErrors=(
2. "Error Domain=PLAYER_ERROR_DOMAIN Code=0 \"Player's age should be in [16, 50].\" UserInfo=0x1112fbf0 {NSLocalizedDescription=Player's age should be in [16, 50].}",
3. "Error Domain=PLAYER_ERROR_DOMAIN Code=1 \"Player's name should not be empty.\" UserInfo=0x11139430 {NSLocalizedDescription=Player's name should not be empty.}"
4. )}, The operation couldn’t be completed. (Cocoa error 1560.)

上面只是简单地对name和age进行是否为空的判定，实际操作还需要判断其它条件。比如还可以判断该球员是否已经存在，或者是之前提到的球队同名问题。

假设我们输入了合法的数据，创建了一名球员的信息，结果返回到上一级视图发现没有得到展现。对于这种情况，我们可以先很黄很暴力地在viewWillAppear里面重新reload下table，或者通过 ​​观察者模式​​监听相应的消息进行刷新。这里即将讨论的方法是使用NSFetchedResultsController这个类。