需要幫助在ViewControllers之間傳輸數據

Question

我想保持我的項目組織得更好，而不是將我的Appdelegate與我想從viewcontroller傳輸到viewcontroller的數據重載，我想創建一個模型類來幫助保持組織更有條理。但是，使用模型時，我很難在控制器之間傳輸數據。嘗試將此nsstring數據從ViewController1轉移到ViewController2時，您能否告訴我我的方式有錯誤？附：我做了這個例子，因爲我的真實項目有點混亂，所以我提前爲任何不一致道歉。在NSLog報告零以下結果

ViewController2.m 

ViewController1.m

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{ 
ViewController2 *viewController2 =[[ViewController2 alloc]init]; 
ViewControllerModel *vcm = [self.array objectAtIndex:indexPath.row]; 

NSLog(@"%@",vcm.string) // this will output a number 

[self.navigationController pushViewController:viewController2 animated:YES]; 
} 
// this delegate fetches an array of json data 
-(void)fetchedResults:(NSMutableArray*)arrayList{ 
self.array = arrayList; 
} 

ViewController2.m

- (void)viewDidLoad 
    { 
    ViewControllerModel *vcm = = [[ViewController alloc] init]; 
    [super viewDidLoad]; 
    NSLog(@"%@",vcm.string); // this will output null. 
    } 

ViewControllerModel .H ＃進口

@interface ViewControllerModel : NSObject 
    @property (nonatomic, strong) NSString *string; 

    @end 

ViewControllerModel.m

#import "ViewControllerModel.h" 

    @implementation ViewControllerModel 
    @synthesize string; 

    @end 

MyHandler.m

//this is where vcm.string in ViewController1.m will get all the numbers not sure if this is needed but just in case . 

    for (NSDictionary *dict in responseArray) 
    { 
    ViewControllerModel *vcm = [[ViewControllerModel alloc] init]; 

    vcm.string = ([dict valueForKey:@"string"] == [NSNull null]) ? @"" : [NSString stringWithFormat:@"%@",[dict valueForKey:@"string"]]; 

Answer 1

做以下修改：

ViewController1.m

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{ 
    ViewController2 *viewController2 =[[ViewController2 alloc]init]; 
    ViewControllerModel *vcm = [ViewControllerModel alloc] init]; 
    vcm.string = @"My String"; 
    viewController2.vcm = vcm; 

    NSLog(@"%@",vcm.string) // this will output a number 
    [self.navigationController pushViewController:viewController2 animated:YES]; 
} 

// this delegate fetches an array of json data 
- (void)fetchedResults:(NSMutableArray*)arrayList{ 
    self.array = arrayList; 
} 

ViewController2.h

@interface ViewController2 : NSObject 
@property (nonatomic, strong) ViewControllerModel *vcm; 
@end 

ViewController2.m

- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 
    NSLog(@"%@", self.vcm.string); 
} 

我也建議了以下改進。

1. 此時您並不需要模型對象。您可以將字符串作爲NSString屬性添加到ViewController2而不是ViewControllerModel對象：

   @property（nonatomic，copy）NSString * string;

2. 我建議將您的屬性，模型對象和視圖控制器命名爲更具描述性的內容。即使這是一個樣本，如果你不這樣做，也很難理解它。

3. 當您創建一個NSString屬性（或任何其他具有可變等價物的類）時，我建議使用'copy'而不是'strong'。如果將一個NSMutableString分配給屬性被認爲是更安全的方法，這將會創建一個不可變的字符串副本。