iphone中的多級導航xcode 4.2

Question

我在xcode 4.2中創建了一個基於視圖的項目，我想實現多級導航以導航到不同的視圖。我的第一個視圖類是ViewController，我顯示一個表。在點擊一行時，我會去下一個有tabbar的班級。在這個我有3個選項卡。第一個選項卡使用的是BuyerViewController類。它有4個按鈕。問題是，當我點擊按鈕時，它不會推下一個課程。

ViewController.m

- (void)viewDidLoad 
{ 
self.title=@"Select County"; 
    tView = [[UITableView alloc] init]; //tView is my table view object. 
    tView.frame=CGRectMake(0, 20, 320, 460); 
    [tView setDelegate:self]; 
    [tView setDataSource:self]; 
    [self.view addSubview:tView]; 
} 
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { 
return 1; 
} 
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { 
return [countyArray count]; 
} 
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { 

static NSString *CellIdentifier = @"Cell"; 

UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; 
if (cell == nil) { 
    cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease]; 
} 
cell.textLabel.text = [countyArray objectAtIndex:indexPath.row]; 
return cell; 
} 
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { 
//This works fine and pushes to my next class to show the tabs. 

ShowOptionInTab *showTabbar = [[ShowOptionInTab alloc] initWithNibName:@"ShowOptionInTab" bundle:nil]; 
[self.navigationController pushViewController:showTabbar animated:YES]; 
[showTabbar release]; 
} 

ShowOptionInTab.m

-(void)loadView { 
UIView *contentView = [[UIView alloc] initWithFrame:[[UIScreen mainScreen] applicationFrame]]; 
contentView.backgroundColor = [UIColor whiteColor]; 
self.view = contentView; 
[contentView release]; 

BuyerViewController *buyerController = [[BuyerViewController alloc] init ]; 

SellerViewController *sellerController = [[SellerViewController alloc] init]; 

LenderViewController *lenderController = [[LenderViewController alloc] init]; 

buyerController.title=@"Buyer"; 
sellerController.title = @"Seller"; 
lenderController.title = @"Lender"; 

UITabBarController *tabbarController = [[UITabBarController alloc] init]; 

tabbarController.view.frame = CGRectMake(0, 0, 320, 460); 
[tabbarController setViewControllers:[NSArray arrayWithObjects:buyerController, sellerController,lenderController, nil]]; 

[buyerController release]; 
[sellerController release]; 
[lenderController release]; 
[self.view addSubview:tabbarController.view];  
} 

BuyerViewController.m

-(void)viewWillAppear:(BOOL)animated 
{ 
UIButton *quickEstimateButton = [UIButton buttonWithType:UIButtonTypeRoundedRect]; 

    [quickEstimateButton addTarget:self action:@selector(getTagOfPressedButton:) forControlEvents:UIControlEventTouchUpInside]; 
[quickEstimateButton setTitle:@"QUICK ESTIMATE" forState:UIControlStateNormal]; 
quickEstimateButton.tag=1; 
quickEstimateButton.frame = CGRectMake(10, 50, 150, 40.0); 
[self.view addSubview:quickEstimateButton]; 

//more 3 buttons are added in same way 
} 
-(void) getTagOfPressedButton:(id)sender { 

UIButton *getTagOfButton = (UIButton *)sender; 
int buttonPressedTag = getTagOfButton.tag; 
NSLog(@"TAG==========%d",buttonPressedTag); 
if(buttonPressedTag==1) 
{ 
    NSLog(@"quick estimate pressed"); 
    QuickEstimateViewController *q = [[QuickEstimateViewController alloc] init]; 
    NSLog(@"nav====%@",self.navigationController); //This returns null. 
    [self.navigationController pushViewController:q animated:YES]; 
} 
} 

AppDelegate.m

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions 
{ 
     ViewController *overviewViewController = [[ViewController alloc] initWithNibName:@"ViewController_iPhone" bundle:nil]; 
    UINavigationController* navigation = [[UINavigationController alloc] initWithRootViewController:overviewViewController]; 
    navigation.navigationBar.tintColor = [UIColor blackColor]; 
    [overviewViewController release]; 

    [self.window addSubview:[navigation view]]; 
    [self.window makeKeyAndVisible]; 
} 

爲什麼QuickEstimateViewController不顯示？

Answer 1

因爲你在ShowOptionInTab中定義了一個tabBarController的新對象和它的視圖作爲子視圖，然後還定義了一個新的對象BuyerViewController，它試圖推送QuickEstimateViewController的navigationController將是零..我認爲它會工作，如果你的代碼看起來像這樣..

BuyerViewController *buyerController = [[BuyerViewController alloc] init ]; 
UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:buyerController]; 

SellerViewController *sellerController = [[SellerViewController alloc] init]; 

LenderViewController *lenderController = [[LenderViewController alloc] init]; 

buyerController.title=@"Buyer"; 
sellerController.title = @"Seller"; 
lenderController.title = @"Lender"; 

UITabBarController *tabbarController = [[UITabBarController alloc] init]; 

tabbarController.view.frame = CGRectMake(0, 0, 320, 460); 
[tabbarController setViewControllers:[NSArray arrayWithObjects:nav, sellerController,lenderController, nil]];