NSLayoutConstraint導致編程工具欄不顯示

Question

我有一個編程UIToolBar是創建和繪製在我的某個ViewController的viewWillAppear:方法。我有NSLayoutConstraint設置，以保持我的工具欄在我的屏幕底部，它適用於iPhone 4s和5s。這裏是我的代碼：

- (void)viewWillAppear:(BOOL)animated 
{ 
    keyboardSuggestionsOpen = NO; 

    //Create custom UIToolBar 
    commentToolBar = [[UIToolbar alloc] init]; 
    commentToolBar.frame = CGRectMake(0, 0, self.view.frame.size.width, 44); //108 


    //[self.view removeConstraints:self.view.constraints]; 
    //Remove all contraints on the toolbar 
    for(NSLayoutConstraint *c in self.view.constraints) 
     if(c.firstItem == commentToolBar || c.secondItem == commentToolBar) 
      [self.view removeConstraint:c]; 

    [self.view setTranslatesAutoresizingMaskIntoConstraints:YES]; 
    [self.commentToolBar setTranslatesAutoresizingMaskIntoConstraints:NO]; 


    commentToolBar.backgroundColor = [UIColor blackColor]; 
    commentToolBar.tintColor = [UIColor blackColor]; 
    commentToolBar.barStyle = UIBarStyleBlackOpaque; 

    //self.commentToolBar.translatesAutoresizingMaskIntoConstraints = YES; 
    //self.commentsContainerView.translatesAutoresizingMaskIntoConstraints = YES; 

    [commentTextView setFont:[UIFont systemFontOfSize:22]]; 
    commentTextView.textAlignment = NSTextAlignmentLeft; 
    commentTextView = [[UITextView alloc] initWithFrame:CGRectMake(0, 0, 205, 35)]; 
    [commentTextView setBackgroundColor:[UIColor whiteColor]]; 
    [commentTextView.layer setCornerRadius:4.0f]; 

    UIBarButtonItem *textViewItem = [[UIBarButtonItem alloc] initWithCustomView:commentTextView]; 

    commentTextView.delegate = self; 
    [commentTextView setReturnKeyType:UIReturnKeyDone]; 

    commentButton = [UIButton buttonWithType:UIButtonTypeCustom]; 
    [commentButton setFrame:CGRectMake(0, 0, 75, 35)]; 
    [commentButton.layer setMasksToBounds:YES]; 
    [commentButton.layer setCornerRadius:4.0f]; 
    [commentButton.layer setBorderWidth:0.75f]; 
    [commentButton.layer setBackgroundColor:[[UIColor colorWithHexString:@"669900"]CGColor]]; 
    [commentButton setTitle:@"Comment" forState:UIControlStateNormal]; 
    commentButton.titleLabel.font = [UIFont systemFontOfSize:14.0f]; 
    [commentButton setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal]; 
    [commentButton addTarget:self action:@selector(commentButtonInvoked:) forControlEvents:UIControlEventTouchUpInside]; 

    commentTextView.textColor = [UIColor lightGrayColor]; 
    commentTextView.text = @"Comment.."; 

    UIBarButtonItem *flexSpace = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:self action:nil]; 

    UIBarButtonItem *commentButtonItem = [[UIBarButtonItem alloc] initWithCustomView:commentButton]; 
    [commentButtonItem setStyle:UIBarButtonItemStylePlain]; 

    [self.commentToolBar setItems:[NSArray arrayWithObjects: textViewItem,flexSpace,commentButtonItem, nil] animated:YES]; 

    [self.view addSubview:commentToolBar]; 


    NSDictionary* views = NSDictionaryOfVariableBindings(commentToolBar); 
    NSString *format = @"V:[commentToolBar(==44)]-|"; 
    NSArray *constraints = [NSLayoutConstraint constraintsWithVisualFormat:format 
                  options:0 
                  metrics:nil 
                  views:views]; 

    [self.view layoutSubviews]; 

    [self.view addConstraints:constraints]; 
} 

正如你可以看到我剛剛編程方式添加的TextView的和按鈕到工具欄。問題是，當它加載.. 工具欄甚至似乎不存在（它是缺席/不可見），我的按鈕根本沒有出現，但我知道textView是在因爲它出現在它應該在的底部。難道我做錯了什麼？

PS - 我已經提供了照片和一些更多的方法，可能是相關的，以我的UIToolBar

這的加載/能見度是什麼樣子加載後：

Answer 1

問題在於您在工具欄上的約束不足。你提供了它的高度和垂直位置，但你沒有提到它應該水平放置的位置。因此，它最終無處可逃。當視圖根本無法出現在界面中時，通常會引起人們的注意力不足（模糊），因此您的情況也是如此。