在视图iOS中心以编程方式设置自动布局

Question

i am new to iOS using blur effect view for whole screen and want to set the auto layout programatically for textfield in centre of the view and my code is :

UIBlurEffect *blurEffect = [UIBlurEffect effectWithStyle:UIBlurEffectStyleDark];
blurEffectView = [[UIVisualEffectView alloc] initWithEffect:blurEffect];
[blurEffectView setFrame:self.view.bounds];
[self.view addSubview:blurEffectView];

// Vibrancy effect
UIVibrancyEffect *vibrancyEffect = [UIVibrancyEffect effectForBlurEffect:blurEffect];
UIVisualEffectView *vibrancyEffectView = [[UIVisualEffectView alloc] initWithEffect:vibrancyEffect];
[vibrancyEffectView setFrame:self.view.bounds];

UITextField *EmailTextField = [[UITextField alloc] init;
vibrancyEffectView.translatesAutoresizingMaskIntoConstraints = NO;
NSArray *heightConstraint = [NSLayoutConstraint      constraintsWithVisualFormat:@"V:[EmailTextField(30)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(EmailTextField)];
NSArray *widthConstraint = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[EmailTextField(240)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(EmailTextField)];
NSArray *xConstraint = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-42-[EmailTextField(240)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(EmailTextField)];
NSArray *yConstraint = [NSLayoutConstraint constraintsWithVisualFormat:@"V:-150-[EmailTextField(30)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(EmailTextField)];
EmailTextField.textColor = [UIColor redColor];
EmailTextField.font = [UIFont fontWithName:@"Helvetica" size:16];
EmailTextField.backgroundColor=[UIColor clearColor];
EmailTextField.borderStyle = UITextBorderStyleRoundedRect;
[EmailTextField.layer setCornerRadius:10.0f];
EmailTextField.layer.borderWidth = 1.0;
EmailTextField.layer.borderColor = [UIColor whiteColor].CGColor;
EmailTextField.placeholder=@"Email ID";
EmailTextField.textAlignment= NSTextAlignmentCenter;
[[vibrancyEffectView contentView] addSubview:EmailTextField];
[[blurEffectView contentView] addSubview:vibrancyEffectView];
[vibrancyEffectView addConstraints:widthConstraint];
[vibrancyEffectView addConstraints:heightConstraint];
[vibrancyEffectView addConstraints:xConstraint];
[vibrancyEffectView addConstraints:yConstraint];

but gives error :

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unable to parse constraint format: Unable to interpret '|' character, because the related view doesn't have a superview H:|-42-[EmailTextField(240)]

I want two solutions- 1.Please correct the code for the same x=42,y=150 positions of the textfield 2.Texfield in centre of the view.

Thanks in advance if any one could help me with the correct code

Answer 1

You must add your views to the superview before being able to set constraints in the way you have tried to, ie

[[vibrancyEffectView contentView] addSubview:EmailTextField];

Needs to be before your constraintsWithVisualFormat:options:metrics:views: calls.

Here is a nice link explaining the format code well: http://commandshift.co.uk/blog/2013/01/31/visual-format-language-for-autolayout/

Also, you don't need to specify separate constraints for the width and height because you specify these in the subsequent constraints on position.

If you want to centre the text field in the view, then use the explicit constraint setting method, which is very clear (if more verbose!):

[NSLayoutConstraint constraintWithItem:EmailTextField
                             attribute:NSLayoutAttributeCenterX
                             relatedBy:NSLayoutRelationEqual                                                             
                                toItem:[vibrancyEffectView contentView]
                             attribute:NSLayoutAttributeCenterX 
                            multiplier:1 
                              constant:0];

for the horizontal centre and similarly for the vertical centre.

Answer 2

EmailTextField.center = CGPointMake( self.view.bounds.size.width / 2, your Y); Use this