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Center UIView vertically in scroll view when its dynamic Labels are small enough, but align it to the top once they are not

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I have a view with 3 dynamic labels inside it and I am trying to find a way to centre it vertically in a scroll view but when its dynamic labels are too large to fit on a page, make the text start from the top. What Xcode is doing at the moment is this:

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What I am trying to do is this:

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Any ideas about how to achieve this? Thanks.

like image 821
CristianMoisei Avatar asked Jun 08 '18 18:06

CristianMoisei


1 Answers

You can accomplish this by embedding the labels in a stack view and embedding the stack view in a UIView. The label text will expand the stack view vertically, which will expand the content view vertically, which will control the scroll view's .contentSize.

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Black is the scroll view; blue is the content view; stack view only shows as thin gray outline; labels are yellow, green and cyan. The background colors just make it easier to see what's what.

Bunch of steps, but should be clear:

  • add a scrollView, set constraints as normal
  • add a UIView to scrollView - name it "contentView"
  • set constraints 0 for top/leading/trailing/bottom of contentView to scrollView
  • set width and height of contentView equal to width and height of scrollView
  • add a stackView to contentView
  • set stackView to Vertical / Fill / Fill / Spacing: 20
  • set stackView constraints top: 8, bottom: 8, leading: 40, trailing: 40 to contentView
  • set stackView centerY constraint to contentView
  • add three labels to stackView
  • set fonts and text, set number of lines = 0 for center and bottom labels
  • change stackView top and bottom constraints to >= 8
  • change contentView height constraint to Priority: 250
  • I think that's everything....

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Setting the height Priority of the contentView to 250 will allow it to expand vertically based on the text in the labels.

Setting top and bottom stackView constraints to >= 8 will "push" the top and bottom of the contentView, but allow extra space when you don't have enough text to exceed the vertical bounds.

Results:

enter image description here enter image description here

Here's a storyboard with everything in place for reference:

<?xml version="1.0" encoding="UTF-8"?> <document type="com.apple.InterfaceBuilder3.CocoaTouch.Storyboard.XIB" version="3.0" toolsVersion="14109" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES" useSafeAreas="YES" colorMatched="YES" initialViewController="SeU-GX-TTY">     <device id="retina4_7" orientation="portrait">         <adaptation id="fullscreen"/>     </device>     <dependencies>         <deployment identifier="iOS"/>         <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="14088"/>         <capability name="Safe area layout guides" minToolsVersion="9.0"/>         <capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>     </dependencies>     <scenes> <!--View Controller-->         <scene sceneID="bCz-Kd-LLi">             <objects>                 <viewController id="SeU-GX-TTY" sceneMemberID="viewController">                     <view key="view" contentMode="scaleToFill" id="qjW-fW-J5n">                         <rect key="frame" x="0.0" y="0.0" width="375" height="667"/>                         <autoresizingMask key="autoresizingMask" widthSizable="YES" heightSizable="YES"/>                         <subviews>                             <scrollView clipsSubviews="YES" multipleTouchEnabled="YES" contentMode="scaleToFill" translatesAutoresizingMaskIntoConstraints="NO" id="Zj2-9M-SP5" userLabel="scrollView">                                 <rect key="frame" x="0.0" y="40" width="375" height="627"/>                                 <subviews>                                     <view contentMode="scaleToFill" translatesAutoresizingMaskIntoConstraints="NO" id="Pmb-IH-ckB" userLabel="contentView">                                         <rect key="frame" x="0.0" y="0.0" width="375" height="627"/>                                         <subviews>                                             <stackView opaque="NO" contentMode="scaleToFill" axis="vertical" spacing="20" translatesAutoresizingMaskIntoConstraints="NO" id="EfQ-93-hcI" userLabel="stackView">                                                 <rect key="frame" x="40" y="164" width="295" height="299.5"/>                                                 <subviews>                                                     <label opaque="NO" userInteractionEnabled="NO" contentMode="left" horizontalHuggingPriority="251" verticalHuggingPriority="251" verticalCompressionResistancePriority="751" text="Anger" textAlignment="natural" lineBreakMode="tailTruncation" baselineAdjustment="alignBaselines" adjustsFontSizeToFit="NO" translatesAutoresizingMaskIntoConstraints="NO" id="Sxz-f7-zjR" userLabel="topLabel">                                                         <rect key="frame" x="0.0" y="0.0" width="295" height="43"/>                                                         <color key="backgroundColor" red="0.99953407049999998" green="0.98835557699999999" blue="0.47265523669999998" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>                                                         <fontDescription key="fontDescription" type="system" pointSize="36"/>                                                         <nil key="textColor"/>                                                         <nil key="highlightedColor"/>                                                     </label>                                                     <label opaque="NO" userInteractionEnabled="NO" contentMode="left" horizontalHuggingPriority="251" verticalHuggingPriority="251" textAlignment="natural" lineBreakMode="tailTruncation" numberOfLines="0" baselineAdjustment="alignBaselines" adjustsFontSizeToFit="NO" translatesAutoresizingMaskIntoConstraints="NO" id="STy-4u-e1W" userLabel="centerLabel">                                                         <rect key="frame" x="0.0" y="63" width="295" height="183"/>                                                         <color key="backgroundColor" red="0.83216959239999999" green="0.98548370600000001" blue="0.47333085539999997" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>                                                         <string key="text">Anger is an intense emotion defined as a response to a perceived provocation, the invasion of one's boundaries, or a threat. From an evolutionary standpoint, anger servers to mobilise psychological resources in order to address the threat/invasion. Anger is directed at an individual of equal status.</string>                                                         <fontDescription key="fontDescription" type="system" pointSize="17"/>                                                         <nil key="textColor"/>                                                         <nil key="highlightedColor"/>                                                     </label>                                                     <label opaque="NO" userInteractionEnabled="NO" contentMode="left" horizontalHuggingPriority="251" verticalHuggingPriority="251" verticalCompressionResistancePriority="749" text="Based on information from Wikipedia. APA DIctionary of Psycology" textAlignment="natural" lineBreakMode="tailTruncation" numberOfLines="0" baselineAdjustment="alignBaselines" adjustsFontSizeToFit="NO" translatesAutoresizingMaskIntoConstraints="NO" id="u3i-zP-e1M" userLabel="bottomLabel">                                                         <rect key="frame" x="0.0" y="266" width="295" height="33.5"/>                                                         <color key="backgroundColor" red="0.45138680930000002" green="0.99309605359999997" blue="1" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>                                                         <fontDescription key="fontDescription" type="system" pointSize="14"/>                                                         <nil key="textColor"/>                                                         <nil key="highlightedColor"/>                                                     </label>                                                 </subviews>                                             </stackView>                                         </subviews>                                         <color key="backgroundColor" red="0.46202266219999999" green="0.83828371759999998" blue="1" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>                                         <constraints>                                             <constraint firstAttribute="trailing" secondItem="EfQ-93-hcI" secondAttribute="trailing" constant="40" id="4HE-oJ-RE3"/>                                             <constraint firstItem="EfQ-93-hcI" firstAttribute="centerY" secondItem="Pmb-IH-ckB" secondAttribute="centerY" id="H9O-jj-a7A"/>                                             <constraint firstItem="EfQ-93-hcI" firstAttribute="top" relation="greaterThanOrEqual" secondItem="Pmb-IH-ckB" secondAttribute="top" constant="8" id="cKe-DN-Lbn"/>                                             <constraint firstItem="EfQ-93-hcI" firstAttribute="leading" secondItem="Pmb-IH-ckB" secondAttribute="leading" constant="40" id="f4g-6a-VqH"/>                                             <constraint firstAttribute="bottom" relation="greaterThanOrEqual" secondItem="EfQ-93-hcI" secondAttribute="bottom" constant="8" id="meR-gT-OVG"/>                                         </constraints>                                     </view>                                 </subviews>                                 <color key="backgroundColor" red="0.0" green="0.0" blue="0.0" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>                                 <constraints>                                     <constraint firstItem="Pmb-IH-ckB" firstAttribute="top" secondItem="Zj2-9M-SP5" secondAttribute="top" id="HCI-bq-7ur"/>                                     <constraint firstAttribute="trailing" secondItem="Pmb-IH-ckB" secondAttribute="trailing" id="Tdl-c0-GAV"/>                                     <constraint firstItem="Pmb-IH-ckB" firstAttribute="width" secondItem="Zj2-9M-SP5" secondAttribute="width" id="Zj9-ND-Fqt"/>                                     <constraint firstItem="Pmb-IH-ckB" firstAttribute="leading" secondItem="Zj2-9M-SP5" secondAttribute="leading" id="ckv-wi-E1z"/>                                     <constraint firstItem="Pmb-IH-ckB" firstAttribute="height" secondItem="Zj2-9M-SP5" secondAttribute="height" priority="250" id="jpK-HZ-vva"/>                                     <constraint firstAttribute="bottom" secondItem="Pmb-IH-ckB" secondAttribute="bottom" id="psz-UW-bNp"/>                                 </constraints>                             </scrollView>                         </subviews>                         <color key="backgroundColor" white="1" alpha="1" colorSpace="custom" customColorSpace="genericGamma22GrayColorSpace"/>                         <constraints>                             <constraint firstItem="Zj2-9M-SP5" firstAttribute="top" secondItem="Xr7-LW-bbC" secondAttribute="top" constant="20" id="EgA-Bk-3fC"/>                             <constraint firstItem="Zj2-9M-SP5" firstAttribute="leading" secondItem="qjW-fW-J5n" secondAttribute="leading" id="MBG-pL-R8Q"/>                             <constraint firstItem="Xr7-LW-bbC" firstAttribute="bottom" secondItem="Zj2-9M-SP5" secondAttribute="bottom" id="e9K-6A-Y9F"/>                             <constraint firstItem="Xr7-LW-bbC" firstAttribute="trailing" secondItem="Zj2-9M-SP5" secondAttribute="trailing" id="yfs-wt-Br8"/>                         </constraints>                         <viewLayoutGuide key="safeArea" id="Xr7-LW-bbC"/>                     </view>                 </viewController>                 <placeholder placeholderIdentifier="IBFirstResponder" id="lHx-xL-Vx5" userLabel="First Responder" sceneMemberID="firstResponder"/>             </objects>             <point key="canvasLocation" x="225" y="106"/>         </scene>     </scenes> </document> 

And here's a quick example replicating that layout / functionality via code only:

// //  ScrollWorkViewController.swift // //  Created by DonMag on 6/12/19. //  import UIKit  class ScrollWorkViewController: UIViewController {      let theScrollView: UIScrollView = {         let v = UIScrollView()         v.backgroundColor = .red         return v     }()      let contentView: UIView = {         let v = UIView()         v.backgroundColor = UIColor(red: 0.25, green: 0.25, blue: 1.0, alpha: 1.0)         return v     }()      let stackView: UIStackView = {         let v = UIStackView()         v.axis = .vertical         v.alignment = .fill         v.distribution = .fill         v.spacing = 20         return v     }()      let topLabel: UILabel = {         let v = UILabel()         v.font = UIFont.boldSystemFont(ofSize: 32.0)         v.backgroundColor = .yellow         return v     }()      let centerLabel: UILabel = {         let v = UILabel()         v.font = UIFont.systemFont(ofSize: 17.0)         v.numberOfLines = 0         v.backgroundColor = .green         return v     }()      let bottomLabel: UILabel = {         let v = UILabel()         v.font = UIFont.systemFont(ofSize: 14.0)         v.numberOfLines = 0         v.backgroundColor = .cyan         return v     }()      override func viewDidLoad() {         super.viewDidLoad()          [theScrollView, contentView, stackView, topLabel, centerLabel, bottomLabel].forEach {             $0.translatesAutoresizingMaskIntoConstraints = false         }          view.addSubview(theScrollView)         theScrollView.addSubview(contentView)         contentView.addSubview(stackView)         stackView.addArrangedSubview(topLabel)         stackView.addArrangedSubview(centerLabel)         stackView.addArrangedSubview(bottomLabel)          let contentViewHeightConstraint = contentView.heightAnchor.constraint(equalTo: theScrollView.heightAnchor, constant: 0.0)         contentViewHeightConstraint.priority = .defaultLow          NSLayoutConstraint.activate([              // constrain all 4 sides of the scroll view to the safe area             theScrollView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 0.0),             theScrollView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: 0.0),             theScrollView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor, constant: 0.0),             theScrollView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor, constant: 0.0),              // constrain all 4 sides of the content view to the scroll view             contentView.topAnchor.constraint(equalTo: theScrollView.topAnchor, constant: 0.0),             contentView.bottomAnchor.constraint(equalTo: theScrollView.bottomAnchor, constant: 0.0),             contentView.leadingAnchor.constraint(equalTo: theScrollView.leadingAnchor, constant: 0.0),             contentView.trailingAnchor.constraint(equalTo: theScrollView.trailingAnchor, constant: 0.0),              // constrain width of content view to width of scroll view             contentView.widthAnchor.constraint(equalTo: theScrollView.widthAnchor, constant: 0.0),              // constrain the stack view >= 8-pts from the top             // <= minus 8-pts from the bottom             // 40-pts leading and trailing             stackView.topAnchor.constraint(greaterThanOrEqualTo: contentView.topAnchor, constant: 8.0),             stackView.bottomAnchor.constraint(lessThanOrEqualTo: contentView.bottomAnchor, constant: -8.0),             stackView.leadingAnchor.constraint(equalTo: contentView.leadingAnchor, constant: 40.0),             stackView.trailingAnchor.constraint(equalTo: contentView.trailingAnchor, constant: -40.0),              // constrain stack view centerY to contentView centerY             stackView.centerYAnchor.constraint(equalTo: contentView.centerYAnchor, constant: 0.0),              // activate the contentView's height constraint             contentViewHeightConstraint,              ])          topLabel.text = "Anger"         bottomLabel.text = "Based on information from Wikipedia APA Dictionary of Psychology"          // a sample paragraph of text         let centerSampleText = "Anger is an intense emotion defined as a response to a perceived provocation, the invasion of one’s boundaries, or a threat. From an evolutionary standpoint, anger servers to mobilise psychological resources in order to address the threat/invasion. Anger is directed at an individual of equal status."          // change to repeat the center-label sample text         let numberOfParagraphs = 2          var s = ""          for i in 1...numberOfParagraphs {             s += "\(i). " + centerSampleText             if i < numberOfParagraphs {                 s += "\n\n"             }         }          centerLabel.text = s      }  } 
like image 67
DonMag Avatar answered Sep 20 '22 13:09

DonMag