ios - 自动布局 + UIScrollView 和单个 subview

Question

只是玩弄自动布局和 UIScrollView。我在这里错过了什么？这会在屏幕底部显示一个蓝色的 scrollView，但我看不到 contentView。 View 调试器也无话可说。有任何想法吗？

//
//  ViewController.m
//  Fit
//
//  Created by Adam Dahan on 2015-03-13.
//  Copyright (c) 2015 Adam Dahan. All rights reserved.
//

#import "ViewController.h"

@interface ViewController ()
{
    UIScrollView *scrollView;
    UIView *contentView;
}
@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    [self createViews];
    [self constrainScrollView];
    [self constrainContentView];
}

- (void)createViews
{
#pragma Initialize a scrollView
    scrollView = [[UIScrollView alloc] initWithFrame:CGRectZero];
    scrollView.translatesAutoresizingMaskIntoConstraints = NO;
    scrollView.backgroundColor = [UIColor blueColor];
    scrollView.showsHorizontalScrollIndicator = NO;
    scrollView.showsVerticalScrollIndicator = NO;
    [self.view addSubview:scrollView];

#pragma Initialize a contentView for the scrollView
    contentView = [[UIView alloc] initWithFrame:CGRectZero];
    contentView.backgroundColor = [UIColor redColor];
    contentView.translatesAutoresizingMaskIntoConstraints = NO;
    [scrollView addSubview:contentView];
}

- (void)constrainScrollView
{

#pragma scrollView vertical constraints
    NSArray *cns = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[scrollView(40)]|"
                                                       options:0
                                                       metrics:nil
                                                                views:NSDictionaryOfVariableBindings(scrollView)];
    [self.view addConstraints:cns];

#pragma scrollView horizontal constraints
    cns = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[scrollView]|"
                                              options:0
                                              metrics:nil
                                                views:NSDictionaryOfVariableBindings(scrollView)];
    [self.view addConstraints:cns];
}

- (void)constrainContentView
{

#pragma contentView vertical constraints
    NSArray *cns = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|[contentView]|"
                                              options:0
                                              metrics:nil
                                                views:NSDictionaryOfVariableBindings(scrollView, contentView)];
    [scrollView addConstraints:cns];

#pragma contentView horizontal constraints
    cns = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|[contentView]|"
                                              options:0
                                              metrics:nil
                                                views:NSDictionaryOfVariableBindings(scrollView, contentView)];
    [scrollView addConstraints:cns];
}

@end

Answer 1

使用自动布局时， ScrollView 会稍微复杂一些。框架是根据其他 View 的约束定义的(因为您将是在 constainScrollView 方法中添加的 View )。

但是 contentSize 是根据 scrollView 内部 View 的约束定义的。对于您的情况，contentSize 是 (0,0)，因为内部 View 没有宽度或高度限制。

我想您希望这个内部 View 填充 ScrollView 。那么你的约束应该看起来像这样:

- (void)constrainContentView
{
    [self.view layoutIfNeeded]; // This causes the scrollview width and height to be calculated based on the constraints you sent in the previous method
    // You could check by adding a breakpoint here, if the scrollview has the frame you would expect

#pragma contentView vertical constraints
    NSArray *cns = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-[contentView(height)]-|"
                                              options:0
                                              metrics:@{"height":@(CGRectGetHeight(scrollView.frame))}
                                                views:NSDictionaryOfVariableBindings(scrollView, contentView)];
    [scrollView addConstraints:cns];

#pragma contentView horizontal constraints
    cns = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-[contentView(width)]-|"
                                              options:0
                                              metrics:@{"width":@(CGRectGetWidth(self.view.frame))}
                                                views:NSDictionaryOfVariableBindings(scrollView, contentView)];
    [scrollView addConstraints:cns];
}

您为 width 和 height 设置的实际值取决于您的需要。

重要的是 scrollView 内的 View 需要以这样的方式设置约束，以便可以毫无歧义地计算 contentSize。这意味着如果 View 没有固有大小(如 UIButton 或 UILabel)，您需要显式添加宽度/高度约束。

由于显式设置宽度和高度，在方向更改时您需要更新约束，以便内部 View 具有正确的尺寸。

希望这能解决您的问题。