uiscrollview的自动布局，视图层次结构没有为约束做好准备

Posted 2023-03-08

【中文标题】uiscrollview的自动布局，视图层次结构没有为约束做好准备

【英文标题】：uiscrollview's autolayout,The view hierarchy is not prepared for the constraint

【发布时间】：2015-04-10 04:30:35

【问题描述】：

我想使用自动布局将滚动图像视图添加到滚动视图。

视图层次结构如下：

---|

|---占位符视图

|---滚动视图

代码如下：

-(UICollectionViewCell*)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath

static NSString* identifier = @"WCollectionViewCell";


WCollectionViewCell* cell =[collectionView dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];
cell.imageScrollview.backgroundColor=[UIColor orangeColor];

UIImageView* imageview1 = [[UIImageView alloc]init];
imageview1.image =[UIImage imageNamed:@"1.jpg"];
imageview1.translatesAutoresizingMaskIntoConstraints=NO;
[cell.imageScrollview addSubview:imageview1];

NSDictionary* views = @@"imageview1":imageview1,@"placeview":cell.placeHolderView,@"scrollview":cell.imageScrollview;

//set the imageview'size
NSArray *img_constraint_H = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[imageview1(placeview)]"
                                                                    options:0
                                                                    metrics:nil
                                                                      views:views];

NSArray *img_constraint_V = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[imageview1(placeview)]"
                                                                    options:0
                                                                    metrics:nil
                                                                      views:views];

[self.view addConstraints:img_constraint_H];
[self.view addConstraints:img_constraint_V];


//set the imageview's position
NSArray*  top_position = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-0-[imageview1]"
                                                            options:0 metrics:nil views:views];

NSArray* bottom_position = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-0-[imageview1]"
                                                              options:0 metrics:nil views:views];

[cell.imageScrollview addConstraints:top_position];
[cell.imageScrollview addConstraints:bottom_position];

return cell;

--------错误--------- 2015-04-10 12:20:46.245 T[92361:1319616] 视图层次结构没有为约束做好准备： 添加到视图时，约束的项必须是该视图（或视图本身）的后代。如果在组装视图层次结构之前需要解决约束，这将崩溃。中断 -[UIView _viewHierarchyUnpreparedForConstraint:] 进行调试。 2015-04-10 12:20:46.246 T[92361:1319616] * 断言失败 -[UIView _layoutEngine_didAddLayoutConstraint:roundingAdjustment:mutuallyExclusiveConstraints:], /SourceCache/UIKit_Sim/UIKit-3318.93/NSLayoutConstraint_UIKitAdditions.m:560 2015-04-10 12:20:46.249 T[92361:1319616] * 由于未捕获的异常“NSInternalInconsistencyException”而终止应用程序，原因：“无法设置未准备好约束的视图层次结构的布局。”

【参考方案1】：

您的问题是您将图像的高度和宽度的约束添加到 self.view 这不是图像的父视图。

您需要将约束添加到cell.imageScrollview，这是单元格超级视图或图像本身。

所以这两个都应该工作：

//set the imageview'size
NSArray *img_constraint_H = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[imageview1(placeview)]"
                                                                    options:0
                                                                    metrics:nil
                                                                      views:views];

NSArray *img_constraint_V = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[imageview1(placeview)]"
                                                                    options:0
                                                                    metrics:nil
                                                                      views:views];

[cell.imageScrollview addConstraints:img_constraint_H];
[cell.imageScrollview addConstraints:img_constraint_V];

或

[imageview1 addConstraints:img_constraint_H];
[imageview1 addConstraints:img_constraint_V];

您有两个选项，因为约束不引用父级，只是 imageView。如果视觉格式中有|，则只有第一个选项有效。

另一个提示：

您可以一次添加所有约束：

WCollectionViewCell* cell =[collectionView dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];
cell.imageScrollview.backgroundColor=[UIColor orangeColor];

UIImageView* imageview1 = [[UIImageView alloc]init];
imageview1.image =[UIImage imageNamed:@"1.jpg"];
imageview1.translatesAutoresizingMaskIntoConstraints=NO;
[cell.imageScrollview addSubview:imageview1];

NSDictionary* views = @@"imageview1":imageview1,@"placeview":cell.placeHolderView,@"scrollview":cell.imageScrollview;    
//set the imageview's position
NSArray*  horizontal_constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-0-[imageview1(placeview)]"
                                                            options:0 metrics:nil views:views];

NSArray* vertical_constraints = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-0-[imageview1(placeview)]"
                                                              options:0 metrics:nil views:views];

[cell.imageScrollview addConstraints:horizontal_constraints];
[cell.imageScrollview addConstraints:vertical_constraints];

return cell;

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