以编程方式更新约束时获取NSGeneric异常？

Question

这是我的代码：

int x= 17;
int y = 27;
int width = 287;
int height = 181;
int mainview_height = 568;
int x_spacer = 0;
int y_spacer = 0;
int width_spacer = 320;
int height_spacer = 27;

    UIView *view_spacer = [[UIView alloc]initWithFrame:CGRectMake(x_spacer, y_spacer, width_spacer, height_spacer)];
    [view_spacer setBackgroundColor:[UIColor clearColor]];
    [view_spacer setTranslatesAutoresizingMaskIntoConstraints:NO];
    [self.mainView addSubview:view_spacer];
    UIView *view1 = [[UIView alloc]initWithFrame:CGRectMake(x, y, width, height)];
    [view1 setBackgroundColor:[UIColor whiteColor]];
    [view1 setTranslatesAutoresizingMaskIntoConstraints:NO];
    [self.mainView addSubview:view1];

    [view_spacer addConstraint:[NSLayoutConstraint constraintWithItem:view_spacer attribute:NSLayoutAttributeWidth
    relatedBy:NSLayoutRelationEqual toItem:view_spacer attribute:NSLayoutAttributeHeight multiplier:width_spacer/height_spacer constant:0.0f]];
    [self.mainView addConstraint:[NSLayoutConstraint constraintWithItem:view_spacer attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.mainView attribute:NSLayoutAttributeTop multiplier:1 constant:0.0f]];
    [self.mainView addConstraint:[NSLayoutConstraint constraintWithItem:view_spacer attribute:NSLayoutAttributeWidth
    relatedBy:NSLayoutRelationEqual toItem:self.mainView attribute:NSLayoutAttributeHeight multiplier:width_spacer/mainview_height constant:0.0f]];
    [self.mainView addConstraint:[NSLayoutConstraint constraintWithItem:self.mainView attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:view_spacer attribute:NSLayoutAttributeCenterX multiplier:1 constant:0]];
    [view_spacer addConstraint:[NSLayoutConstraint constraintWithItem:view1 attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:view_spacer attribute:NSLayoutAttributeBottom multiplier:1 constant:0.0f]];
    [view1 addConstraint:[NSLayoutConstraint constraintWithItem:view1 attribute:NSLayoutAttributeWidth
                         relatedBy:NSLayoutRelationEqual toItem:view1 attribute:NSLayoutAttributeHeight
                         multiplier:width/height constant:0.0f]];
    [self.mainView addConstraint:[NSLayoutConstraint constraintWithItem:view1 attribute:NSLayoutAttributeWidth
    relatedBy:NSLayoutRelationEqual toItem:self.mainView attribute:NSLayoutAttributeHeight                                                        multiplier:width/mainview_height constant:0.0f]];
    [self.mainView addConstraint:[NSLayoutConstraint constraintWithItem:self.mainView attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:view1 attribute:NSLayoutAttributeCenterX multiplier:1 constant:0]];

更新自动布局约束时出现以下错误

  

未为约束准备视图层次结构：       添加到。时   在视图中，约束的项必须是该视图的后代（或   视图本身）。如果需要约束，这将崩溃   在组装视图层次结构之前解析。打破 - [UIView   _viewHierarchyUnpreparedForConstraint：]进行调试。 2015-07-18 12：54：02.469 LandCorp Cleaning App [2022：64687]查看层次结构   没有准备好限制。约束：       容器   层次结构：＆gt;在容器层次结构中找不到视图：   ＆GT;该视图的超级视图：＆gt; 2015-07-18 12：54：02.472 LandCorp Cleaning   应用程序[2022：64687] *由于未捕获的异常而终止应用程序   'NSGenericException'，原因：'无法在视图上安装约束。   约束是否引用了子树之外的内容   风景？那是违法的。   约束：查看：＆gt;'   * 第一次抛出调用堆栈：（0 CoreFoundation 0x000000010799dc65 exceptionPreprocess + 165 1 libobjc.A.dylib
  0x0000000107636bb7 objc_exception_throw + 45 2 CoreFoundation
  0x000000010799db9d + [NSException raise：format：] + 205 3 Foundation   0x00000001071c8479 - [NSLayoutConstraint   _addToEngine：integralizationAdjustment：mutualExclusiveConstraints：] + 187 4 UIKit 0x0000000108406786 - [UIView（UIConstraintBasedLayout）_layoutEngine_didAddLayoutConstraint：roundingAdjustment：mutualExclusiveConstraints：]   + 411 5 UIKit 0x0000000108406a14 - [UIView（UIConstraintBasedLayout）_tryToAddConstraintWithoutUpdatingConstraintsArray：roundingAdjustment：mutualExclusiveConstraints：]   + 30 6 UIKit 0x0000000108406b3c - [UIView（UIConstraintBasedLayout）_tryToAddConstraint：roundingAdjustment：mutualExclusiveConstraints：] + 243 7 LandCorp Cleaning App 0x00000001070e7e47 - [InspectionDetails populateDataViews] + 2007 8 LandCorp Cleaning App 0x00000001070e748c - [InspectionDetails   connection：didReceiveData：] + 1404 9 CFNetwork
  0x00000001097dbd6c __65- [NSURLConnectionInternal   _withConnectionAndDelegate：onlyActive：] _ block_invoke + 69 10 CFNetwork 0x00000001097dbd10    - [NSURLConnectionInternal _withConnectionAndDelegate：onlyActive：] + 199 11 CFNetwork 0x00000001097dbe77    - [NSURLConnectionInternal _withActiveConnectionAndDelegate：] + 48 12 CFNetwork 0x00000001097c6089   _ZL30_NSURLConnectionDidReceiveDataP16_CFURLConnectionPK8__CFDatalPKv + 79 13 CFNetwork 0x00000001096a85e0 ___ZN27URLConnectionClient_Classic29_delegate_didReceiveDataArrayEv_block_invoke   + 302 14 CFNetwork 0x0000000109778a71 ___ZN27URLConnectionClient_Classic18_withDelegateAsyncEPKcU13block_pointerFvP16_CFURLConnectionPK33CFURLConnectionClientCurrent_VMaxE_block_invoke_2   + 273 15 CFNetwork 0x00000001096965d6 _ZN19RunloopBlockContext13_invoke_blockEPKvPv + 72 16 CoreFoundation 0x00000001078a4354 CFArrayApplyFunction + 68 17 CFNetwork
  0x0000000109696497 _ZN19RunloopBlockContext7performEv + 133 18   CFNetwork 0x00000001096962d6   _ZN17MultiplexerSource7performEv + 256 19 CFNetwork 0x00000001096960ec _ZN17MultiplexerSource8_performEPv + 72 20   CoreFoundation 0x00000001078d1431   __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION + 17 21 CoreFoundation 0x00000001078c72fd   __CFRunLoopDoSources0 + 269 22 CoreFoundation 0x00000001078c6934 __CFRunLoopRun + 868 23 CoreFoundation
  0x00000001078c6366 CFRunLoopRunSpecific + 470 24图形服务
  0x000000010aec3a3e GSEventRunModal + 161 25 UIKit
  0x0000000107d968c0 UIApplicationMain + 1282 26 LandCorp清洁应用程序   0x00000001070e897f main + 111 27 libdyld.dylib
  0x0000000109f41145 start + 1）libc ++ abi.dylib：终止于   NSException类型的未捕获异常