只是添加一个与其他两个相关视图位于同一父视图中的视图。
self.vDist = [[UILabel alloc] initWithFrame:CGRectMake(20, 20, 42, 21)];
[self.vDist setTranslatesAutoresizingMaskIntoConstraints:NO];
[self.view addSubview:self.vDist];
NSLayoutConstraint *lc;
lc = [NSLayoutConstraint constraintWithItem:self.vDist attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1.0 constant:20.0];
[self.view addConstraint:lc];
lc = [NSLayoutConstraint constraintWithItem:self.vDist attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1.0 constant:20.0];
[self.view addConstraint:lc];
然后，我在顶部创建小方形视图
/*********************** video view */
self.videoView = [[UIView alloc] initWithFrame:CGRectMake(90, 20, 140, 140)];
[self.videoView setBackgroundColor:[UIColor greenColor]];
[self.videoView setTranslatesAutoresizingMaskIntoConstraints:NO];
[self.view addSubview:self.videoView];
// width & height constraints, as UIViews don't have intrinsic constraints
lc = [NSLayoutConstraint constraintWithItem:self.videoView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:140.0];
[self.videoView addConstraint:lc];
lc = [NSLayoutConstraint constraintWithItem:self.videoView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:140.0];
[self.videoView addConstraint:lc];
// center constraint
lc = [NSLayoutConstraint constraintWithItem:self.videoView attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0.0];
[self.view addConstraint:lc];
// top constraint with its parent view
lc = [NSLayoutConstraint constraintWithItem:self.videoView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1.0 constant:20.0];
[self.view addConstraint:lc];
此方形视图在任何设备方向上都可以显示
现在我在屏幕下部创建第二个视图。它的尺寸在这里并不重要，因为我为每个尺寸属性创建了一个约束
/*********************** listado view */
self.listadoView = [[UIView alloc] initWithFrame:CGRectMake(5, 248, 310, 100)];
[self.listadoView setTranslatesAutoresizingMaskIntoConstraints:NO];
[self.listadoView setBackgroundColor:[UIColor whiteColor]];
[self.view addSubview:self.listadoView];
// height and width constraints as UIView don't have intrinsic constraints
lc = [NSLayoutConstraint constraintWithItem:self.listadoView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:310];
[self.listadoView addConstraint:lc];
lc = [NSLayoutConstraint constraintWithItem:self.listadoView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:300];
// make it weak to be able to squeeze contents
lc.priority = 250;
[self.listadoView addConstraint:lc];
// top with videoView's bottom
lc = [NSLayoutConstraint constraintWithItem:self.listadoView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationLessThanOrEqual toItem:self.videoView attribute:NSLayoutAttributeBottom multiplier:1.0 constant:88.0];
[self.view addConstraint:lc];
// top with parent's view top
lc = [NSLayoutConstraint constraintWithItem:self.listadoView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1.0 constant:248.0];
[self.view addConstraint:lc];
// center constraint
lc = [NSLayoutConstraint constraintWithItem:self.listadoView attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0.0];
[self.view addConstraint:lc];
试图在这里复制 IB 对另一个视图中的约束所做的事情
lc = [NSLayoutConstraint constraintWithItem:self.listadoView attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1.0 constant:5];
[self.view addConstraint:lc];
lc = [NSLayoutConstraint constraintWithItem:self.listadoView attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1.0 constant:10];
[self.view addConstraint:lc];
生成的屏幕在绿色方块下方。垂直的绿色屏幕显示了我的预期（见下面的黄色图像），但在绿色水平中，如您所见，listadoView 的底部边缘低于屏幕边缘，即使我正在设置所有IB 为黄色设置的约束，以及我在黄色中设置的约束。
关于如何设置约束的任何建议？......也许它们的创建顺序与它有关？，因为有时我删除了一个约束并且它起作用了，然后我重新添加了那个约束并且仍然工作！在所有约束下再次运行它，然后停止工作（什么？！）。并且很难成功地重现它以提交错误，但它发生了。
我已经在 iOS5.1 和 6.x 下的 XCode 4.6 和 iOS6.1 下的 xCode 5 中测试了这段代码。
