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-(void)addConstraint:(NSLayoutConstraint *)constraint
•刷新约束的改变
-setNeedsUpdateConstraints
-layoutIfNeeded
[button setTranslatesAutoresizingMaskIntoConstraints:NO];
// 2.1 水平方向的约束 NSLayoutConstraint *constraintX = [NSLayoutConstraint constraintWithItem:button attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1.0f constant:0.0f]; [self.view addConstraint:constraintX]; // 2.2 垂直方向的约束 NSLayoutConstraint *constraintY = [NSLayoutConstraint constraintWithItem:button attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1.0f constant:0.0f]; [self.view addConstraint:constraintY];
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原文地址：http://www.cnblogs.com/qingche/p/4306098.html
