Autolayout下更新Constraints

// this is Apple's recommended place for adding/updating constraints
- (void)updateConstraints {
    
    [self.movingButton remakeConstraints:^(MASConstraintMaker *make) {
        make.width.equalTo(@(100));
        make.height.equalTo(@(100));
        
        if (self.topLeft) {
            make.left.equalTo(self.left).with.offset(10);
            make.top.equalTo(self.top).with.offset(10);
        }
        else {
            make.bottom.equalTo(self.bottom).with.offset(-10);
            make.right.equalTo(self.right).with.offset(-10);
        }
    }];
    
    //according to apple super should be called at end of method
    [super updateConstraints];
}

- (void)toggleButtonPosition {
    self.topLeft = !self.topLeft;
    
    // tell constraints they need updating
    [self setNeedsUpdateConstraints];
    
    // update constraints now so we can animate the change
    [self updateConstraintsIfNeeded];
    
    [UIView animateWithDuration:0.4 animations:^{
        [self layoutIfNeeded];
    }];
}