iOS Autolayout 约束设置【顺序】的重要性！

0x00 顺序不同，结果不同

看图说话 1

代码是这样滴~
设置好约束，让 4 个按钮，宽度均分~
结果如上图

    [_pastButton.topAnchor constraintEqualToAnchor:_textView.bottomAnchor constant:6].active = YES;[_pastButton.leftAnchor constraintEqualToAnchor:_textView.leftAnchor].active = YES;[_pastButton.heightAnchor constraintEqualToConstant:44].active = YES;NSArray *buttons = @[_pastButton, _deleteButton, _breakButton, _inputButton];for (NSInteger i = 0; i < buttons.count-1; i++) {UIButton *button1 = buttons[i];UIButton *button2 = buttons[i+1];[button2.topAnchor constraintEqualToAnchor:button1.topAnchor].active = YES;[button2.leftAnchor constraintEqualToAnchor:button1.rightAnchor constant:10].active = YES;[button2.heightAnchor constraintEqualToAnchor:button1.heightAnchor].active = YES;[button2.widthAnchor constraintEqualToAnchor:button1.widthAnchor].active = YES;if (i == buttons.count-1) {[button2.rightAnchor constraintEqualToAnchor:_textView.rightAnchor].active = YES;}}

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看图说话 2

代码是这样滴~
设置好约束，让 4 个按钮，宽度均分~
结果如上图，完美!

    [_pastButton.topAnchor constraintEqualToAnchor:_textView.bottomAnchor constant:6].active = YES;[_pastButton.leftAnchor constraintEqualToAnchor:_textView.leftAnchor].active = YES;[_pastButton.heightAnchor constraintEqualToConstant:44].active = YES;[_inputButton.rightAnchor constraintEqualToAnchor:_textView.rightAnchor].active = YES;NSArray *buttons = @[_pastButton, _deleteButton, _breakButton, _inputButton];for (NSInteger i = 0; i < buttons.count-1; i++) {UIButton *button1 = buttons[i];UIButton *button2 = buttons[i+1];[button2.topAnchor constraintEqualToAnchor:button1.topAnchor].active = YES;[button2.leftAnchor constraintEqualToAnchor:button1.rightAnchor constant:10].active = YES;[button2.heightAnchor constraintEqualToAnchor:button1.heightAnchor].active = YES;[button2.widthAnchor constraintEqualToAnchor:button1.widthAnchor].active = YES;}

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0x02 代码区别

图 1 的代码，是在最后一步添加，最后一个按钮，的右侧约束

        if (i == buttons.count-1) {[button2.rightAnchor constraintEqualToAnchor:_textView.rightAnchor].active = YES;}

图 2 的代码，是在开始添加，最后一个按钮，的右侧约束

        [_inputButton.rightAnchor constraintEqualToAnchor:_textView.rightAnchor].active = YES;

可见，
约束设置的顺序，是多么滴重要！

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0x03 我的小作品

欢迎体验我的作品之一：小五笔 86 版
五笔学习好帮手
App Store 搜索即可~

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