position_of_the_first_component

1.When you use putConstraint(), be sure to specify the unknown component position first and connect it to something that can be calculated or is fixed, like the edge of the screen.
当使用 putConstraint() 时，应首先确信指定了未知组件的位置，并将其连接到某样可以计算的或者固定的东西上，比如屏幕的边界。
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