constraintRight_toRightOf与constraintRight_toLeftOf的区别及parent设置对比

Hey there! Let's break down these two AutoLayout constraints clearly—they might look similar but do totally different things when positioning your views.

核心概念差异 #

First, let's get the basic definitions straight:

• constraintRight_toRightOf: This constraint aligns the right edge of your current view with the right edge of another view (like its parent). Think of it as saying: "My right side lines up exactly with your right side".
• constraintRight_toLeftOf: This constraint attaches the right edge of your current view to the left edge of another view. In plain terms: "My right side sticks to your left side".

绑定到父视图(parent)时的实际表现 #

Let's use a concrete example: imagine a parent view that's 300pt wide, and a child view that's 100pt wide.

When setting constraintRight_toRightOf="parent" #

• The child's right edge will perfectly align with the parent's right edge.
• The child's position will be: starting at 300 - 100 = 200pt (x-coordinate, assuming the parent starts at x=0) and extending left 100pt.
• Visually, the child will sit flush against the parent's right inner edge, fully inside the parent.

When setting constraintRight_toLeftOf="parent" #

• The child's right edge will be attached to the parent's left edge.
• By default, this means the child's right edge is at x=0 (the parent's left start), so the child's x-coordinate becomes 0 - 100 = -100pt—the entire child will sit outside the parent, to the left of it.
• You'd usually pair this with an offset (using the constant property, e.g., constraintRight_toLeftOf="parent" constant="20") to pull the child back into the parent, making its right edge sit 20pt inside the parent's left edge. Or combine it with other constraints (like a left edge constraint) to fix its position properly.

A quick note: Neither of these constraints should be used alone—you'll need to pair them with width constraints, top/bottom constraints, or other leading/trailing constraints to avoid layout ambiguity or unexpected view placement.

内容的提问来源于stack exchange，提问作者Smeet Bhatt