Subtotal of constraintlayout

ConstraintLayout You can reduce the nesting of layouts , The aspect ratio can also be fixed , To a certain extent, it meets the needs of the project , There are a few easily forgotten points , recorded .

1. Fixed aspect ratio

constraintDimensionRatio To make （ Such as ：app:layout_constraintDimensionRatio=”1:3” Indicates that the aspect ratio is 1:3） The following conditions are required for this attribute to take effect ：
1）left ,right ,top ,bottom All four edges need constraints ,bottom The constraint of can be used baseline Instead of .
2） At least one of the width and height is 0dp perhaps -1dp, If it's all 0dp Will be displayed in the maximum range of the parent layout .

2.GuideLine Use

Guideline yes ConstraintLayout Of Guideline Utility classes for helper objects , The helper does not appear on the device , It is defaulted to View.GONE, And it cannot be changed . in addition ,Guideline It's for ConstraintLayout Created , That is, it can only be used for ConstraintLayou Layout .

 <android.support.constraint.Guideline
	android:id="@+id/guide_line_vertical"
	android:layout_width="wrap_content"
	android:layout_height="wrap_content"
	android:orientation="vertical"
	app:layout_constraintGuide_percent="0.5" />

The above is an example of a split line in the middle of a horizontal direction , Here are some instructions ：
vertical Guideline The width is 0, The height is ConstraintLayout Height
level Guideline The width is ConstraintLayout Width , The height is 0
GuideLine It can also be thought of as a view , It can be based on the dp Or percentage , take GuideLine Position in layout , There are three ways to determine the position ：

layout_constraintGuide_begin： Specify a fixed distance from the left or top of the layout (dp)
layout_constraintGuide_end： Specify a fixed distance from the right or bottom of the layout (dp)
layout_constraintGuide_percent： Specify a percentage of the width or height of the layout