converting match_parent to “0dp”

问题

When I use android:layout_height="match_parent" or android:layout_width="match_parent" as height/width of children in Constraint Layout and build the Gradle file it automatically changes to android:layout_height="0dp" or android:layout_widtht="0dp" respectively.

Technically there is a huge difference between 0dp and match_parent.

Most of the time it doesn't effect my layout but sometimes this thing completely destroy my Constraint Layout.

I don't know why this happens.
Please guide me.

回答1:

match_parent isn't supported in ConstraintLayout. If you want the same behavior, use 0dp and set constraints on each side to the parent.

回答2:

You should not use match_parent for any view in a ConstraintLayout. Instead use "match constraints" (0dp)

match_parent means filling whats left where as 0dp means match constraints. In ConstraintLayout, match_parent is not supported.

match_parent relies on it's parent for it's position (x,y & width/height) but 0dp can be defined by a constraint/position

回答3:

The way worked with me for putting a Relative item, under another element, with width matching parent is:

<RelativeLayout
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@id/xxx"
    app:layout_constraintEnd_toEndOf="@+id/xxx"
    >

来源：https://stackoverflow.com/questions/40126678/converting-match-parent-to-0dp