Android constraint layout strange behavior

Question

The version of my constraint layout is 1.0.0-alpha8 . After I have included a toolbar in my layout , there is space in both left and right side of the toolbar, like the image below

Here is the code for my toolbar

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.Toolbar
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="?attr/actionBarSize"
    android:background="@color/colorPrimary">


</android.support.v7.widget.Toolbar>

Which I have included in my layout in following way

<include
    layout="@layout/toolbar_top"
    android:id="@+id/topPanel"
    android:layout_height="wrap_content"
    android:layout_width="match_parent"/>

I didn't used any additional padding or margin in my root element of the layout file .

Another stange thing is if I compile or build the program my code automatically changed, like

<include
    layout="@layout/toolbar_top"
    android:id="@+id/topPanel"
    android:layout_height="wrap_content"
    android:layout_width="match_parent"/>

Change to

<include
    layout="@layout/toolbar_top"
    android:id="@+id/topPanel"
    android:layout_height="wrap_content"
    android:layout_width="368dp"/>

And the guideline also add some additional value which I didn't write, like layout_editor_absoluteX automatically added .

<android.support.constraint.Guideline
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/guideline1"
    android:orientation="vertical"
    app:layout_constraintGuide_percent="0.15"
    tools:layout_editor_absoluteX="58dp"/>

Answer 1

First, you should update to ConstraintLayout beta 4.

Now, the root problem you have is that you are using match_parent on the toolbar -- this isn't supported by ConstraintLayout. You need to add:

app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"

and use 0dp instead of match_parent:

<include
    layout="@layout/toolbar_top"
    android:id="@+id/topPanel"
    android:layout_height="wrap_content"
    android:layout_width="0dp"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"/>

Note that you can create those attributes easily by doing right-click on the component, and picking

On Android Studio 2.2 you need to hold the key to create the constraints, on Android Studio 2.3 it creates the constraints by default.