Android constraint layout strange behavior

问题

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"/>

回答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.

来源：https://stackoverflow.com/questions/40633299/android-constraint-layout-strange-behavior

标签

android

android-constraintlayout