<resources>

    <!-- Base application theme. -->

    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">     //这个是主题，继承与DarkActionBar

        <!-- Customize your theme here. -->

        <item name="colorPrimary">@color/colorPrimary</item>

        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>

        <item name="colorAccent">@color/colorAccent</item>

    </style>

    <style name="buttonstyle">   //这个为自己添加的

        <item name="android:layout_width">wrap_content</item>

        <item name="android:layout_height">wrap_content</item>

        <item name="android:text">heihei</item>

    </style>

</resources>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:app="http://schemas.android.com/apk/res-auto"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:orientation="vertical"

    tools:context="sample.android_serialport_api.myapplication.MainActivity">

　　...

    <Button

        style="@style/buttonstyle"   //在这里使用的style

        android:id="@+id/butto6"/>

    <Button

        style="@style/buttonstyle"

        android:id="@+id/butto7"/>

    <Button

        style="@style/buttonstyle"

        android:id="@+id/butto8"/>

</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="sample.android_serialport_api.myapplication">

    <application

        android:allowBackup="true"

        android:icon="@mipmap/ic_launcher"

        android:label="@string/app_name"

        android:roundIcon="@mipmap/ic_launcher_round"

        android:supportsRtl="true"

        android:theme="@style/AppTheme">     //在这里使用的主题

        <activity android:name=".MainActivity">

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>

        </activity>

    </application>

</manifest>