在AndroidManifest.xml中加入一句

<uses-permission android:name="android.permission.INTERNET"/>

<uses-permission android:name="android.permission.INTERNET"/>
    <application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:name=".MyApplication"
 
android:supportsRtl="true"
android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>