$avg = array_sum($a) / count($a);

通常，我们还需要把多余的小数去掉：

$avg2 = round($avg, 1);

SharedPreferences prefs = this.getSharedPreferences(
      "com.example.app", Context.MODE_PRIVATE);

读取设置：

String dateTimeKey = "com.example.app.datetime";

// use a default value using new Date()
long l = prefs.getLong(dateTimeKey, new Date().getTime()); 

编辑保存设置：

Date dt = getSomeDate();
prefs.edit().putLong(dateTimeKey, dt.getTime()).apply();

myTextView.setText(Html.fromHtml("<h2>Title</h2><br><p>Description here</p>"));

public boolean isOnline() {
    ConnectivityManager cm =
        (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo netInfo = cm.getActiveNetworkInfo();
    return netInfo != null && netInfo.isConnectedOrConnecting();
}

在AndroidManifest.xml中添加下面权限:

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

Calendar c = Calendar.getInstance();

int seconds = c.get(Calendar.SECOND);

参考：Calendar class documentation

Intent browserIntent = new Intent(Intent.ACTION_VIEW, Uri.parse("http://www.google.com"));

startActivity(browserIntent);

在AndroidManifest.xml的activity里添加android:screenOrientation="portrait"

<activity android:name=".SomeActivity" android:label="@string/app_name" android:screenOrientation="portrait">

一样的。历史问题，API 8+用match_parent就可以了

<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent" 
    android:gravity="center"
    android:text="@string/**yourtextstring**"
/>

CTRL+F12