如何在Android中的来电时关闭设备屏幕？

Question

我正在开发Android应用程序，我想在任何来电期间关闭设备屏幕。

我使用以下代码来检测来电。

public class MyCallReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {

        if (intent.getStringExtra(TelephonyManager.EXTRA_STATE).equals(
                TelephonyManager.EXTRA_STATE_RINGING)) {
            // This code will execute when the phone has an incoming call

            // get the phone number
            String incomingNumber = intent
                    .getStringExtra(TelephonyManager.EXTRA_INCOMING_NUMBER);
            Toast.makeText(context, "Call from:" + incomingNumber,
                    Toast.LENGTH_LONG).show();

            // here I need to setting device screen off

        } else if (intent.getStringExtra(TelephonyManager.EXTRA_STATE).equals(
                TelephonyManager.EXTRA_STATE_IDLE)
                || intent.getStringExtra(TelephonyManager.EXTRA_STATE).equals(
                        TelephonyManager.EXTRA_STATE_OFFHOOK)) {
            // This code will execute when the call is disconnected
            Toast.makeText(context, "Detected call hangup event",
                    Toast.LENGTH_LONG).show();

        }
    }
}

我搜索了this code，关闭了设备屏幕。我在我的代码中实现了它，但没有成功，我还无法在来电期间以编程方式关闭设备屏幕。

有人可以帮我这个吗？

修改：
清单文件是这样的：

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.demo"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="15" />

    <uses-permission android:name="android.permission.READ_PHONE_STATE" />
    <uses-permission android:name="android.permission.WAKE_LOCK" />
    <uses-permission android:name="android.permission.DEVICE_POWER" />
    <uses-permission android:name="android.permission.MODIFY_PHONE_STATE" />


    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.demo.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

        <receiver android:name="com.demo.MyCallReceiver" >
            <intent-filter>
                <action android:name="android.intent.action.PHONE_STATE" />
            </intent-filter>
        </receiver>
    </application>

</manifest>