Android阅读电话状态？

我的课 ：

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.telephony.PhonestateListener;
import android.telephony.TelephonyManager;
import android.widget.TextView;

public class TelephonyDemo extends Activity {
    TextView textout;
    TelephonyManager telephonyManager;
    PhonestateListener listener;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        // Get the UI
        textout = (TextView) findViewById(R.id.textout);

        // Get the telephony manager
        telephonyManager = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);

        // Create a new PhonestateListener
        listener = new PhonestateListener() {
            @Override
            public void onCallStateChanged(int state,String incomingNumber) {
                String stateString = "N/A";
                switch (state) {
                case TelephonyManager.CALL_STATE_IDLE:
                    stateString = "Idle";
                    break;
                case TelephonyManager.CALL_STATE_OFFHOOK:
                    stateString = "Off Hook";
                    break;
                case TelephonyManager.CALL_STATE_RINGING:
                    stateString = "Ringing";
                    break;
                }
                textout.append(String.format("\nonCallStateChanged: %s",stateString));
            }
        };

        // Register the listener with the telephony manager
        telephonyManager.listen(listener,PhonestateListener.LISTEN_CALL_STATE);
    }
}

我的清单是：

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.marakana"
    android:versionCode="1"
    android:versionName="1.0" >

    <application
        android:icon="@drawable/icon"
        android:label="@string/app_name"
        android:theme="@android:style/Theme.Light" >
        <activity
            android:name=".TelephonyDemo"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

    <uses-sdk android:minSdkVersion="7" />

</manifest>

我的布局是：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Telephony Demo"
        android:textSize="22sp" />

    <TextView
        android:id="@+id/textout"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Output" >
    </TextView>

</LinearLayout>