关于DevicePolicyManager的有关问题

package t1.yb;import android.app.Activity;import android.app.admin.DeviceAdminReceiver;import android.app.admin.DevicePolicyManager;import android.content.ComponentName;import android.content.Context;import android.content.Intent;import android.os.Bundle;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;public class mainActivity extends Activity {    Button btn1, btn2, btn3;    DevicePolicyManager devicePolicyManager;    ComponentName componentName;    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        btn1 = (Button) findViewById(R.id.btn1);        btn2 = (Button) findViewById(R.id.btn2);        btn3 = (Button) findViewById(R.id.btn3);        devicePolicyManager = (DevicePolicyManager) getSystemService(Context.DEVICE_POLICY_SERVICE);        componentName = new ComponentName(mainActivity.this, lockclass.class);        btn1.setOnClickListener(new OnClickListener() {            @Override            public void onClick(View v) {                if(!devicePolicyManager.isAdminActive(componentName)) {                    Intent intent = new Intent(                            DevicePolicyManager.ACTION_ADD_DEVICE_ADMIN);                    intent.putExtra(DevicePolicyManager.EXTRA_DEVICE_ADMIN,                            componentName);                    intent.putExtra(DevicePolicyManager.EXTRA_ADD_EXPLANATION,                            "(可自定义区域2)");                    startActivityForResult(intent, 1);                }            }        });        btn2.setOnClickListener(new OnClickListener() {            @Override            public void onClick(View v) {                devicePolicyManager.removeActiveAdmin(componentName);            }        });    }    public class lockclass extends DeviceAdminReceiver {    }}

<?xml version="1.0" encoding="utf-8"?><manifest    xmlns:android="http://schemas.android.com/apk/res/android"    package="t1.yb"    android:versionCode="1"    android:versionName="1.0">    <application        android:icon="@drawable/icon"        android:label="@string/app_name">        <activity            android:name=".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=".mainActivity$lockclass"            android:permission="android.permission.BIND_DEVICE_ADMIN">            <meta-data                android:name="android.app.device_admin"                android:resource="@xml/device_admin" />            <intent-filter>                <action                    android:name="android.app.action.DEVICE_ADMIN_ENABLED" />            </intent-filter>        </receiver>    </application>    <uses-sdk        android:minSdkVersion="8" /></manifest> 

<?xml version="1.0" encoding="utf-8"?><device-admin xmlns:android="http://schemas.android.com/apk/res/android">    <uses-policies>        <limit-password />        <watch-login />        <reset-password />        <force-lock />        <wipe-data />    </uses-policies></device-admin>