$《第一行代码:Android》读书笔记——第5章 Broadcast
(一)广播机制简介
1、Android广播的分类:
如图所示:
2、发送广播:使用Intent;接收广播:Broadcast Receiver。
(二)接收系统广播
1、动态注册监听网络变化
示例程序:
(1)MainActivity(注:以下代码中的ToastUtil是自己简单封装的Toast显示功能的类):
package com.example.broadcasttest; import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem; public class MainActivity extends Activity { private IntentFilter intentFilter;
private NetworkChangeReceiver networkChangeReceiver; @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main); // 1.创建IntentFilter实例
intentFilter = new IntentFilter();
// 2.用addAction方法添加action
intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE"); // 3.创建内部类NetworkChangeReceiver实例
networkChangeReceiver = new NetworkChangeReceiver();
// 4.注册
registerReceiver(networkChangeReceiver, intentFilter);
} class NetworkChangeReceiver extends BroadcastReceiver { @Override
public void onReceive(Context context, Intent intent) {
// 创建ConnectivityManager实例
ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
// 创建NetworkInfo对象(需要申请权限ACCESS_NETWORK_STATE)
NetworkInfo networkInfo = connectivityManager
.getActiveNetworkInfo(); // 判断NetworkInfo的状态,即网络是否可用
if (networkInfo != null && networkInfo.isAvailable()) {
ToastUtil.showShort(MainActivity.this, "网络可用!");
} else {
ToastUtil.showShort(MainActivity.this, "网络不可用!");
} }
} @Override
protected void onDestroy() {
super.onDestroy();
unregisterReceiver(networkChangeReceiver);
} }
(2)申请权限
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
(3)xml文件:不需要添加什么内容。
2、静态注册实现开机启动
动态注册的一个缺点就是,必须要在程序启动之后才能接收到广播,而静态注册就可以在程序还未启动时就能接收到广播,利用这一点就可以实现诸如开机启动程序的功能。
示例程序:
(1)新建类BootCompleteReceiver继承自BroadcastReceiver(注:onReceive方法中红不能放过于耗时的逻辑,因为其中不允许使用线程):
package com.example.broadcasttest; import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent; public class BootCompleteReceiver extends BroadcastReceiver { @Override
public void onReceive(Context context, Intent intent) {
ToastUtil.showShort(context, "BroadcastTest开机启动");
} }
(2)在AndroidManifest.xml静态注册广播:
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
...
<receiver android:name=".BootCompleteReceiver" >
<intent-filter>
<action android:name="android.intent.action.BOOT_COMPLETED" />
</intent-filter>
</receiver>
</application>
(3)申请权限:
<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
(三)发送自定义广播
1、发送标准广播
(1)在BroadcastTest项目中:
①创建MyBroadcastReceiver:
public class MyBroadcastReceiver extends BroadcastReceiver { @Override
public void onReceive(Context context, Intent intent) {
ToastUtil.showShort(context, "在MyBroadcastReceiver中接收到了自定义广播!");
} }
②在AndroidManifest.xml中注册广播接收器:
<receiver android:name=".MyBroadcastReceiver" >
<intent-filter>
<action android:name="com.example.broadcasttest.MY_BROADCAST" />
</intent-filter>
</receiver>
③activity_main.xml:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" > <Button
android:id="@+id/send_broadcast_btn"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="发送自定义广播" /> </LinearLayout>
④MainActivity:
package com.example.broadcasttest; import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button; public class MainActivity extends Activity implements OnClickListener { private Button sendBroadcast; @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main); sendBroadcast = (Button) findViewById(R.id.send_broadcast_btn);
sendBroadcast.setOnClickListener(this);
} @Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.send_broadcast_btn:
Intent intent = new Intent("com.example.broadcasttest.MY_BROADCAST");
sendBroadcast(intent);
break;
default:
break;
}
}
}
(2)创建BroadcastTest2项目,在其中:
①创建AnotherBroadcastReceiver:
public class AnotherBroadcastReceiver extends BroadcastReceiver { @Override
public void onReceive(Context context, Intent intent) {
ToastUtil.showShort(context, "在AnotherBroadcastReceiver中接收到了自定义广播!");
} }
②在AndroidManifest.xml中注册广播接收器:
<receiver android:name=".AnotherBroadcastReceiver" >
<intent-filter>
<action android:name="com.example.broadcasttest.MY_BROADCAST" />
</intent-filter>
</receiver>
(3)同时运行BroadcastTest和BroadcastTest2程序,然后在BroadcastTest中点击“发送自定义广播”按钮,然后就会发现弹出两次Toast显示接收到了广播。
2、发送有序广播
在1中BroadcastTest项目的基础上,做以下修改即可(红色加下划线的代码为新增或修改的代码):
(1)MainActivity中:
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.send_broadcast_btn:
Intent intent = new Intent("com.example.broadcasttest.MY_BROADCAST");
sendOrderedBroadcast(intent, null);
break;
default:
break;
}
}
(2)AndroidManifest.xml中:
<receiver android:name=".MyBroadcastReceiver" >
<intent-filter android:priority="100" >
<action android:name="com.example.broadcasttest.MY_BROADCAST" />
</intent-filter>
</receiver>
(3)MyBroadcastReceiver类中:
public class MyBroadcastReceiver extends BroadcastReceiver { @Override
public void onReceive(Context context, Intent intent) {
ToastUtil.showShort(context, "在MyBroadcastReceiver中接收到了自定义广播!");
abortBroadcast();
} }
(4)再运行两个程序,点击发送广播按钮后,发现只看到了一个Toast提示,因为另一个广播接收被截断了。
(四)使用本地广播
以上的广播都是全局广播,也就是任何应用程序都能接收到。而这会引发安全性问题,如果只希望在当前应用程序内部传递广播,就要使用本地广播了。
本地广播的关键是使用LocalBroadcastManager来发送广播。示例程序:
1、xml文件:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" > <Button
android:id="@+id/send_broadcast_btn"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="发送自定义广播" /> </LinearLayout>
2、MainActivity:
package com.example.broadcasttest; import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;
import android.support.v4.content.LocalBroadcastManager;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button; public class MainActivity extends Activity implements OnClickListener { private Button sendBroadcast; private IntentFilter intentFilter; private LocalReceiver localReceiver;
private LocalBroadcastManager localBroadcastManager; @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main); // 1.获取localBroadcastManager实例
localBroadcastManager = LocalBroadcastManager.getInstance(this); sendBroadcast = (Button) findViewById(R.id.send_broadcast_btn); // 2.在点击事件中用LocalBroadcastManager的sendBroadcast方法发送广播
sendBroadcast.setOnClickListener(this); // 3.注册IntentFilter
intentFilter = new IntentFilter();
intentFilter.addAction("com.example.broadcasttest.LOCAL_BROADCAST");
localReceiver = new LocalReceiver();
localBroadcastManager.registerReceiver(localReceiver, intentFilter);
} @Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.send_broadcast_btn:
Intent intent = new Intent(
"com.example.broadcasttest.LOCAL_BROADCAST");
localBroadcastManager.sendBroadcast(intent);
break;
default:
break;
}
} @Override
protected void onDestroy() {
super.onDestroy();
localBroadcastManager.unregisterReceiver(localReceiver);
}
}
3、注册广播接收器:
<receiver android:name=".LocalReceiver" >
<intent-filter>
<action android:name="com.example.broadcasttest.LOCAL_BROADCAST" />
</intent-filter>
</receiver>
4、这时如果也让另一个程序接收LOCAL_BROADCAST这个广播,会发现是接收不到的。
5、本地广播的优点:
(1)不用担心机密数据泄露。
(2)其他程序无法将广播发送到我们程序的内容,不用担心安全漏洞的问题。
(3)比全局广播更高效。
(五)最佳实践——实现强制下线功能
在登录页面输入账号密码进入主界面后,点击强制下线按钮会弹出强制下线Dialog,并且该Dialog不能被取消,当用户点击确定后会发出强制下线广播,再次跳转到登录界面。
1、login.xml文件:
<?xml version="1.0" encoding="utf-8"?>
<TableLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:stretchColumns="1" > <TableRow> <TextView
android:layout_height="wrap_content"
android:text="用户名:" /> <EditText
android:id="@+id/user_name_et"
android:layout_height="wrap_content"
android:hint="请输入用户名" />
</TableRow> <TableRow> <TextView
android:layout_height="wrap_content"
android:text="密码:" /> <EditText
android:id="@+id/password_et"
android:layout_height="wrap_content" >
</EditText>
</TableRow> <TableRow> <Button
android:id="@+id/login_bt"
android:layout_height="wrap_content"
android:layout_span="2"
android:text="登录" />
</TableRow> </TableLayout>
2、ActivityCollector类:
public class ActivityCollector {
public static List<Activity> activities = new ArrayList<Activity>(); public static void addActivity(Activity activity) {
activities.add(activity);
} public static void removeActivity(Activity activity) {
activities.remove(activity);
} public static void finishAll() {
for (Activity activity : activities) {
if (!activity.isFinishing()) {
activity.finish();
}
}
}
}
3、BaseActivity类:
public class BaseActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState); ActivityCollector.addActivity(this);
} @Override
protected void onDestroy() {
super.onDestroy();
ActivityCollector.removeActivity(this);
}
}
4、LoginActivity类:
public class LoginActivity extends BaseActivity { private EditText userNameEt;
private EditText passwordEt;
private Button loginBt; @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.login); userNameEt = (EditText) findViewById(R.id.user_name_et);
passwordEt = (EditText) findViewById(R.id.password_et);
loginBt = (Button) findViewById(R.id.login_bt); loginBt.setOnClickListener(new OnClickListener() { @Override
public void onClick(View v) {
String userName = userNameEt.getText().toString();
String password = passwordEt.getText().toString(); // 如果用户名是admin且密码是123456,就认为登录成功
if (userName.equals("110") && password.equals("123456")) {
Intent intent = new Intent(LoginActivity.this,
MainActivity.class);
startActivity(intent);
finish();
} else {
Toast.makeText(LoginActivity.this, "用户名或密码错误!",
Toast.LENGTH_SHORT).show();
}
}
});
}
}
5、activity_main.xml:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.broadcastbestpractice.MainActivity" > <TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="这里是主界面" /> <Button
android:id="@+id/force_offline_bt"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="40dp"
android:text="发送一个强制下线广播" /> </RelativeLayout>
6、MainActivity类:
public class MainActivity extends Activity { @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main); Button forceOfflineBt = (Button) findViewById(R.id.force_offline_bt);
forceOfflineBt.setOnClickListener(new OnClickListener() { @Override
public void onClick(View v) {
Intent intent = new Intent(
"com.example.broadcastbestpractice.FORCE_OFFLINE");
sendBroadcast(intent);
}
});
} }
7、ForceOfflineReceiver:
public class ForceOfflineReceiver extends BroadcastReceiver { @Override
public void onReceive(final Context context, Intent intent) {
AlertDialog.Builder dialogBuilder = new AlertDialog.Builder(context);
dialogBuilder.setTitle("警告");
dialogBuilder.setMessage("你将要被强制下线!请重新登录!");
dialogBuilder.setCancelable(false);
dialogBuilder.setPositiveButton("确定",
new DialogInterface.OnClickListener() { @Override
public void onClick(DialogInterface dialog, int which) {
ActivityCollector.finishAll();
Intent intent = new Intent(context, LoginActivity.class);
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
context.startActivity(intent);
}
}); AlertDialog alertDialog = dialogBuilder.create();
alertDialog.getWindow().setType(
WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);
alertDialog.show();
}
}
8、AndroidManifest.xml:
...
<activity
android:name=".LoginActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".MainActivity" >
</activity> <receiver
android:name=".ForceOfflineReceiver"
android:exported="false" >
<intent-filter>
<action android:name="com.example.broadcastbestpractice.FORCE_OFFLINE" />
</intent-filter>
</receiver>
...
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