Question

AIM

这是我想要做的：

在我的应用程序的所有活动中始终检查互联网连接（到目前为止，我有13项活动）。
如果网络正常工作则一切正常。
如果net无效，请显示一条消息（使用RelativeLayout），该消息将在用户离线时显示，即直到网络再次运行，该消息将在那里（用户访问的任何活动）

以前的尝试

以下是我的尝试：

我尝试创建一个扩展Broadcast Receiver的类。我在所有活动中创建了该类的对象并注册了接收器。
在我的班级中，每当网络状态发生变化时，主类通过Intent向活动发送消息，然后活动接收并检查消息（代码如下）。

问题在于：

我从未取消注册接收器当然给了我一个错误。
```
Are you missing a call to unregisterReceiver()?
```

如果我取消注册接收器，它会给我以下错误：

java.lang.IllegalArgumentException: Receiver not registered

活动中的代码

// The onCreate function (Just a sample)

onCreate(){
            registerReceiver(broadcastReceiver, new IntentFilter("broadCastName"));
}

// Outside OnCreate
NetworkStatus broadcastReceiver =  new NetworkStatus() {
    @Override
    public void onReceive(Context context, Intent intent) {
        String message;
        Bundle b = intent.getExtras();
        message = b.getString(KEY_NET_MESSAGE);

        if (message.equals(KEY_NET_DISCONNECTED)){
            Toast.makeText(SignupActivity.this, MESSAGE_NET_DISCONNECTED, Toast.LENGTH_SHORT).show();
            btnSignup.setEnabled(false);
            Network_disconnection.setVisibility(View.VISIBLE);
        }
        if (message.equals(KEY_NET_CONNECTED)){
            btnSignup.setEnabled(true);
            Network_disconnection.setVisibility(View.INVISIBLE);
        }

    }
};

//onStop, just a sample
@Override
protected void onStop() {
    unregisterReceiver(broadcastReceiver);
    super.onStop();
}

的AndroidManifest.xml

<receiver android:name=".Common.NetworkStatus">
        -
        <intent-filter>
            <action android:name="android.net.conn.CONNECTIVITY_CHANGE" />
        </intent-filter>
    </receiver>

NetworkStatus.java

public class NetworkStatus extends BroadcastReceiver implements Keys.UniversalKeys{

@Override
public void onReceive(Context context, Intent arg1) {

    boolean isConnected = arg1.getBooleanExtra(ConnectivityManager.EXTRA_NO_CONNECTIVITY, false);
    if(isConnected){
        Intent i = new Intent("broadCastName");
        // Data you need to pass to activity
        i.putExtra(KEY_NET_MESSAGE, KEY_NET_DISCONNECTED);

        context.sendBroadcast(i);
    }
    else{

        Intent i = new Intent("broadCastName");
        // Data you need to pass to activity
        i.putExtra(KEY_NET_MESSAGE, KEY_NET_CONNECTED);

        context.sendBroadcast(i);
        Toast.makeText(context, KEY_NET_CONNECTED, Toast.LENGTH_LONG).show();
    }
}
}

问题

我做错了什么？有一点我很清楚，也许我不应该在每个活动上创建新的接收器！另外，为什么我需要制作一个额外的java文件？我的意思是为什么我不能在每个活动上创建一个BroadcastReceiver对象并继续使用它？

Answer 1

了解XML与JAVA

当您在AndroidMainfest.XML中注册接收器时，它是静态的。即使应用程序关闭，它也会运行。

当您在JAVA（活动）中注册接收器时，它是动态的，可以通过动态编码进行注册和注销。

解决方案

使用以下代码创建一个SampleActivity.java类：

public class SampleActivity extends AppCompatActivity {
    // Declare BroadcastReceiver and RelativeLayout
    BroadcastReceiver breceiver;
    RelativeLayout NoNetBar;


    @Override
        protected void onResume() {
            Toast.makeText(SampleActivity.this, "App has Resumed", Toast.LENGTH_SHORT).show();

            // Register your receiver upon resume.
            registerReceiver(breceiver, new IntentFilter("broadCastName"));
            Toast.makeText(SampleActivity.this, "Broadcast Registered", Toast.LENGTH_SHORT).show();
            super.onResume();
        }

        public void setRelative(RelativeLayout param_bar) {
            Toast.makeText(SampleActivity.this, "NoNetBar has been setup", Toast.LENGTH_SHORT).show();
            // This will set RelativeLayout to your desired RelativeLayout from your main activity
            NoNetBar = param_bar;
        }

        @Override
        protected void onCreate(@Nullable Bundle savedInstanceState) {
            // Call super oncreate and then set RelativeLayout to invisible initially
            super.onCreate(savedInstanceState);

            NoNetBar.setVisibility(View.INVISIBLE);

            // Initialize broadcast receiver
            breceiver = new BroadcastReceiver() {
                @Override
                public void onReceive(Context context, Intent intent) {
        boolean isConnected = intent.getBooleanExtra(ConnectivityManager.EXTRA_NO_CONNECTIVITY, false);
                    if (isConnected){
                        NoNetBar.setVisibility(View.VISIBLE);
                    } else if (!isConnected){
                        NoNetBar.setVisibility(View.INVISIBLE);
                    }

                }
            };
            Toast.makeText(SampleActivity.this, "Broadcast Initialized", Toast.LENGTH_SHORT).show();


            Toast.makeText(SampleActivity.this, "App is Created", Toast.LENGTH_SHORT).show();
        }

        @Override
        protected void onPause() {
            super.onPause();
            Toast.makeText(SampleActivity.this, "App has Paused", Toast.LENGTH_SHORT).show();

            // Unregister your receiver
            unregisterReceiver(breceiver);
            Toast.makeText(SampleActivity.this, "Broadcast UnRegistered", Toast.LENGTH_SHORT).show();
        }
}

此类扩展了AppCompatActivity（像往常一样）。您可以使用此类创建活动，只要您希望接收器处理一些例外情况。

在以下其他活动中使用此课程：

public class MainActivity extends SampleActivity {

    Button btnNext;
    RelativeLayout Network_disconnection;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // Make sure that you can setRelative before calling super.onCreate or you will get a NULL POINTER EXCEPTION
        setRelative(Network_disconnection);

        Toast.makeText(MainActivity.this, "Now Calling Supper", Toast.LENGTH_SHORT).show();
        super.onCreate(savedInstanceState);

    }
}

您可以查看此链接以了解活动生命周期：
https://developer.android.com/training/basics/activity-lifecycle/starting.html 或者如果赶时间，请检查此图片：

检查所有活动的互联网并显示消息WHILE net已断开连接

AIM