按书上所说,按Home键,然后启动和禁用网络,不出现toast
可是按返回键,回到桌面就出现toast,如下图:
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.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Toast;
public class MainActivity extends Activity {
private boolean mReceiverTag=false;
private IntentFilter intentFilter;
private NetworkChangeReceiver networkChangeReceiver;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
intentFilter=new IntentFilter();
intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");
networkChangeReceiver=new NetworkChangeReceiver();
}
@Override
protected void onDestroy()
{
super.onDestroy();
if(!mReceiverTag)
{
mReceiverTag=true;
registerReceiver(networkChangeReceiver,intentFilter);
}
else
{
mReceiverTag=false;
unregisterReceiver(networkChangeReceiver);
}
}
class NetworkChangeReceiver extends BroadcastReceiver
{
@Override
public void onReceive(Context context,Intent intent)
{
Toast.makeText(context, "network changes", Toast.LENGTH_SHORT).show();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
如果是这样的话,这程序哪里是在监听网络变化?