android 判断是否有可用网络

 public boolean CheckNetwork() {
		    
		    boolean flag = false;
		    ConnectivityManager cwjManager = (ConnectivityManager) AndroidBaseActivity.self.getSystemService(Context.CONNECTIVITY_SERVICE);
		    if (cwjManager.getActiveNetworkInfo() != null)
		        flag = cwjManager.getActiveNetworkInfo().isAvailable();
		    if (!flag) {
		        Builder b = new AlertDialog.Builder( AndroidBaseActivity.self).setTitle("没有可用的网络").setMessage( AndroidBaseActivity.self.getResources().getString(R.string.net_work_message));
		        b.setPositiveButton("确定", new DialogInterface.OnClickListener() {
		            public void onClick(DialogInterface dialog, int whichButton) {
		                Intent mIntent = new Intent("/");
		                ComponentName comp = new ComponentName("com.android.settings", "com.android.settings.WirelessSettings");
		                mIntent.setComponent(comp);
		                mIntent.setAction("android.intent.action.VIEW");
		                AndroidBaseActivity.self.startActivity(mIntent);
		            }
		        }).setNeutralButton("取消", new DialogInterface.OnClickListener() {
		            public void onClick(DialogInterface dialog, int whichButton) {
		                dialog.cancel();
		            }
		        }).create();
		        b.show();
		    }
		    Toast.makeText(AndroidBaseActivity.self, "test", 1).show();
		   return flag;
		}