判断手机联网状态

在开发过程中，点击应用跳转到主界面时，对于需要联网才能用的设备而言，需要作出设备是否联网的判断,并且根据是否联网来确定下一步的操作，

如果联网了，则直接从动画进入主界面，否则弹出一个对话框 AlertDialog,来选择是否进入设置界面，进行网络连接操作。下面是一个实例：

布局文件：

<LinearLayout 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"
    tools:context=".MainActivity" >

<ImageView 
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   android:src="@drawable/splash"
android:scaleType="fitXY"
   android:id="@+id/main_iv"/>

</LinearLayout>

anim文件夹下的动画文件:

<?xml version="1.0" encoding="utf-8"?>
<alpha
    android:fromAlpha="0.2"
    android:toAlpha="1.0"
    android:duration="3000"
    android:interpolator="@android:anim/linear_interpolator"
    android:fillAfter="true"
    xmlns:android="http://schemas.android.com/apk/res/android">
</alpha>

主要程序:

public class MainActivity extends Activity {
private ImageView iv;
private AlphaAnimation aa;
private AlertDialog.Builder ab;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
iv = (ImageView) findViewById(R.id.main_iv);
aa = (AlphaAnimation) AnimationUtils.loadAnimation(this, R.anim.alpha_splash);
iv.setAnimation(aa);
aa.setAnimationListener(new AnimationListener() {
@Override
public void onAnimationStart(Animation animation) {
// TODO Auto-generated method stub

}

@Override
public void onAnimationRepeat(Animation animation) {
// TODO Auto-generated method stub


}

@Override
public void onAnimationEnd(Animation animation) {
// TODO Auto-generated method stub
//判断设备是否联网
if(isConnected())//联网状态
{
}
else//非联网状态
{
ab = new Builder(MainActivity.this);
ab.setTitle("提示");
ab.setMessage("没有联网，请去设置");
ab.setPositiveButton("ok", new OnClickListener() {

@Override
public void onClick(DialogInterface dialog, int which) {
// TODO Auto-generated method stub
Intent intent = new Intent(Settings.ACTION_SETTINGS);
startActivity(intent);
}
});
ab.setNegativeButton("cancel", new OnClickListener() {

@Override
public void onClick(DialogInterface dialog, int which) {
// TODO Auto-generated method stub
MainActivity.this.finish();
}
});
ab.create();
ab.show();
}
}
});
}
private boolean isConnected() {//判断是否联网的方法
// TODO Auto-generated method stub
boolean bo =false;
ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo ni = cm.getActiveNetworkInfo();
if(ni==null)
{
bo = false;
}
else
{
bo = ni.isConnected();
}
return bo;
}