Android：檢查網絡連接狀態

（1）在AndroidManifest.xml文件中添加必要的權限。

訪問網絡我們需要 INTERNET 權限
檢查網絡狀態我們需要 ACCESS_NETWORK_STATE 權限

1. <!-- Internet Permissions -->
2. <uses-permission android:name="android.permission.INTERNET" />
4. <!-- Network State Permissions -->
5. <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

（2）創建工具類ConnectionDetector.java

1. import android.content.Context;
2. import android.net.ConnectivityManager;
3. import android.net.NetworkInfo;
5. public class ConnectionDetector {
7. private Context _context;
9. public ConnectionDetector(Context context){
10. this._context = context;
11. }
12. /**
13. * 判斷網絡是否連接
14. * @return true/false
15. */
16. public boolean isConnectingToInternet(){
17. ConnectivityManager connectivity = (ConnectivityManager) _context.getSystemService(Context.CONNECTIVITY_SERVICE);
18. if (connectivity != null)
19. {
20. NetworkInfo[] info = connectivity.getAllNetworkInfo();
21. if (info != null) {
22. for (int i = 0; i < info.length; i++) {
23. if (info[i].getState() == NetworkInfo.State.CONNECTED) {
24. return true;
25. }
26. }
27. }
28. }
29. return false;
30. }
31. }

（3）上面工具類的使用：當需要在你的應用中檢查網絡狀態時調用isConnectingToInternet()函數，返回true或false。

1. ConnectionDetector cd = new ConnectionDetector(getApplicationContext());
2. Boolean isInternetPresent = cd.isConnectingToInternet(); // true or false

（4）下面是一個小測試，實現單擊按鈕，彈出alert dialog顯示網絡連接狀態。

在res/layout/main.xml中創建一個按鈕

1. <?xml version="1.0" encoding="utf-8"?>
2. <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
3. android:layout_width="fill_parent"
4. android:layout_height="fill_parent"
5. android:orientation="vertical" >
7. <TextView
8. android:layout_width="fill_parent"
9. android:layout_height="wrap_content"
10. android:text="Detect Internet Status" />
12. <Button android:id="@+id/btn_check"
13. android:layout_height="wrap_content"
14. android:layout_width="wrap_content"
15. android:text="Check Internet Status"
16. android:layout_centerInParent="true"/>
18. </RelativeLayout>

MainActivity.java

1. import android.app.Activity;
2. import android.app.AlertDialog;
3. import android.content.Context;
4. import android.content.DialogInterface;
5. import android.os.Bundle;
6. import android.view.View;
7. import android.widget.Button;
9. public class AndroidDetectInternetConnectionActivity extends Activity {
11. // flag for Internet connection status
12. Boolean isInternetPresent = false;
14. // Connection detector class
15. ConnectionDetector cd;
17. @Override
18. public void onCreate(Bundle savedInstanceState) {
19. super.onCreate(savedInstanceState);
20. setContentView(R.layout.main);
22. Button btnStatus = (Button) findViewById(R.id.btn_check);
24. // creating connection detector class instance
25. cd = new ConnectionDetector(getApplicationContext());
27. /**
28. * Check Internet status button click event
29. */
30. btnStatus.setOnClickListener(new View.OnClickListener() {
32. @Override
33. public void onClick(View v) {
35. // get Internet status
36. isInternetPresent = cd.isConnectingToInternet();
38. // check for Internet status
39. if (isInternetPresent) {
40. // Internet Connection is Present
41. // make HTTP requests
42. showAlertDialog(AndroidDetectInternetConnectionActivity.this, "Internet Connection",
43. "You have internet connection", true);
44. } else {
45. // Internet connection is not present
46. // Ask user to connect to Internet
47. showAlertDialog(AndroidDetectInternetConnectionActivity.this, "No Internet Connection",
48. "You don't have internet connection.", false);
49. }
50. }
51. });
52. }
54. /**
55. * Function to display simple Alert Dialog
56. * @param context - application context
57. * @param title - alert dialog title
58. * @param message - alert message
59. * @param status - success/failure (used to set icon)
60. * */
61. public void showAlertDialog(Context context, String title, String message, Boolean status) {
62. AlertDialog alertDialog = new AlertDialog.Builder(context).create();
64. // Setting Dialog Title
65. alertDialog.setTitle(title);
67. // Setting Dialog Message
68. alertDialog.setMessage(message);
70. // Setting alert dialog icon
71. alertDialog.setIcon((status) ? R.drawable.success : R.drawable.fail);
73. // Setting OK Button
74. alertDialog.setButton("OK", new DialogInterface.OnClickListener() {
75. public void onClick(DialogInterface dialog, int which) {
76. }
77. });
79. // Showing Alert Message
80. alertDialog.show();
81. }
82. }

（5）測試結果

Internet Connection

No Internet Connection