java - 在 Android 中创建用于检查互联网连接的对话框

Question

我正在实现在互联网离线时显示对话框，当我运行我的应用程序时，当我单击按钮并且应用程序崩溃时，我收到“FATAL Exception main”和 ClassCastException 。有人可以告诉我我做错了什么吗？感谢您在高级版中的表现。

这是我如何检查是否启用互联网的代码:

public class AndroidDetectInternetConnectionActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        Button btnStatus = (Button) findViewById(R.id.btn_check);

        btnStatus.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {


                if (!isOnline())
                {
                    showNoConnectionDialog(this);

                }
            }

        });

    }

    public static void showNoConnectionDialog(OnClickListener onClickListener) 
    {
        final Context ctx = (Context) onClickListener;
        AlertDialog.Builder builder = new AlertDialog.Builder(ctx);
        builder.setCancelable(true);
        builder.setMessage(R.string.no_connection);
        builder.setTitle(R.string.no_connection_title);
        builder.setPositiveButton(R.string.settings_button_text, new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) 
            {

                ctx.startActivity(new Intent(Settings.ACTION_WIRELESS_SETTINGS));
            }
        });

        builder.setNegativeButton(R.string.cancel_button_text, new DialogInterface.OnClickListener() 
        {
            public void onClick(DialogInterface dialog, int which) 
            {
                return;
            }
        });

        builder.setOnCancelListener(new DialogInterface.OnCancelListener() 
        {
            public void onCancel(DialogInterface dialog) {
                return;
            }
        });

        builder.show();
    }

    public boolean isOnline() 
    {
        ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo netInfo = cm.getActiveNetworkInfo();
        if (netInfo != null && netInfo.isConnectedOrConnecting()) 
        {
            return true;
        }
        return false;
    }

}

//这是我的 Log Cat 堆栈跟踪

11-15 11:57:19.115: D/AndroidRuntime(453): Shutting down VM
11-15 11:57:19.115: W/dalvikvm(453): threadid=1: thread exiting with uncaught exception (group=0x40015560)
11-15 11:57:19.122: E/AndroidRuntime(453): FATAL EXCEPTION: main
11-15 11:57:19.122: E/AndroidRuntime(453): java.lang.ClassCastException: com.example.detectinternetconnection.AndroidDetectInternetConnectionActivity$1
11-15 11:57:19.122: E/AndroidRuntime(453):  at com.example.detectinternetconnection.AndroidDetectInternetConnectionActivity.showNoConnectionDialog(AndroidDetectInternetConnectionActivity.java:99)
11-15 11:57:19.122: E/AndroidRuntime(453):  at com.example.detectinternetconnection.AndroidDetectInternetConnectionActivity$1.onClick(AndroidDetectInternetConnectionActivity.java:64)
11-15 11:57:19.122: E/AndroidRuntime(453):  at android.view.View.performClick(View.java:2485)
11-15 11:57:19.122: E/AndroidRuntime(453):  at android.view.View$PerformClick.run(View.java:9080)
11-15 11:57:19.122: E/AndroidRuntime(453):  at android.os.Handler.handleCallback(Handler.java:587)
11-15 11:57:19.122: E/AndroidRuntime(453):  at android.os.Handler.dispatchMessage(Handler.java:92)
11-15 11:57:19.122: E/AndroidRuntime(453):  at android.os.Looper.loop(Looper.java:123)
11-15 11:57:19.122: E/AndroidRuntime(453):  at android.app.ActivityThread.main(ActivityThread.java:3683)
11-15 11:57:19.122: E/AndroidRuntime(453):  at java.lang.reflect.Method.invokeNative(Native Method)
11-15 11:57:19.122: E/AndroidRuntime(453):  at java.lang.reflect.Method.invoke(Method.java:507)
11-15 11:57:19.122: E/AndroidRuntime(453):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
11-15 11:57:19.122: E/AndroidRuntime(453):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
11-15 11:57:19.122: E/AndroidRuntime(453):  at dalvik.system.NativeStart.main(Native Method)
11-15 11:57:24.892: I/Process(453): Sending signal. PID: 453 SIG: 9

Answer 1

更改此行

 final Context ctx = (Context) onClickListener;

到下面一个

 final Context ctx = AndroidDetectInternetConnectionActivity.this;

基本上，您正在尝试将 onClickListener 转换为 Contex，这是不正确的并且无法转换。要么在需要上下文实例的地方直接使用 ActivityName.this，要么定义 static Context ctx 作为类变量并在 onCreate()< 中初始化它只需添加此行 ctx =this 并记住在使用它之前先对其进行初始化。

享受