无法更改另一个活动中设置的int值

Question

我正在尝试通过单击警报活动中的ImageButton将计数器设置为0，计数器位于Server.java类（这是 TCP服务器）中，但是当我正在尝试通过设置 alert.java ：

来更改值

Server server;
    refreshing.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            server.count = 0;
            SharedPreferences prefs = getSharedPreferences("MY_DATA", MODE_PRIVATE);
            SharedPreferences.Editor editor = prefs.edit();
            editor.clear();
            editor.apply();
            Intent intent = getIntent();
            overridePendingTransition(0, 0);
            intent.addFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION);
            finish();
            overridePendingTransition(0, 0);
            startActivity(intent);
        }
    });

崩溃时出错：

Java.lang.NullPointerException: Attempt to write to field 'int com.example.sguidetti.selfmanegment.Server.count' on a null object reference

我在主要活动中使用相同的操作来重置同一个计数器，方法是点击另一个ImageButton，这样可行。

（Ps：我是android的新手，所以我无法理解很多东西）

编辑这里是Server.java

public class Server {
DataBaseHandler myDB;
allert Allert;
MainActivity activity;
RecyclerViewAdapter adapterView;
Adapter adapter;
ServerSocket serverSocket;
public static int count=0;
String letto = "";
private SharedPreferences prefs;
static final int socketServerPORT = 8080;

public Server(MainActivity activity) {
    this.activity = activity;
    Thread socketServerThread = new Thread(new SocketServerThread());
    socketServerThread.start();
}

public int getPort() {
    return socketServerPORT;
}


public void onDestroy() {
    if (serverSocket != null) try {
        serverSocket.close();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}


private class SocketServerThread extends Thread {
    Vibrator vibrator;
    String date,ora;
    long[] pattern = {0, 1000, 500, 1000, 500, 1000};

    int lun;

    @Override
    public void run() {
        InputStream leggi;
        try {


            serverSocket = new ServerSocket(socketServerPORT);

            while (true) {
                myDB = DataBaseHandler.getInstance(activity);

                Socket socket = serverSocket.accept();
                leggi = socket.getInputStream();
                byte[] data = new byte[1000];
                lun = leggi.read(data, 0, data.length);
                letto = new String(data, "UTF-8");
                count++;
                MediaPlayer mPlay = MediaPlayer.create(activity, R.raw.gabsuono);
                mPlay.start();

                vibrator = (Vibrator) activity.getSystemService(VIBRATOR_SERVICE);
                vibrator.vibrate(pattern, -1);

                date = new SimpleDateFormat("dd-MM-yyyy").format(new Date());
                ora = new SimpleDateFormat("HH:mm:ss").format(new Date());
                myDB.insertDataServer(date, ora, letto);


                //adapterView.notifyDataSetChanged();

                activity.runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        prefs = activity.getSharedPreferences("MY_DATA", MODE_PRIVATE);
                        SharedPreferences.Editor edit = prefs.edit();
                        edit.putInt("counter", count);
                        edit.commit();
                        activity.msg.setText(String.valueOf(count));
                        activity.msg.setVisibility(View.VISIBLE);

                    }
                });
                leggi.close();


            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();

        }

    }


}

public void Parti() {
    prefs = activity.getSharedPreferences("MY_DATA", MODE_PRIVATE);
    count = prefs.getInt("counter", count);
    activity.msg.setText("" + count);
    if (count == 0)
        activity.msg.setVisibility(View.INVISIBLE);
    else
        activity.msg.setVisibility(View.VISIBLE);


}

}

Answer 1

你需要使用int static

public static final int count = 0;

然后您可以从其他活动中访问该值

Server.count = 5;

<强>更新

在服务器中声明您的计数

public static final String COUNT = "count";

也宣布

public static final String PREFS = "prefs";

并声明你的共享prefes

 SharedPreferences prefs = getSharedPreferences(Server.PREFS, MODE_PRIVATE);
 SharedPreferences.Editor editor = prefs.edit();

然后在您调用sharedPreference

之后单击按钮

editor.putInt(Server.COUNT,5).commit();

然后

获取警报活动中的int值，如下所示

int count = prefs.getInt(Server.COUNT,0);

Answer 2

您忘记初始化server对象，添加：

Server server = new Server();