Java OpenFileOutput（）获取nullPointerException

我创建了一个静态处理程序，用于从侦听传入蓝牙数据的线程接收数据。 此处理程序调用：measure_finish2（），此方法调用名为：measure_finish（）的非静态metod，在最后一个处理程序中，我需要调用openFileOutput方法，但我有一个nullPointerException，即使在调用简单Toast时，我也有相同的nullPointerException，这是我代码的一部分：

    public class MainActivity Extends Activity{
    ...
    public void sending_tubes_to_clean(){
        stream_cleaning_tubes = "15";
        for(int i = 0;i<4;i++){
            if(itemsChecked[i] == true){
                stream_cleaning_tubes += "," + Integer.toString(i+1);
            }
        }
        if(conectToServerThread != null){
            conectToServerThread.commsThread.write(stream_cleaning_tubes);
            Toast.makeText(getBaseContext(), "Cleaning the selected Tubes!", Toast.LENGTH_SHORT).show();
            cleaning_status();
        }else{
            Toast.makeText(getBaseContext(), "You must be connected to the Viscometer!...", Toast.LENGTH_SHORT).show();
        }
        Log.d(tag,stream_cleaning_tubes);
    }        
public static Handler MainReceiver = new Handler(){
            @Override
            public void handleMessage(Message msg){
                int numOfBytesReceived = msg.arg1;
                byte[] buffer = (byte[]) msg.obj;
                String strReceived = new String(buffer);
                String comand;
                strReceived = strReceived.substring(3,numOfBytesReceived);
                comand = strReceived.substring(0,2);

                if(comand.toString().equals("03")){
                    //MainActivity o = new MainActivity();
                    measure_finish2(strReceived.substring(3));
                    //measure_finish2(strReceived.substring(3));
                }

            }
        };
        public static String get_data(String aux){
            String aux2 = null;
            aux2 = aux.substring(0,aux.indexOf(","));
            return aux2;
        }

        public static void measure_finish2(String data){
            MainActivity o = new MainActivity();
            o.measure_finish(data);
        }
        public void measure_finish(String data){
            String data_to_save,strdate,tube,temp,time,cte_tube,visco;
            String file_name = "results.txt";
            Calendar c = Calendar.getInstance();
            SimpleDateFormat sdf = new SimpleDateFormat("dd-MM-yyyy HH:mm");
            strdate = sdf.format(c.getTime());
            tube = get_data(data);
            data = data.substring(data.indexOf(",")+1);
            temp = get_data(data);
            data = data.substring(data.indexOf(",")+1);
            time = get_data(data);
            data = data.substring(data.indexOf(",")+1);
            cte_tube = get_data(data);
            data = data.substring(data.indexOf(",")+1);
            visco = get_data(data);
            data_to_save = sample_id_var + user_id_var + strdate + "Tube# " + tube + temp + "°C"+ cte_tube + time + "s" + visco + "cSt" + "\n";
            try{
                FileOutputStream fos = openFileOutput(file_name,MODE_WORLD_READABLE);
                OutputStreamWriter osw = new OutputStreamWriter(fos);
                try {
                    osw.write(data_to_save);
                    osw.flush();
                    osw.close();
                }catch (IOException e) {
                    e.printStackTrace();
                }

            //Toast.makeText(getBaseContext(), "F saved", Toast.LENGTH_SHORT).show();
                }catch(FileNotFoundException e)
                {
                    e.printStackTrace();
                }

            samp_id_view.setText(data_to_save);
            cleaning_status();
        }

首先，永远不要自己创建

活动的实例。Android的框架创造了这些，而不是你。此
o
未正确初始化，因此任何使用它的尝试，例如
openFileOutput（）
、一个
Toast
等，通常都会崩溃

其次，不要在主应用程序线程上执行磁盘I/O。
measure_finish（）
中显示的代码应该由蓝牙线程或其他后台线程执行，而不是由主应用程序线程执行。
正如您在日志猫中看到的，您的NullPointerException是由MainActivity引起的。将\u发送到\u clean（MainActivity.java:320）。但是你没有在你展示祝酒词的地方发布代码。是的，但是在这个方法里面只有祝酒词：我已经更新了我的帖子，看看它们，如果有人现在知道如何解决这个问题，请告诉我……你仍然有被禁止的“新MainActivity”。我们看不到Toast调用的函数。请调整您的代码。这当然是错误的原因。但真正的错误很可能是让这个类扩展活动——它似乎与活动所做的任何事情都没有多大关系。可能应该做的是将有效的上下文或对活动的其他引用传递给它，然后可以使用它来执行诸如显示toast或获取包路径之类的操作。然后使用
new
创建实例是合法的。向构造函数添加一个上下文参数，从触发活动中传递“this”。最好是简单地pas从GetFileDir（）获得的目录，但随后必须跳转一个额外步骤，创建一个文件，将其作为父级，并将指定的文件名作为第二个参数，调用其setReadable（true，false）来设置世界可读权限，然后从它创建一个FileOutputStream.Commonware是正确的，我将我的i/O任务移动到后台线程，并将上下文作为参数传递，现在我的代码工作正常。
 04-17 17:09:18.926: E/AndroidRuntime(1685): FATAL EXCEPTION: main
04-17 17:09:18.926: E/AndroidRuntime(1685): Process: com.callirgos.viscopi, PID: 1685
04-17 17:09:18.926: E/AndroidRuntime(1685): java.lang.IllegalStateException: Could not execute method of the activity
04-17 17:09:18.926: E/AndroidRuntime(1685):     at android.view.View$1.onClick(View.java:4007)
04-17 17:09:18.926: E/AndroidRuntime(1685):     at android.view.View.performClick(View.java:4756)
04-17 17:09:18.926: E/AndroidRuntime(1685):     at android.view.View$PerformClick.run(View.java:19749)
04-17 17:09:18.926: E/AndroidRuntime(1685):     at android.os.Handler.handleCallback(Handler.java:739)
04-17 17:09:18.926: E/AndroidRuntime(1685):     at android.os.Handler.dispatchMessage(Handler.java:95)
04-17 17:09:18.926: E/AndroidRuntime(1685):     at android.os.Looper.loop(Looper.java:135)
04-17 17:09:18.926: E/AndroidRuntime(1685):     at android.app.ActivityThread.main(ActivityThread.java:5221)
04-17 17:09:18.926: E/AndroidRuntime(1685):     at java.lang.reflect.Method.invoke(Native Method)
04-17 17:09:18.926: E/AndroidRuntime(1685):     at java.lang.reflect.Method.invoke(Method.java:372)
04-17 17:09:18.926: E/AndroidRuntime(1685):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
04-17 17:09:18.926: E/AndroidRuntime(1685):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
04-17 17:09:18.926: E/AndroidRuntime(1685): Caused by: java.lang.reflect.InvocationTargetException
04-17 17:09:18.926: E/AndroidRuntime(1685):     at java.lang.reflect.Method.invoke(Native Method)
04-17 17:09:18.926: E/AndroidRuntime(1685):     at java.lang.reflect.Method.invoke(Method.java:372)
04-17 17:09:18.926: E/AndroidRuntime(1685):     at android.view.View$1.onClick(View.java:4002)
04-17 17:09:18.926: E/AndroidRuntime(1685):     ... 10 more
04-17 17:09:18.926: E/AndroidRuntime(1685): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.FileOutputStream android.content.Context.openFileOutput(java.lang.String, int)' on a null object reference
04-17 17:09:18.926: E/AndroidRuntime(1685):     at android.content.ContextWrapper.openFileOutput(ContextWrapper.java:181)
04-17 17:09:18.926: E/AndroidRuntime(1685):     at com.callirgos.viscopi.MainActivity.measure_finish(MainActivity.java:434)
04-17 17:09:18.926: E/AndroidRuntime(1685):     at com.callirgos.viscopi.MainActivity.measure_finish2(MainActivity.java:415)
04-17 17:09:18.926: E/AndroidRuntime(1685):     at com.callirgos.viscopi.MainActivity.test_files(MainActivity.java:478)
04-17 17:09:18.926: E/AndroidRuntime(1685):     ... 13 more

MainActivity o = new MainActivity();