Question

我在Retriver.java类中调用MainActivity函数sendToServer（arguments），当我在mainactivity类中工作时，此函数正常工作。但是当我从retriver.java调用它时，我得到nullPointExceltion

logcat的：

12-29 02:24:07.772: E/AndroidRuntime(12958): FATAL EXCEPTION: main
12-29 02:24:07.772: E/AndroidRuntime(12958): Process: com.example.osc, PID: 12958
12-29 02:24:07.772: E/AndroidRuntime(12958): java.lang.NullPointerException
12-29 02:24:07.772: E/AndroidRuntime(12958):    at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:109)
12-29 02:24:07.772: E/AndroidRuntime(12958):    at com.example.osc.MainActivity$AsyncCreateUser.onPostExecute(MainActivity.java:340)
12-29 02:24:07.772: E/AndroidRuntime(12958):    at com.example.osc.MainActivity$AsyncCreateUser.onPostExecute(MainActivity.java:1)
12-29 02:24:07.772: E/AndroidRuntime(12958):    at android.os.AsyncTask.finish(AsyncTask.java:632)
12-29 02:24:07.772: E/AndroidRuntime(12958):    at android.os.AsyncTask.access$600(AsyncTask.java:177)
12-29 02:24:07.772: E/AndroidRuntime(12958):    at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
12-29 02:24:07.772: E/AndroidRuntime(12958):    at android.os.Handler.dispatchMessage(Handler.java:102)
12-29 02:24:07.772: E/AndroidRuntime(12958):    at android.os.Looper.loop(Looper.java:136)
12-29 02:24:07.772: E/AndroidRuntime(12958):    at android.app.ActivityThread.main(ActivityThread.java:5017)
12-29 02:24:07.772: E/AndroidRuntime(12958):    at java.lang.reflect.Method.invokeNative(Native Method)
12-29 02:24:07.772: E/AndroidRuntime(12958):    at java.lang.reflect.Method.invoke(Method.java:515)
12-29 02:24:07.772: E/AndroidRuntime(12958):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
12-29 02:24:07.772: E/AndroidRuntime(12958):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
12-29 02:24:07.772: E/AndroidRuntime(12958):    at dalvik.system.NativeStart.main(Native Method)

当我将getApplicationContext（）更改为MainActivity.this时，它仍然会出错并且logcat reslut就是这个。

12-29 02:43:09.829: E/AndroidRuntime(20558): FATAL EXCEPTION: main
12-29 02:43:09.829: E/AndroidRuntime(20558): Process: com.example.osc, PID: 20558
12-29 02:43:09.829: E/AndroidRuntime(20558): java.lang.NullPointerException
12-29 02:43:09.829: E/AndroidRuntime(20558):    at android.content.ContextWrapper.getResources(ContextWrapper.java:89)
12-29 02:43:09.829: E/AndroidRuntime(20558):    at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:78)
12-29 02:43:09.829: E/AndroidRuntime(20558):    at android.widget.Toast.<init>(Toast.java:93)
12-29 02:43:09.829: E/AndroidRuntime(20558):    at android.widget.Toast.makeText(Toast.java:241)
12-29 02:43:09.829: E/AndroidRuntime(20558):    at com.example.osc.MainActivity$AsyncCreateUser.onPostExecute(MainActivity.java:340)
12-29 02:43:09.829: E/AndroidRuntime(20558):    at com.example.osc.MainActivity$AsyncCreateUser.onPostExecute(MainActivity.java:1)
12-29 02:43:09.829: E/AndroidRuntime(20558):    at android.os.AsyncTask.finish(AsyncTask.java:632)
12-29 02:43:09.829: E/AndroidRuntime(20558):    at android.os.AsyncTask.access$600(AsyncTask.java:177)
12-29 02:43:09.829: E/AndroidRuntime(20558):    at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
12-29 02:43:09.829: E/AndroidRuntime(20558):    at android.os.Handler.dispatchMessage(Handler.java:102)
12-29 02:43:09.829: E/AndroidRuntime(20558):    at android.os.Looper.loop(Looper.java:136)
12-29 02:43:09.829: E/AndroidRuntime(20558):    at android.app.ActivityThread.main(ActivityThread.java:5017)
12-29 02:43:09.829: E/AndroidRuntime(20558):    at java.lang.reflect.Method.invokeNative(Native Method)
12-29 02:43:09.829: E/AndroidRuntime(20558):    at java.lang.reflect.Method.invoke(Method.java:515)
12-29 02:43:09.829: E/AndroidRuntime(20558):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
12-29 02:43:09.829: E/AndroidRuntime(20558):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
12-29 02:43:09.829: E/AndroidRuntime(20558):    at dalvik.system.NativeStart.main(Native Method)

在Retriver.java中

 if (c.moveToFirst()) {
             sender_name = c.getString(c.getColumnIndexOrThrow("Chidname"));
             //sender_name = c.getString(c.getColumnIndex("senderName"));
             MainActivity obj = new MainActivity();
             if(
             obj.sendToServer(c.getString(c.getColumnIndexOrThrow("Chidname")),
                     c.getString(c.getColumnIndexOrThrow("Chidname")),
                     c.getString(c.getColumnIndexOrThrow("ChildAge")),
                     c.getString(c.getColumnIndexOrThrow("ChildGender")),
                     c.getString(c.getColumnIndexOrThrow("ChildAddress")),
                     c.getString(c.getColumnIndexOrThrow("Sendername")),
                     c.getString(c.getColumnIndexOrThrow("SenderEmail")),
                     c.getString(c.getColumnIndexOrThrow("SenderSimNo")),
                     c.getString(c.getColumnIndexOrThrow("SenderContact")),
                     c.getString(c.getColumnIndexOrThrow("Longitude")),
                     c.getString(c.getColumnIndexOrThrow("Latitude")),
                     "get this later")){
                 String deleteRecored = "DELETE FROM tblOSC WHERE _Id="+c.getString(c.getColumnIndexOrThrow("_Id"));
                 db.execSQL(deleteRecored);
             }
         }

         c.close();

MainActivity.java

public boolean sendToServer(String cpp, String cn,String ca,String cg, String cadd,String sn,String se,
        String ssn, String sp, String log, String lat, String cpis) {
    UserDetailsTable userDetail = new UserDetailsTable(cpp,
            cn, ca,
            cg,
            cadd, sn, se,
            sn, sp, log,
            lat, cpis);
    new AsyncCreateUser().execute(userDetail);
    return SENT_TO_SERVER_FLAG;
}

protected class AsyncCreateUser extends
        AsyncTask<UserDetailsTable, Void, Void> {

    @Override
    protected Void doInBackground(UserDetailsTable... params) {

        RestAPI api = new RestAPI();
        try {

            api.CreateNewAccount(params[0].getchildPhotoPath(),
                    params[0].getchildName(), params[0].getchildAge(),
                    params[0].getchildGender(),
                    params[0].getchildAddress(), params[0].getsenderName(),
                    params[0].getsenderCellPhone(),
                    params[0].getsenderMobile(),
                    params[0].getsenderEmail(), params[0].getlongitude(),
                    params[0].getlattitude(),
                    params[0].childPhotoImageString);

        } catch (Exception e) {
            // TODO Auto-generated catch block
            Log.d("AsyncCreateUser", e.getMessage());

        }
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {

        SENT_TO_SERVER_FLAG = true;
        Toast.makeText(getApplicationContext(),"sent to PEF", Toast.LENGTH_LONG).show();
    }

}

Answer 1

使用 - MainActivity.this代替getApplicationContext();

@Override
    protected void onPostExecute(Void result) {

        SENT_TO_SERVER_FLAG = true;
        Toast.makeText(MainActivity.this,"sent to PEF", Toast.LENGTH_LONG).show();
    }

Answer 2

在MainActivity定义中定义一个全局Context contex变量（即在onCreate（）开始之前），并在onCreate中为其赋予contex = getApplicationContext()。

然后使用contex作为Toast参数。

Toast.makeText(contex, "sent to PEF", ...

Async onPostExecute中的NullPointerException

2 个答案: