android - 强制 Cloce - 致命异常 main java.lang.nullpointerexception

Question

我制作了一个 ListView ，显示数据库中的详细信息。我这里用的是mysql。该应用程序根本不构建，当我调试应用程序时它会强制关闭。这是日志猫:

    12-14 06:15:41.976: E/AndroidRuntime(856): FATAL EXCEPTION: main
12-14 06:15:41.976: E/AndroidRuntime(856): java.lang.NullPointerException
12-14 06:15:41.976: E/AndroidRuntime(856):  at com.example.logreg.customer.model.MainActivity.populateListView(MainActivity.java:183)
12-14 06:15:41.976: E/AndroidRuntime(856):  at com.example.logreg.customer.model.MainActivity.access$6(MainActivity.java:181)
12-14 06:15:41.976: E/AndroidRuntime(856):  at com.example.logreg.customer.model.MainActivity$MainActivityAsync$1.run(MainActivity.java:252)
12-14 06:15:41.976: E/AndroidRuntime(856):  at android.app.Activity.runOnUiThread(Activity.java:4644)
12-14 06:15:41.976: E/AndroidRuntime(856):  at com.example.logreg.customer.model.MainActivity$MainActivityAsync.onPostExecute(MainActivity.java:249)
12-14 06:15:41.976: E/AndroidRuntime(856):  at com.example.logreg.customer.model.MainActivity$MainActivityAsync.onPostExecute(MainActivity.java:1)
12-14 06:15:41.976: E/AndroidRuntime(856):  at android.os.AsyncTask.finish(AsyncTask.java:631)
12-14 06:15:41.976: E/AndroidRuntime(856):  at android.os.AsyncTask.access$600(AsyncTask.java:177)
12-14 06:15:41.976: E/AndroidRuntime(856):  at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
12-14 06:15:41.976: E/AndroidRuntime(856):  at android.os.Handler.dispatchMessage(Handler.java:99)
12-14 06:15:41.976: E/AndroidRuntime(856):  at android.os.Looper.loop(Looper.java:137)
12-14 06:15:41.976: E/AndroidRuntime(856):  at android.app.ActivityThread.main(ActivityThread.java:5041)
12-14 06:15:41.976: E/AndroidRuntime(856):  at java.lang.reflect.Method.invokeNative(Native Method)
12-14 06:15:41.976: E/AndroidRuntime(856):  at java.lang.reflect.Method.invoke(Method.java:511)
12-14 06:15:41.976: E/AndroidRuntime(856):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
12-14 06:15:41.976: E/AndroidRuntime(856):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
12-14 06:15:41.976: E/AndroidRuntime(856):  at dalvik.system.NativeStart.main(Native Method)

这是主要 Activity :

private class MainActivityAsync extends AsyncTask<String, Void, String>{

        @Override
        protected void onPreExecute() {
            progressDialog = new ProgressDialog(MainActivity.this);
            progressDialog.setMessage("retrieving...");
            progressDialog.setIndeterminate(false);
            progressDialog.setCancelable(false);
            progressDialog.show();
        }

        @Override
        protected String doInBackground(String... params) {
            if(params[0] == "delete"){
                serverRequest.sendGetRequest(ServerRequest.urlDelete+"?kode_cust="+selectedList.getKodeCust().toString());
            }else{
                /** Mengirimkan request ke server dan memproses JSON response */ 
                String response = serverRequest.sendGetRequest(ServerRequest.urlSelectAll);
                list = processResponse(response);
            }
            return null;
        }

        @Override
        protected void onPostExecute(String result) {
            progressDialog.dismiss();
            runOnUiThread(new Runnable() {              
                @Override
                public void run() {
                    populateListView();
                }
            });
        }

    }

这是填充 View :

private void populateListView(){
        adapter = new ListAdapter(getApplicationContext(), list);
        listView.setAdapter(adapter);
        listView.setOnItemLongClickListener(new OnItemLongClickListener() {

            @Override
            public boolean onItemLongClick(AdapterView<?> adapterView, View v, int pos, long id) {
                if(actionMode != null){
                    return false;
                }
                actionMode = startActionMode(amCallback);
                v.setSelected(true);
                selectedList = (Customer) adapter.getItem(pos);
                return true;
            }

        });


        listView.setOnItemClickListener(new OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> adapterView, View v, int pos,
                    long id) {
                selectedList = (Customer) adapter.getItem(pos);
                Intent in = new Intent(getApplicationContext(), DetailCustomer.class);
                in.putExtra("kode_cust", selectedList.getKodeCust().toString());
                in.putExtra("nama_cust", selectedList.getNamaCust());
                in.putExtra("contact_person_cust", selectedList.getContactPerson());
                in.putExtra("alm_cust", selectedList.getAlmtCust());
                in.putExtra("wilayah_cust", selectedList.getWilCust());
                in.putExtra("telp_cust", selectedList.getTelpCust());
                in.putExtra("hp_cust", selectedList.getHpCust());
                in.putExtra("fax_cust", selectedList.getFaxCust());
                in.putExtra("email_cust", selectedList.getEmailCust());
                in.putExtra("limit_cust", selectedList.getLimitCust().toString());

                startActivity(in);
            }
        });
       }

我的populateview代码有问题还是有代码我没有输入？因为一开始它可以工作，但是当我在eclipse中的新项目android中制作它后，它显示了上面的问题。

Answer 1

您的代码可以在该方法中抛出空指针异常的唯一方法以及堆栈跟踪，是在调用该方法时 listView 是否为 null。您需要查看初始化 listView 的方式和位置。

该方法的其他部分可能会引发此类异常，但它们位于内部类内部，如果在那里引发异常，那么这些方法将显示在堆栈跟踪中。