Android AsyncTast onPostExecute不更新UI元素：引发NullPointerException

我一度陷入这个问题。 这是我的密码

public class PilgrimFriendActivity extends Activity {

    private String DOMAIN = "http://";

    private String LAWS_URL = "";
    private String LOCATIONS_URL = "";

    private ListView list;
    private TextView content;
    private Law law  ;
    private Location location;
    private ProgressDialog dialog;
    private SharedPreferences preferences;


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

        preferences = getSharedPreferences("com.hackontech.pilgrim_preferences", MODE_PRIVATE);
        this.DOMAIN += preferences.getString("DOMAIN","192.168.0.104");
        this.LAWS_URL = DOMAIN + "/pilgrimfriend/main/getAllLaws";
        this.LOCATIONS_URL = DOMAIN + "/pilgrimfriend/main/getAllLocations";

        dialog = new ProgressDialog(this);
        content = (TextView) findViewById(R.id.content);
        list = (ListView) findViewById(R.id.laws);
        this.lLaws();

    }


    public void lLaws() {

        final class RequestTask extends AsyncTask<String, String, String>{

            private String URL = null;

            @Override
            protected String doInBackground(String... uri) {
                String result = null;
                URL = uri[0];
                try {

                    //Create default http client
                    HttpClient httpclient = new DefaultHttpClient();
                    HttpGet httpget = new HttpGet(URL);
                    Log.v("URL",URL);
                    HttpResponse response = httpclient.execute(httpget);
                    //Retrieve the response body or "entity"
                    HttpEntity entity = response.getEntity();
                    //Return the entity as String
                    result = EntityUtils.toString(entity);
                    Log.v("result",result.toString());

                } catch (Exception e) {
                    return e.getMessage();
                }

                return result;
            }

            @Override
            protected void onPostExecute(String result) {
                //super.onPostExecute(result);
                dialog.dismiss();
                try{

                    JSONArray jArray = new JSONArray(result);

                    JSONObject json_data;
                    ArrayList<String> items = new ArrayList<String>();
                    for(int i=0; i < jArray.length() ; i++) {
                        json_data = jArray.getJSONObject(i);
                        int id=json_data.getInt("id");
                        String title=json_data.getString("title");
                        String scholor =json_data.getString("scholor");
                        items.add(title+" ("+scholor+")");
                    }

                    content.setText(result);
                    ArrayAdapter<String> mArrayAdapter = new ArrayAdapter<String>(getApplicationContext(),  
                            android.R.layout.simple_list_item_1, items);
                    list.setAdapter(mArrayAdapter);

                    Toast.makeText(getApplicationContext(), result, Toast.LENGTH_LONG).show();

                }
                catch(JSONException e) {
                    //content.setText(e.getMessage());
                }
                //Do anything with response..
            }

            @Override
            protected void onPreExecute() {
                // TODO Auto-generated method stub
                super.onPreExecute();

                dialog.setTitle("Downloading Laws Data");
                dialog.show();
            }

        }

        new RequestTask().execute(LAWS_URL);
    }

---

由于某种原因，

onPostExecute

方法在方法完成后立即执行所有UI更新

例如：

@Override
protected Void doInBackground() {
    someTextView.setText("Do In Background Finished!");
}

@Override
protected void onPostExecute () {
    someTextView.setText("Post Execute Started");
    try {
        Thread.sleep(5000);
    } catch (InterruptedException e) {
        // ..
    }
    someTextView.setText("Post Execute Finished");
}

---

将导致显示“后台执行完成！”并在5秒后（当

onPostExecute

结束时）将用“Post Execute Started”更新文本，并立即用“Post Execute Finished”再次更新文本。我猜

内容

为空。你初始化它了吗？是的，我可以在其他任何地方更新它，不仅内容，listview也不工作，简言之，它没有更新UI，但奇怪的是进程对话框正在显示，Toast确实显示添加

崩溃日志

和行号<代码>对话框显示还是取消？对话框取消，让我发布完成code@user868900日志中的异常回溯告诉您引发异常的确切行号，为什么不简单地检查那里发生了什么？在那里放置一个断点并在调试器控制下运行应用程序怎么样？这些都是基本的东西。

@Override
protected Void doInBackground() {
    someTextView.setText("Do In Background Finished!");
}

@Override
protected void onPostExecute () {
    someTextView.setText("Post Execute Started");
    try {
        Thread.sleep(5000);
    } catch (InterruptedException e) {
        // ..
    }
    someTextView.setText("Post Execute Finished");
}