java - 无法从 onPostExecute() 的 doInBackGround() 进程获取值

Question

我正在使用 AsyncTask 从数据库插入、更新和删除数据。我用这段代码来插入、更新、删除，它工作得很好。但是当我想使用 select 并在 EditText 处显示数据时，我无法从 doInBackground() 获取值到 onPostExecute() 并且什么也没显示。

这是我的代码:

MenuUtama.java

public class MenuUtama extends Activity {

    /** Called when the activity is first created. */ 
    private TextView nama_user;
    private String nm_user = "";
    private EditText kode, nama, harga, deskripsi; 
    private Button insert, update, delete, cek; 
    private String kode1, nama1, harga1, deskripsi1; 
    JSONArray data = null;

    @Override
    public void onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.activity_main2);

        kode = (EditText) findViewById(R.id.editKode); 
        nama = (EditText) findViewById(R.id.editNama); 
        harga = (EditText) findViewById(R.id.editHarga); 
        deskripsi = (EditText) findViewById(R.id.editDes); 
        cek = (Button) findViewById(R.id.btnCek);
        insert = (Button) findViewById(R.id.buttonInsert); 
        update = (Button) findViewById(R.id.buttonUpdate); 
        delete = (Button) findViewById(R.id.buttonDelete); 
        nama_user = (TextView) findViewById(R.id.textView3);

        Intent i = getIntent();
        nm_user = i.getStringExtra("nama_user"); 
        nama_user.setText(nm_user);


        insert.setOnClickListener(new OnClickListener() { 

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub 

                String url = "";
                url = "http://192.168.1.10/crudsederhana/aksi.php";

                try {
                    String ko = URLEncoder.encode(kode.getText().toString(),"utf-8");
                    String n = URLEncoder.encode(nama.getText().toString(),"utf-8"); 
                    String hr = URLEncoder.encode(harga.getText().toString(),"utf-8");
                    String d = URLEncoder.encode(deskripsi.getText().toString(), "utf-8");

                    url += "?a=insert&kd=" + ko + "&nm=" + n + "&hrg=" + hr + "&deskripsi=" + d;

                    new CRUD().execute(url);
                }

                catch (UnsupportedEncodingException e) { 
                    e.printStackTrace();
                }
            }
        });

        update.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) { 
                String url = "";

                url = "http://192.168.1.10/crudsederhana/aksi.php";

                try { 
                    String ko = URLEncoder.encode(kode.getText().toString(),"utf-8");
                    String n = URLEncoder.encode(nama.getText().toString(),"utf-8");
                    String hr = URLEncoder.encode(harga.getText().toString(),"utf-8");
                    String d = URLEncoder.encode(deskripsi.getText().toString(), "utf-8");

                    url += "?a=update&kd=" + ko + "&nm=" + n + "&hrg=" +hr+ "&des=" + d;

                    new CRUD().execute(url);
                } 

                catch (UnsupportedEncodingException e) { 
                    e.printStackTrace();
                }
            }
        });

        delete.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub 
                String url = "";
                kode1 = kode.getText().toString(); 
                url = "http://192.168.1.10/crudsederhana/aksi.php?a=delete&kd=" + kode1;

                new CRUD().execute(url);
            }
        });

        cek.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub 
                String url = "";
                kode1 = kode.getText().toString();
                url = "http://192.168.1.10/crudsederhana/aksi.php?a=read&kd="+kode1;

                new CRUD().execute(url);
            }
        });
    }

    public class CRUD extends AsyncTask<String, String, String> { 
        String success;
        String kode_d, nama_d, harga_d, des_d;

        @Override
        protected void onPreExecute() { 
            super.onPreExecute();
        }

        @Override
        protected String doInBackground(String... params) {
            JSONParser jParser = new JSONParser(); 
            JSONObject json = jParser.getJSONFromUrl(params[0]);

            try {
                success = json.getString("success"); 
                Log.e("error", "nilai sukses=" + success); 
                JSONArray hasil = json.getJSONArray("login"); 

                if (success.equals("1")) {
                    for (int i = 0; i < hasil.length(); i++) {
                        JSONObject c = hasil.getJSONObject(i);

                        kode_d = c.getString("kd"); 
                        nama_d = c.getString("nm"); 
                        harga_d = c.getString("hrg"); 
                        des_d = c.getString("deskripsi");
                    }
                }

                else {
                    Log.e("erro", "tidak bisa ambil data 0");
                }
            }

            catch (Exception e) {
                // TODO: handle exception
                Log.e("erro", "tidak bisa ambil data 1");
            }

            return kode_d;
        }

        protected void onPostExecute(String result) {
            super.onPostExecute(result);

            kode.setText(kode_d); 
            nama.setText(nama_d); 
            harga.setText(harga_d); 
            deskripsi.setText(des_d);
        }
    }
}

JSONParser.java

public class JSONParser {
    static InputStream is = null; 
    static JSONObject jObj = null;
    static String json = "";

    //  constructor 
    public JSONParser() {
    }

    public JSONObject getJSONFromUrl(String url) {
        // Making HTTP request 
        try {

            // defaultHttpClient
            DefaultHttpClient httpClient = new DefaultHttpClient(); 
            HttpPost httpPost = new HttpPost(url);
            HttpResponse httpResponse = httpClient.execute(httpPost); 
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();
        }

        catch (UnsupportedEncodingException e) { 
            e.printStackTrace();
        }

        catch (ClientProtocolException e) { 
            e.printStackTrace();
        }

        catch (IOException e) {
            e.printStackTrace();
        }

        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(is, "iso-8859-1"), 8);

            StringBuilder sb = new StringBuilder(); 
            String line = null;

            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }

            is.close();
            json = sb.toString();
        }

        catch (Exception e) {
            Log.e("Buffer Error", "Error converting result " +e.toString());
        }

        // try parse the string to a JSON object 
        try {
            jObj = new JSONObject(json);
        }

        catch (JSONException e) {
            Log.e("JSON Parser", "Error parsing data " +e.toString());
        }

        // return JSON String 
        return jObj;
    }

    public JSONObject makeHttpRequest(String url, String method, List<NameValuePair> params) {

        // Making HTTP request 
        try {
            // check for request method 
            if (method == "POST") {

                // request method is POST
                // defaultHttpClient 
                DefaultHttpClient httpClient = new DefaultHttpClient();
                HttpPost httpPost = new HttpPost(url); 
                httpPost.setEntity(new UrlEncodedFormEntity(params)); 
                HttpResponse httpResponse = httpClient.execute(httpPost);
                HttpEntity httpEntity = httpResponse.getEntity(); 
                is = httpEntity.getContent();
            }

            else if (method == "GET") {
                // request method is GET 
                DefaultHttpClient httpClient = new DefaultHttpClient();
                String paramString = URLEncodedUtils.format(params, "utf-8"); 
                url += "?" + paramString;
                HttpGet httpGet = new HttpGet(url); 
                HttpResponse httpResponse = httpClient.execute(httpGet);
                HttpEntity httpEntity = httpResponse.getEntity(); 
                is = httpEntity.getContent();
            }
        }

        catch (UnsupportedEncodingException e) { 
            e.printStackTrace();
        }

        catch (ClientProtocolException e) { 
            e.printStackTrace();
        }

        catch (IOException e) { 
            e.printStackTrace();
        }

        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(is, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder(); 
            String line = null;

            while ((line = reader.readLine()) != null) { 
                sb.append(line + "\n");
            }

            is.close();
            json = sb.toString();
        }

        catch (Exception e) {
            Log.e("Buffer Error", "Error converting result " +e.toString());
        }

        // try parse the string to a JSON object 
        try {
            jObj = new JSONObject(json);
        }

        catch (JSONException e) {
            Log.e("JSON Parser", "Error parsing data " +e.toString());
        }

        // return JSON String 
        return jObj;
    }
}

Answer 1

这是因为您没有从 doInBackground() 返回任何值(始终返回 null)，并且您没有在 onPostExecute(String result)< 中使用“字符串” 形式参数。垃圾进垃圾出