java - 解析 JSON 数据时出错 - 异步任务

Question

我收到错误 Error parsing Data，这是我在解析 JSON 数据时在主要异常中捕获的。

但是 - 我的错误 No Data Found 没有被 JSONException 捕获，这让我认为数据库被成功读取，

我的服务器上有一个 php 文件:

<?php

mysql_connect("database_ip","database_username","database_password");
mysql_select_db("database_name");

$sql=mysql_query("select * from table");
while($row=mysql_fetch_assoc($sql))
$output[]=$row;
print(json_encode($output));// this will print the output in json

mysql_close();
?>

在线导航到 php 文件会按预期显示 JSON 数据:

[{"KEY_ROWID":"1","KEY_NAME":"Andrew","KEY_SCORE":"100","KEY_DATE":"0000-00-00 00:00:00"}, {"KEY_ROWID":"2","KEY_NAME":"Peter","KEY_SCORE":"5000","KEY_DATE":"2013-11-29 10:58:21"}]

在 Android 中，我使用 Async 任务来读取数据:

class Task extends AsyncTask<String, String, Void> {
        InputStream is = null;
        String result = "";

        @Override
        protected Void doInBackground(String... params) {
            // TODO Auto-generated method stub
            String url_select = "http://mywebsite.com/myphpfile.php";

            HttpClient httpClient = new DefaultHttpClient();
            HttpPost httpPost = new HttpPost(url_select);

            ArrayList<NameValuePair> param = new ArrayList<NameValuePair>();

            try {
                httpPost.setEntity(new UrlEncodedFormEntity(param));

                HttpResponse httpResponse = httpClient.execute(httpPost);
                HttpEntity httpEntity = httpResponse.getEntity();

                // read content
                is = httpEntity.getContent();

            } catch (Exception e) {

                Log.e("log_tag", "Error in http connection " + e.toString());
            }
            try {
                BufferedReader br = new BufferedReader(
                        new InputStreamReader(is));
                StringBuilder sb = new StringBuilder();
                String line = "";
                while ((line = br.readLine()) != null) {
                    sb.append(line + "\n");
                }
                is.close();
                result = sb.toString();

            } catch (Exception e) {
                // TODO: handle exception
                Log.e("log_tag", "Error converting result " + e.toString());
            }

            return null;
        }

        protected void onPostExecute(Void v) {
            try {

                JSONArray Jarray = new JSONArray(result);
                for (int i = 0; i < Jarray.length(); i++) {
                    JSONObject Jasonobject = Jarray.getJSONObject(i);
                    text = (TextView) findViewById(R.id.textView1);
                    // get an output on the screen
                    String name = Jasonobject.getString("KEY_NAME");
                    text.append(name + "\n");

                }

            }

            catch (JSONException e1) {
                Toast.makeText(getBaseContext(), "NO Data Found",
                        Toast.LENGTH_LONG).show();
            }

            catch (Exception e) {
                // TODO: handle exception
                Log.e("log_tag", "Error parsing data " + e.toString());
            }

        }

    }

在我的 Activity onCreate 中，我实例化了异步类:

new Task().execute();

对于为什么解析数据出错有什么建议吗？

谢谢

注意:使用 println() 输出变量 'result' 会按预期将 Json 输出到 logcat

Answer 1

形成你的代码:

...
catch (Exception e) {
            // TODO: handle exception
            Log.e("log_tag", "Error parsing data " + e.toString());
        }

问题是它可能不是 Json 异常，而是 any 异常。实际上，不建议捕获 Exception 类型。我们应该只捕获 Exception 类的特定子类型。在我们的例子中，findViewById 抛出:NullPointerException。因此，首先将其更改为 NullPointerException(除了 JSONException 之外)并再次运行程序。

我会将 Error parsing data 更改为通用的内容。

假设我们在 findViewById 上没有异常并且我们的 text 不是 null。

尝试使用Handler 更新主线程(又名 GUI):

private Handler mHandler = null;

 ...

 mHandler = new Handler();

 ... 

    mHandler.postDelayed(new Runnable() {
            @Override
            public void run() {
                try {
                    text = (TextView) findViewById(R.id.textView1);
                    JSONArray Jarray = new JSONArray(result);
                    for (int i = 0; i < Jarray.length(); i++) {
                        JSONObject Jasonobject = Jarray.getJSONObject(i);

                        // get an output on the screen
                        String name = Jasonobject.getString("KEY_NAME");
                        text.append(name + "\n");
                    }
                }

                catch (JSONException e1) {
                    Toast.makeText(getBaseContext(), "NO Data Found",
                            Toast.LENGTH_LONG).show();
                }

                catch (NullPointerException e) {
                    // TODO: handle exception
                    Log.e("log_tag", "Error  " + e.toString());
                }
            }
        }, 100); // dummy delay

作为旁注:

行 text = (TextView) findViewById(R.id.textView1); 放在循环之外 for