java - 在 Android 上执行 AsyncTask/发布 JSON

Question

我正在开发一个 Android 应用程序，但在注册用户时遇到了一些麻烦。我想将一个 JSON 对象发布到我的服务器并收到一个返回。我可以使用正确的信息成功创建一个 JSON 对象，但是当我发布它时，我得到一个 NetworkOnMainThreadException 或我的 HttpClient 类在它应该返回一个 JSONObject 时返回 null，我非常有信心我的 Web 服务器可以正常工作。我知道您无法在主线程上连接到网络并创建了一个使用 AsnycTask 的 HttpClient 类(尽管可能不正确)。我已经为此工作了很长一段时间，并希望在正确的方向上得到任何指导。

//Main activity
@Override
public void onClick(View arg0) {
    if(!(isEmpty(name) || isEmpty(username) || isEmpty(password) || isEmpty(email))) {
        user = new JSONObject();
        try {
            user.put("username", username.getText().toString());
            user.put("name", name.getText().toString());
            user.put("email", email.getText().toString());
            user.put("password", password.getText().toString());
        } catch (JSONException e) {
            e.printStackTrace();
        }

        jRegister = new JSONObject();

        try {
            jRegister.put("apiToken", Utilities.apiToken);
            jRegister.put("user", user);

            Log.i("MainActivity", jRegister.toString(2));

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

       //
        HttpClient client = new HttpClient(url, jRegister);
        result = client.getJSONFromUrl();


        try {
            if(result  != null)
                tv.setText(result.toString(2));
            else
                 tv.setText("null");
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }else {
        tv.setText("");
    }
}

HttpClient 类

public class HttpClient extends AsyncTask<Void, Void, JSONObject>{
    private final String TAG = "HttpClient";
    private String URL;
    private JSONObject jsonObjSend;
    private JSONObject result = null;

    public HttpClient(String URL, JSONObject jsonObjSend) {
        this.URL = URL;
        this.jsonObjSend = jsonObjSend;
    }

    public JSONObject getJSONFromUrl() {
        this.execute();
        return result;
    }

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

            try {
                    DefaultHttpClient httpclient = new DefaultHttpClient();
                    HttpPost httpPostRequest = new HttpPost(URL);

                    StringEntity se;
                    se = new StringEntity(jsonObjSend.toString());

                    // Set HTTP parameters
                    httpPostRequest.setEntity(se);
                    httpPostRequest.setHeader("Accept", "application/json");
                    httpPostRequest.setHeader("Content-type", "application/json");

                    long t = System.currentTimeMillis();
                    HttpResponse response = (HttpResponse) httpclient.execute(httpPostRequest);
                    Log.i(TAG, "HTTPResponse received in [" + (System.currentTimeMillis()-t) + "ms]");

                    HttpEntity entity = response.getEntity();

                    if (entity != null) {
                            // Read the content stream
                            InputStream instream = entity.getContent();

                            // convert content stream to a String
                            String resultString= convertStreamToString(instream);
                            instream.close();
                            resultString = resultString.substring(1,resultString.length()-1); // remove wrapping "[" and "]"

                            JSONObject jsonObjRecv = new JSONObject(resultString);

                            // Raw DEBUG output of our received JSON object:
                            Log.i(TAG,"<JSONObject>\n"+jsonObjRecv.toString()+"\n</JSONObject>");

                            return jsonObjRecv;
                    } 

            }
            catch (Exception e) {
                    e.printStackTrace();
            }
            return null;
    }

    protected void onPostExecute(JSONObject jObject) {
        result = jObject;
    }
    private static String convertStreamToString(InputStream is) {

            BufferedReader reader = new BufferedReader(new InputStreamReader(is));
            StringBuilder sb = new StringBuilder();

            String line = null;
            try {
                    while ((line = reader.readLine()) != null) {
                            sb.append(line + "\n");
                    }
            } catch (IOException e) {
                    e.printStackTrace();
            } finally {
                    try {
                            is.close();
                    } catch (IOException e) {
                            e.printStackTrace();
                    }
            }
            return sb.toString();
    }

Answer 1

I understand that you cannot connect to the network on the main thread and have created an HttpClient class that uses AsnycTask (although probably not correctly).

你是对的，你没有以正确的方式实现它。

在您的 onClick 事件中(仍在主线程上)您执行了导致错误的网络 Activity :

HttpClient client = new HttpClient(url, jRegister);
result = client.getJSONFromUrl();

相反，您应该在 AsnycTask 中运行网络操作

public class GetJsonTask extends AsyncTask<Void, Void, JSONObject >{
    private String URL;
    private JSONObject jsonObjSend;

    public GetJsonTask(String URL, JSONObject jsonObjSend) {
        this.URL = URL;
        this.jsonObjSend = jsonObjSend;
    }

    @Override
    protected JSONObject doInBackground(Void... params) {
    JSONObject jsonObjRecv;
           try {
                    DefaultHttpClient httpclient = new DefaultHttpClient();
                    HttpPost httpPostRequest = new HttpPost(URL);

                    StringEntity se;
                    se = new StringEntity(jsonObjSend.toString());

                    // Set HTTP parameters
                    httpPostRequest.setEntity(se);
                    httpPostRequest.setHeader("Accept", "application/json");
                    httpPostRequest.setHeader("Content-type", "application/json");

                    long t = System.currentTimeMillis();
                    HttpResponse response = (HttpResponse) httpclient.execute(httpPostRequest);
                    Log.i(TAG, "HTTPResponse received in [" + (System.currentTimeMillis()-t) + "ms]");

                    HttpEntity entity = response.getEntity();

                    if (entity != null) {
                            // Read the content stream
                            InputStream instream = entity.getContent();

                            // convert content stream to a String
                            String resultString= convertStreamToString(instream);
                            instream.close();
                            resultString = resultString.substring(1,resultString.length()-1); // remove wrapping "[" and "]"

                            jsonObjRecv = new JSONObject(resultString);

                            // Raw DEBUG output of our received JSON object:
                            Log.i(TAG,"<JSONObject>\n"+jsonObjRecv.toString()+"\n</JSONObject>");


                    } 

            }
            catch (Exception e) {
                    e.printStackTrace();
            }
            return jsonObjRecv;         
    }

    protected void onPostExecute(JSONObject result) {
        try {
            if(result  != null)
                tv.setText(result.toString(2));
            else
                 tv.setText("null");
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }else {
        tv.setText("");
    }
    }

}

然后你像这样在 onclik 方法中调用你的异步:

public void onClick(View arg0) {
//.......
GetJsonTask client = new GetJsonTask(url, jRegister);
client.execute();
}