Question

每当我试图打开这个应用程序时，我都会收到此错误。我正在解析来自我本地主机的数据。我没有得到什么是错误..我是android的新手，我也不擅长阅读logcat 任何人都可以解决这个问题....在此之前感谢...

MainActivity：

package com.newjson;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;


public class MainActivity extends Activity {

    private static String url = "http://10.0.2.2:80/sample/";

    private static final String TAG_RESPONSE = "response";
    private static final String TAG_NAME = "RetailerName";
    private static final String TAG_EMAIL = "Email";
    private static final String TAG_PHONE = "Phone";
    private static final String TAG_ADDRESS = "Address";

    JSONArray response = null;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        JSONParser parser = new JSONParser();

        JSONObject jobj = parser.getJSONFromUrl(url);

        try{
            response = jobj.getJSONArray(TAG_RESPONSE);

            JSONObject c = response.getJSONObject(0);

            String name = c.getString(TAG_NAME);
            String email = c.getString(TAG_EMAIL);
            String phone = c.getString(TAG_PHONE);
            String address = c.getString(TAG_ADDRESS);

            TextView name1 = (TextView)findViewById(R.id.name);
            TextView email1 = (TextView)findViewById(R.id.email);
            TextView phone1 = (TextView)findViewById(R.id.phone);
            TextView address1 = (TextView)findViewById(R.id.address);

            name1.setText(name);
            email1.setText(email);
            phone1.setText(phone);
            address1.setText(address);
        }catch(JSONException e){
            e.printStackTrace();
        }
    }
}

JSONParser ：

package com.newjson;

    import java.io.BufferedReader;
    import java.io.IOException;
    import java.io.InputStream; 
    import java.io.InputStreamReader;
    import java.io.UnsupportedEncodingException;

    import org.apache.http.HttpEntity;
    import org.apache.http.HttpResponse;
    import org.apache.http.client.ClientProtocolException;
    import org.apache.http.client.methods.HttpPost;
    import org.apache.http.impl.client.DefaultHttpClient;
    import org.json.JSONObject;

    import android.util.Log;

    public class JSONParser {

    static InputStream is = null;
    static JSONObject jobj = null;
    static String json = "";

    public JSONParser(){

    }
    public JSONObject getJSONFromUrl(String url){
        try{
            DefaultHttpClient client = new DefaultHttpClient();
            HttpPost post = new HttpPost();
            HttpResponse respose = client.execute(post);
            HttpEntity entity = respose.getEntity();
            is = entity.getContent();

        }catch(UnsupportedEncodingException e){
            e.printStackTrace();
        }catch(ClientProtocolException e){
            e.printStackTrace();
        }catch(IOException e){
            e.printStackTrace();
        }
        try{
            BufferedReader br = new BufferedReader(new InputStreamReader(is, "iso-8859-1"),8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while((line = br.readLine())!= null){
                sb.append(line + "\n");

            }
            is.close();
            json = sb.toString();
        }catch(Exception e){
            Log.e("buffer error", "error converting result"+e.toString());
        }
        return jobj;
    }

}

logcat的：

11-26 12:15:50.296: D/AndroidRuntime(639): Shutting down VM
11-26 12:15:50.296: W/dalvikvm(639): threadid=1: thread exiting with uncaught exception        (group=0x40015560)
11-26 12:15:50.330: E/AndroidRuntime(639): FATAL EXCEPTION: main
11-26 12:15:50.330: E/AndroidRuntime(639): java.lang.RuntimeException: Unable to start activity     ComponentInfo{com.newjson/com.newjson.MainActivity}: java.lang.NullPointerException
11-26 12:15:50.330: E/AndroidRuntime(639):  at   android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
11-26 12:15:50.330: E/AndroidRuntime(639):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
11-26 12:15:50.330: E/AndroidRuntime(639):  at android.app.ActivityThread.access$1500(ActivityThread.java:117)
11-26 12:15:50.330: E/AndroidRuntime(639):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
11-26 12:15:50.330: E/AndroidRuntime(639):  at android.os.Handler.dispatchMessage(Handler.java:99)
11-26 12:15:50.330: E/AndroidRuntime(639):  at android.os.Looper.loop(Looper.java:123)
11-26 12:15:50.330: E/AndroidRuntime(639):  at android.app.ActivityThread.main(ActivityThread.java:3683)
11-26 12:15:50.330: E/AndroidRuntime(639):  at java.lang.reflect.Method.invokeNative(Native Method)
11-26 12:15:50.330: E/AndroidRuntime(639):  at java.lang.reflect.Method.invoke(Method.java:507)
11-26 12:15:50.330: E/AndroidRuntime(639):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
11-26 12:15:50.330: E/AndroidRuntime(639):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
11-26 12:15:50.330: E/AndroidRuntime(639):  at dalvik.system.NativeStart.main(Native Method)
11-26 12:15:50.330: E/AndroidRuntime(639): Caused by: java.lang.NullPointerException
11-26 12:15:50.330: E/AndroidRuntime(639):  at  org.apache.http.impl.client.AbstractHttpClient.determineTarget(AbstractHttpClient.java:496)
11-26 12:15:50.330: E/AndroidRuntime(639):  at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487)
11-26 12:15:50.330: E/AndroidRuntime(639):  at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465)
11-26 12:15:50.330: E/AndroidRuntime(639):  at com.newjson.JSONParser.getJSONFromUrl(JSONParser.java:31)
11-26 12:15:50.330: E/AndroidRuntime(639):  at com.newjson.MainActivity.onCreate(MainActivity.java:32)
11-26 12:15:50.330: E/AndroidRuntime(639):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
11-26 12:15:50.330: E/AndroidRuntime(639):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
11-26 12:15:50.330: E/AndroidRuntime(639):  ... 11 more

这是永远存在的： enter image description here

Answer 1

你的post变量在这一行中抛出空指针异常

 HttpPost post = new HttpPost();

只需将网址添加为参数

即可

 HttpPost post = new HttpPost(url);

Answer 2

请勿使用HttpPost，您要做的事情是HttpGet。使用;

更改getJSONFromUrl方法

public JSONObject getJSONFromUrl(String url){
    try{
        HttpParams httpParameters = new BasicHttpParams();
        HttpClient client = new DefaultHttpClient(httpParameters);
        HttpGet httpget = new HttpGet(url);
        HttpResponse respose = client.execute(httpget);
        HttpEntity entity = respose.getEntity();
        is = entity.getContent();

    }catch(UnsupportedEncodingException e){
        e.printStackTrace();
    }catch(ClientProtocolException e){
        e.printStackTrace();
    }catch(IOException e){
        e.printStackTrace();
    }
    try{
        BufferedReader br = new BufferedReader(new InputStreamReader(is, "iso-8859-1"),8);
        StringBuilder sb = new StringBuilder();
        String line = null;
        while((line = br.readLine())!= null){
            sb.append(line + "\n");

        }
        is.close();
        json = sb.toString();
    }catch(Exception e){
        Log.e("buffer error", "error converting result"+e.toString());
    }
    return jobj;
}

最后，您必须在AsyncTask上进行网络操作。使用;

更改您的MainActivity代码

public class MainActivity extends Activity {

    private static String url = "http://10.0.2.2:80/sample/";

    private static final String TAG_RESPONSE = "response";
    private static final String TAG_NAME = "RetailerName";
    private static final String TAG_EMAIL = "Email";
    private static final String TAG_PHONE = "Phone";
    private static final String TAG_ADDRESS = "Address";
    private ProgressDialog progressDialog;
    private YourTask task;

    JSONArray response = null;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        task = new YourTask();
        progressDialog = ProgressDialog.show(MainActivity.this, "", "Downloading...",true ,false);
        task.execute();

    }

    public class YourTask extends AsyncTask<Void, Void, JSONObject>{

        @Override
        protected Void doInBackground(Void... arg0) {   
            JSONParser parser = new JSONParser();
            JSONObject jobj = parser.getJSONFromUrl(url);
            return jobj;
        }

        @Override
        protected void onPostExecute(JSONObject jobj) {
            try{
                response = jobj.getJSONArray(TAG_RESPONSE);

                JSONObject c = response.getJSONObject(0);

                String name = c.getString(TAG_NAME);
                String email = c.getString(TAG_EMAIL);
                String phone = c.getString(TAG_PHONE);
                String address = c.getString(TAG_ADDRESS);

                TextView name1 = (TextView)findViewById(R.id.name);
                TextView email1 = (TextView)findViewById(R.id.email);
                TextView phone1 = (TextView)findViewById(R.id.phone);
                TextView address1 = (TextView)findViewById(R.id.address);

                name1.setText(name);
                email1.setText(email);
                phone1.setText(phone);
                address1.setText(address);
            }catch(JSONException e){
                e.printStackTrace();
            }
            progressDialog.dismiss();
        }

        @Override
        protected void onCancelled() {
            task = null;
            progressDialog.dismiss();
        }
    }
}

Json解析..强制关闭错误

2 个答案: