我是Android新手,我一直在尝试使用PHP和MYSQL进行JSON解析,当我运行app时出现此错误 .
Error:
FATAL EXCEPTION:main进程:com.example.admin.androidjsonparsing,PID:13399 java.lang.NullPointerException:尝试在org.json的空对象引用上调用虚方法'int java.lang.String.length()' .JSONTokener.nextCleanInternal(JSONTokener.java:116)位于org.json.JSONArray的org.json.JSONTokener.nextValue(JSONTokener.java:94) . (JSONArray.java:92)org.json.JSONArray . (JSONArray . java:108)com.example.admin上的com.example.admin.androidjsonparsing.MainActivity.loadIntoListView(MainActivity.java:79)com.example.admin的com.example.admin.androidjsonparsing.MainActivity.access $ 000(MainActivity.java:22) . 在android.os.AsyncTask.finish(AsyncTask.java:695)的com.example.admin.androidjsonparsing.MainActivity $ 1GetJSON.onPostExecute(MainActivity.java:38)上的androidjsonparsing.MainActivity $ 1GetJSON.onPostExecute(MainActivity.java:51)在Android.os.Handler.dispatchMessag的android.os.AsyncTask.access $ 600(AsyncTask.java:180)android.os.AsyncTask $ InternalHandler.handleMessage(AsyncTask.java:712) e(Handler.java:106)位于android.app.Looper.loop(Looper.java:193)的android.app.ActivityThread.main(ActivityThread.java:6669)at java.lang.reflect.Method.invoke(Native方法)在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)的com.android.internal.os.RuntimeInit $ MethodAndArgsCaller.run(RuntimeInit.java:493)
这里 code:
MainActivity.java
package com.example.admin.androidjsonparsing;
import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
public class MainActivity extends AppCompatActivity {
ListView listView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listView = (ListView) findViewById(R.id.listView);
getJSON("http://192.168.1.4/AndroidJSONParsing/getdata.php");
}
private void getJSON(final String urlWebService) {
class GetJSON extends AsyncTask<Void, Void, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
Toast.makeText(getApplicationContext(), s, Toast.LENGTH_SHORT).show();
try {
loadIntoListView(s);
} catch (JSONException e) {
e.printStackTrace();
}
}
@Override
protected String doInBackground(Void... voids) {
try {
URL url = new URL(urlWebService);
HttpURLConnection con = (HttpURLConnection) url.openConnection();
StringBuilder sb = new StringBuilder();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(con.getInputStream()));
String json;
while ((json = bufferedReader.readLine()) != null) {
sb.append(json + "\n");
}
return sb.toString().trim();
} catch (Exception e) {
return null;
}
}
}
GetJSON getJSON = new GetJSON();
getJSON.execute();
}
private void loadIntoListView(String json) throws JSONException {
JSONArray jsonArray = new JSONArray(json);
String[] heroes = new String[jsonArray.length()];
for (int i = 0; i < jsonArray.length(); i++) {
JSONObject obj = jsonArray.getJSONObject(i);
heroes[i] = obj.getString("name");
}
ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, heroes);
listView.setAdapter(arrayAdapter);
}
}
activity_main.xml中
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.admin.androidjsonparsing.MainActivity">
<!-- this is our listview where we will display the fetched data -->
<ListView
android:id="@+id/listView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentTop="true" />
</RelativeLayout>
3 回答
检查空字符串 .
试试这个代码......
问题是因为您的
String json
不是有效的json,可能是因为它是null
或bad formated json
,然后尝试如下:第1步 .
第2步 .