线 - > JSONArray jArray = new JSONArray(result);给出nullpointer异常 [英] Line -> JSONArray jArray=new JSONArray(result); giving nullpointer exception
问题描述
package com.example.fyptrialapp;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.HashMap;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONArray;
import org.json.JSONObject;
import android.app.Activity;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.StrictMode;
import android.text.Editable;
import android.text.TextWatcher;
import android.util.Log;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.AutoCompleteTextView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Toast;
public class SearchByName extends Activity{
HttpPost httppost;
StringBuffer buffer;
HttpResponse response;
HttpClient httpclient;
InputStream inputStream=null;
Intent i;
//public static final String recipes[]=new String[]{"Almond-Sheera","Bhel","Bread-Pizzas","Carrot-Pickle","Carrot-Relish"};
String recipes[];
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.search_recipe);
StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);
Button b2=(Button)findViewById(R.id.bSearchByName);
try{
httpclient = new DefaultHttpClient();
httppost = new HttpPost("http://10.0.2.2/fypTrial2/searchByName.php");
response = httpclient.execute(httppost); // Execute HTTP Post Request
inputStream = response.getEntity().getContent();
String result=null;
BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, "iso-8859-1"), 8);
StringBuilder sb = new StringBuilder();
String line=null;
while((line=reader.readLine())!= null){
sb.append(line+"\n");
}
inputStream.close();
result=sb.toString();
JSONArray jArray=new JSONArray(result);// this statment gives error
for(int i=0;i<jArray.length();i++){
JSONObject json=jArray.getJSONObject(i);
recipes[i]=json.getString("name");
}
}
catch(Exception e){
Log.e("log_tag3", "Error convering result"+e.toString());
}
ArrayAdapter<String> ac=new ArrayAdapter<String>(this,android.R.layout.simple_dropdown_item_1line,recipes);
AutoCompleteTextView tv=(AutoCompleteTextView) findViewById(R.id.autoCompleteTextView2);
tv.setAdapter(ac);
b2.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Intent i=new Intent("com.example.practice.Search_Result");
startActivity(i);
}
});
}
}
错误
java.nullpointerexception。转换结果变量时出错。
致命主要错误
java.nullpointerexception. Error converting result variable.And the fatal main error
如果我想使用ASnk任务,我该怎么写?
If i want to use ASnk task how should i write it.
推荐答案
JSON语法不会作为数组启动。可能是以{随后[,但从不直接[]开始。这就是为什么试图把你的结果转换成JSONArray是不行的。您应该尝试首先获取对象,然后获取数组元素。
JSON syntax never starts as an array. It could be that it starts with { followed by [, but never straight to [. This is why trying to convert your results to JSONArray will not work. You should therefor try to get the object first, then the array elements.
JSONObject jo = new JSONObject(result);
JSONArray jArray = jo.getJSONArray("keyIdentifyer");
如果没有数组键识别器,可以尝试迭代或获取第一个元素。不存在任何键时,请参阅此帖子answear 。
If you dont have the array key identifyer, you could try to iterate or get the first element. See this post answear on iterations when no keys are present.
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