Android null object reference on JsonArray.toString() using

Question

im 在网站和 android 应用程序上工作。 我使用 koush/ion 库 我现在正在努力解决这个问题，其中 JSON 为空，我已经确认了这一点

System.out.print(result(;

我目前正在测试这段代码，以了解 JSON Object 和 jsonarray 在 Android 中的工作原理。 我是 JSON 的初学者。 我还尝试将 JSON 数组插入我的表视图中

这是安卓活动

public class TestActivity extends AppCompatActivity {
TableLayout usertabletest;
static JSONArray arr = null;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.test);
    usertabletest = (TableLayout) findViewById(R.id.usertabletest);
    View tablehead = LayoutInflater.from(this).inflate(R.layout.testlol, null, false);
    TextView idhead = (TextView) tablehead.findViewById(R.id.idtest);
    TextView useridhead = (TextView) tablehead.findViewById(R.id.useridtest);
    TextView passwordhead = (TextView) tablehead.findViewById(R.id.passwordtest);
    TextView rolehead = (TextView) tablehead.findViewById(R.id.roletest);
    idhead.setText("id");
    useridhead.setText("userid");
    passwordhead.setText("password");
    rolehead.setText("role");
    usertabletest.addView(tablehead);
    Ion.with(this)
            .load("http://267.site11.com/doubletime-app/sql.php")
            .asJsonArray()
            .setCallback(new FutureCallback<JsonArray>() {
                @Override
                public void onCompleted(Exception e, JsonArray result) {
                    try {
                        JSONArray arr = new JSONObject(result.toString()).getJSONArray("posts");
                        // get the 'posts' section from the JSON string
                        for (int i = 0; i < arr.length(); i++) {
                            JSONObject post = arr.getJSONObject(i).getJSONObject("post");
                            String id = post.getString("id");
                            String userid = post.getString("userid");
                            String password = post.getString("password");
                            String role = post.getString("role");
                            buildtable(id, userid, password, role);
                        }
                    } catch (JSONException E) {
                        E.printStackTrace();
                    }
                }
            });
}

这是我的 SQL.php

<?php
    include 'JSON.php';
    $query = "SELECT * FROM user_accounts";
    encodequery($query);
?>

这是 JSON

.php

<?php
function encodequery($query) {
$dbhost = "localhost";
$dbuser = "id1341573_267admin";
$db = "id1341573_rotc";
$dbpass = "iloveyou267";
$conn = new mysqli($dbhost, $dbuser, $dbpass,$db) or die("Connect failed: %sn". $conn -> error);
$result = mysqli_query($conn, $query) or die(mysqli_error($conn));
$posts = array();
if(mysqli_fetch_array($result)) {
  while($post = mysqli_fetch_assoc($result)) {
     $posts[] = array('post'=>$post);
     }
   }
encodearray($posts);
}
function encodearray($posts) {
header('Content-type: application/json');
echo json_encode(array('posts'=>$posts));
}
?>

Answer 1

试试这个

[ 和 { –(方括号和大括号(之间的区别

如果你的JSON节点以[开头，那么我们应该使用getJSONArray((方法。就像节点以 { 开头一样，那么我们应该使用 getJSONObject(( 方法。

Ion.with(context)
            .load(url)
            .asJsonObject()
            .setCallback(new FutureCallback<JsonObject>() {
                @Override
                public void onCompleted(Exception e, JsonObject result) {
                    // TODO
                   try 
                   {
                      JSONArray arr  = result.getJSONArray("posts");
                      for (int i = 0; i < arr.length(); i++)
                      {
                         JSONObject post = arr.getJSONObject(i).getJSONObject("post");
                         String id = post.getString("id");
                         String userid = post.getString("userid");
                         String password = post.getString("password");
                         String role = post.getString("role");
                         String syncsts = post.getString("syncsts");
                         Log.i("ID "," "+id);
                         Log.i("User id "," "+userid);
                         Log.i("Password "," "+password);
                         Log.i("Role "," "+role);
                         Log.i("Syncsts "," "+syncsts);
                         buildtable(id, userid, password, role);
                     }
                } catch (JSONException E) {
                    E.printStackTrace();
                }
                }
            });