[更新]如何从json对象访问值？

Question

I am completely new to android & JSON. Please help me out to find a solution for this problem-- Below is my php code.

    <?php 
require "conn.php";
header('Content-Type: application/json');
if(isset($_POST['mailid']))
{
    $mailid = $_POST['mailid'];
    $today="2017-05-05";//date('Y-m-d');
    $mysql_qry = "select employee_id from employee where employee_email='$mailid';";
    $result = mysqli_query($conn ,$mysql_qry);
    $row = mysqli_fetch_array($result);

    $emp_id=$row['employee_id'];
    if($emp_id)
    {
        $sql = "SELECT count(*) from task where employee_id='$emp_id' and task_date='$today';";
        $result1 = mysqli_query($conn ,$sql);
        $row2=mysqli_fetch_array($result1, MYSQL_ASSOC);

        if($result1) 
        {
            $taskcount['count']= $row2['count(*)'];
            $taskquery = "select task_name from task where employee_id='$emp_id' and task_date='$today';";
            $restask_name=mysqli_query($conn ,$taskquery);

            for($i=0;$row1=mysqli_fetch_array($restask_name);$i++)
            {
                $task_name[]= $row1[0];
            }
            $taskname['tasks']=$task_name;
            $array=array_merge($taskcount,$taskname);
            echo json_encode($array);
        }
        else 
        {
        echo json_encode($taskcount);
        }
    }
    else
    {
        echo "employee ID doesnt match!!";
    }
}
else
{
    echo "post variables are not set";
}
?>

I am getting a response from server like below--

{
 "count": "4",
 "tasks": [
        "collect paper",
        "krishna",
        "mys",
        "bng"   ] 
}

My code to parse json object is as follows--

if (!result.equals("employee ID doesnt match!!") || !result.equals("post variables are not set")) {
                    JSONObject json = new JSONObject(result);

                    MAX_ROWS = Integer.parseInt(json.getString("count"));
                    System.out.println("rows:"+MAX_ROWS);
                    JSONArray tasks = json.getJSONArray("tasks");
                    for (int task_id = 0; task_id < MAX_ROWS; task_id++) {
                        taskname[task_id] = tasks.getString(task_id);//**LINE 153**
                        System.out.println(taskname[task_id]);
                    }

                }

Now I m getting an Null Pointer Exception,Here is my Stacktrace--

05-05 17:41:33.255 22823-23024/com.example.anusha.fieldworkemployeetracker W/System.err:java.lang.NullPointerException
05-05 17:41:33.396 22823-23024/com.example.anusha.fieldworkemployeetracker W/System.err:     at com.example.anusha.fieldworkemployeetracker.ViewtaskActivity$BackgroundWorker.doInBackground(ViewtaskActivity.java:153)
05-05 17:41:33.396 22823-23024/com.example.anusha.fieldworkemployeetracker W/System.err:     at com.example.anusha.fieldworkemployeetracker.ViewtaskActivity$BackgroundWorker.doInBackground(ViewtaskActivity.java:107)
05-05 17:41:33.396 22823-23024/com.example.anusha.fieldworkemployeetracker W/System.err:     at android.os.AsyncTask$2.call(AsyncTask.java:288)
05-05 17:41:33.396 22823-23024/com.example.anusha.fieldworkemployeetracker W/System.err:     at java.util.concurrent.FutureTask.run(FutureTask.java:237)
05-05 17:41:33.396 22823-23024/com.example.anusha.fieldworkemployeetracker W/System.err:     at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
05-05 17:41:33.396 22823-23024/com.example.anusha.fieldworkemployeetracker W/System.err:     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
05-05 17:41:33.396 22823-23024/com.example.anusha.fieldworkemployeetracker W/System.err:     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
05-05 17:41:33.396 22823-23024/com.example.anusha.fieldworkemployeetracker W/System.err:     at java.lang.Thread.run(Thread.java:841)

How can I do that? Thanks in Advance.

Answer 1

Try following code:

if (!result.equals("employee ID doesnt match!!") || !result.equals("post variables are not set")) {
                    JSONObject json = new JSONObject(result);
                    //JSONObject count = json.getJSONObject("task" + task_id);
                    JSONArray count = json.getJSONArray("count");
                    MAX_ROWS = Integer.parseInt(count.getString(0));
                    System.out.println("rows:" + MAX_ROWS);
                    for (int task_id = 0; task_id < MAX_ROWS; task_id++) {
                        JSONArray task = json.getJSONArray("task" + String.valueOf(task_id));
                        taskname[task_id] = task.getString(0);
                        System.out.println(taskname[task_id]);
                    }

                }

Answer 2

make Json like ;

       { "count": 
            "4"
          ,
          "tasks0": 
            "collect paper"
          ,
          "tasks1": 
            "krishna"
          ,
          "tasks2": 
            "mys"
          ,
          "tasks3": 
            "bng"
}

Then To parse above JSON use following code;

 JSONObject json = new JSONObject(jsonResponseString);
  String countValue = json.getString("count");

Answer 3

There are several mistakes in your code:

1. Here you are trying to access JSONArray, using the code of JSONObject . Eg: count is JSONArray . So you should parse it as JSONArray . like this:

    MAX_ROWS = json.getJSONArray("count").getInt(0); 

2. key name is tasks in JSONObject, you should use proper name for that.

    JSONArray tasks = json.getJSONArray("tasks" + task_id); 

3. task_name is also a JSONArray , so you should handle that accordingly.

So working code should be like this:

MAX_ROWS = json.getJSONArray("count").getInt(0);
for (int task_id = 0; task_id < MAX_ROWS; task_id++) {
     JSONArray tasks = json.getJSONArray("tasks" + task_id);
     taskname[task_id] = task.getString("task_name");
     System.out.println(taskname[task_id]);
}

Answer 4

This might solve your problem

JSONObject json = new JSONObject(result);
MAX_ROWS = json.getJSONArray("count").getInt(0);
System.out.println("rows:" + MAX_ROWS);
for (int task_id = 0; task_id < MAX_ROWS; task_id++) {
    JSONArray task = json.getJSONArray("tasks" + task_id);
    taskname[task_id] = task.getString(0);
    System.out.println(taskname[task_id]);
}

However I think there is a more structural problem with your JSON String, which makes it difficult to parse into an object. Namely you're storing everything as a JSONArray (instead of their actual types, eg int or String).

Personally I would consider structuring the json like so:

{
   "count":4,
   "tasks":[
      "collect paper",
      "do Something else",
      "learn about json",
      "learn about gson"
   ]
}

That way you could simply (de)serialize it with a library like Gson using the following POJO:

public class TaskHolder {

@SerializedName("count")
@Expose
private Integer count;
@SerializedName("tasks")
@Expose
private List<String> tasks = null;

public Integer getCount() {
return count;
}

public void setCount(Integer count) {
this.count = count;
}

public List<String> getTasks() {
return tasks;
}

public void setTasks(List<String> tasks) {
this.tasks = tasks;
}

}

That way it's a lot easier (imho) to manipulate the data and pass it back and forth. Good luck!

Answer 5

Before directly go straightforward understand what is json and how we use in android.

for Json you know there are tow brackets first one is '[ ]' which is display as Json Array and another one is '{ }' which display Json Object, So if you want to parse data from json object then its difficulty if you perfectly understand structure of json data,

Here is the example which will explain you json parsing

String jsonData="{"data":["a","b","c"]}";

Now if you want to access a then just structure, First one is Object so create JSON Object and put string in Argument.

JSONObject json=new JSONObject(jsonData);

Second one is array so you need to put inside as array, JSONObject and JSONArray Object also provide some defual method which will help to parse data,

JSONArray jsonArray=json.getJsonArray(postion); //postion 1 for 'a' String finalData=jsonArray.getString(0);

Now then after try for your code,

Answer 6

JSONObject json = new JSONObject(result);

                    MAX_ROWS = json.getJSONArray("count").getInt(0);
                    System.out.println("rows:" + MAX_ROWS);
                    for (int task_id = 0; task_id < MAX_ROWS; task_id++) {
                        JSONObject task = json.getJSONArray("task" + task_id);
                        taskname[task_id] = task.getString(0);
                        System.out.println(taskname[task_id]);
                    }

Answer 7

Lets consider your json response as a String result, and use following code to parse the json

String result = "{\"count\": [\"4\"],\"tasks0\": [\"collect paper\"],\"tasks1\": [\"krishna\"],\"tasks2\": [\"mys\"],\"tasks3\": [\"bng\"]}";
        JSONObject json = null;
        try {
            json = new JSONObject(result);
            String countString = json.getJSONArray("count").optString(0, "default_value");
            int MAX_ROWS = Integer.parseInt(countString);

            for (int task_id = 0; task_id < MAX_ROWS; task_id++) {
                String taskString = json.getJSONArray("tasks" + task_id).optString(0, "default_value");
                Log.d("Task Names", taskString);
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }

Answer 8

Try this;

if (!result.equals("employee ID doesnt match!!") || !result.equals("post variables are not set")) {
                JSONObject json = new JSONObject(result);

              int  MAX_ROWS = Integer.parseInt(json.getString("count"));
                System.out.println("rows:"+MAX_ROWS);
                String taskname[] = new String[MAX_ROWS];
                JSONArray tasks = json.getJSONArray("tasks");
                for (int task_id = 0; task_id < MAX_ROWS; task_id++) {
                    taskname[task_id] = tasks.getString(task_id);
                    System.out.println(tasks.getString(task_id));
                }

            }