org.json.JSONException：Value＆lt;类型java.lang.String无法转换为JSONArray

Question

这是来自mysql数据库的Json编码：

[
   {"id":"1","title":"test_worked","desc":"the first project","done":"0"},
   {"id":"2","title":"mohsen","desc":"Zikey01","done":"1"},
   {"id":"3","title":"ms","desc":"tl","done":"1"}
]

这是我的代码。但有一个错误org.json.JSONException：Value＆lt;类型java.lang.String无法转换为JSONArray

类ReadJSON扩展了AsyncTask {

protected String doInBackground(String... args) {
    InputStream jsonStream = getStreamFromURL(url1, "GET");
    String jsonString = streamToString(jsonStream);
    if (jsonString!=null){
        try {
            JSONArray tasks = new JSONArray(jsonString);
            for ( int i=0;i<tasks.length();i++){
                JSONObject task =tasks.getJSONObject(i);
                Log.i("myLog1403","array is"+task.getString("desc"));
            }
        } catch (JSONException e) {
            e.printStackTrace();
            Log.i("my-Log","cant use json Array");
        }
    }






    return null;
}

}

<?php
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "note_db";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
} 

$sql = "SELECT * from task";
$result = $conn->query($sql);
$Output = array();

if ($result->num_rows > 0) {
    // output data of each row
    while($row = $result->fetch_assoc()) {
		$record=array();
          $record['id']=$row['task_id'];
		    $record['title']=$row['task_title'];
			  $record['desc']=$row['task_desc'];
			    $record['done']=$row['task_done'];
				
				$output[]=$record;
    }
echo	json_encode($output);
} else {
    echo "0 results";
}
$conn->close();
?>