Issue
I want to know why my Arraylist does not display anything:
{"Friends":[{"name":"Java","age":"18"},{"name":"Python","age":"35"},{"name":"Denis","age":"45"}]}
MainActivity (toast in catch of OnPostExecute appears, named "CATCH OF THE TRY"):
package com.example.parsingjson;
import androidx.appcompat.app.AppCompatActivity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.Toast;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
public class MainActivity extends AppCompatActivity {
private ListView lv;
String Friends;
String namey, age;
private static String JSON_URL="https://run.mocky.io/v3/9c0d17c6-c9a4-41d9-89cc-ac43e44f2b88";
ArrayList<HashMap<String,String>> friendsList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
friendsList = new ArrayList<>();
lv = findViewById(R.id.listview);
GetData getData = new GetData();
getData.execute();
}
public class GetData extends AsyncTask<String, String, String>{
@Override
protected String doInBackground(String... strings) {
String current = "";
try {
URL url;
HttpURLConnection urlConnection = null;
try {
url = new URL(JSON_URL);
urlConnection = (HttpURLConnection) url.openConnection();
InputStream in = urlConnection.getInputStream();
InputStreamReader isr = new InputStreamReader(in);
int data = isr.read();
while (data != -1) {
current += (char) data;
data = isr.read();
}
return current;
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
}
} catch (Exception e) {
e.printStackTrace();
}
return current;
}
@Override
protected void onPostExecute(String s) {
// Toast.makeText(getApplicationContext(), "POST EXECUTE", Toast.LENGTH_LONG).show();
try{
// Toast.makeText(getApplicationContext(), "TRY", Toast.LENGTH_LONG).show();
JSONObject jsonObject = new JSONObject(s);
JSONArray jsonArray = jsonObject.getJSONArray(Friends);
for (int i = 0; i< jsonArray.length() ; i++){
Toast.makeText(getApplicationContext(), "FOR", Toast.LENGTH_LONG).show();
JSONObject jsonObject1 = jsonArray.getJSONObject(i);
namey = jsonObject1.getString("name");
age = jsonObject1.getString("age");
//HashMap
HashMap<String, String> friends = new HashMap<>();
friends.put("name","namey");
friends.put("age","age");
friendsList.add(friends);
// Toast.makeText(getApplicationContext(), "OPERATION SUCCESSFUL", Toast.LENGTH_LONG).show();
}
// Toast.makeText(getApplicationContext(), "APRES FOR", Toast.LENGTH_LONG).show();
} catch (JSONException e) {
e.printStackTrace();
Toast.makeText(getApplicationContext(), "CATCH OF THE TRY", Toast.LENGTH_LONG).show();
}
// Displaying the results
ListAdapter adapter = new SimpleAdapter(
MainActivity.this,
friendsList,
R.layout.row_layout,
new String[]{"name", "age"},
new int []{R.id.textView, R.id.textView2});
lv.setAdapter(adapter);
}
}
}
row_layout.xml:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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="wrap_content">
<TextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginTop="16dp"
android:fontFamily="sans-serif-black"
android:text="TextView"
android:textColor="#000000"
android:textSize="36sp"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<TextView
android:id="@+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginEnd="24dp"
android:text="TextView"
android:textSize="30sp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toBottomOf="@+id/textView" />
</androidx.constraintlayout.widget.ConstraintLayout>
Activity_Main.xml:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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=".MainActivity">
<ListView
android:id="@+id/listview"
android:layout_width="409dp"
android:layout_height="729dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
Only toast I’m not able to show is located in for (int i = .... Toast in catch is showing.
org.json.JSONException: No value for null
at org.json.JSONObject.get(JSONObject.java:399)
at org.json.JSONObject.getJSONArray(JSONObject.java:594)
at com.example.parsingjson.MainActivity$GetData.onPostExecute(MainActivity.java:107)
at com.example.parsingjson.MainActivity$GetData.onPostExecute(MainActivity.java:52)
at android.os.AsyncTask.finish(AsyncTask.java:755)
at android.os.AsyncTask.access$900(AsyncTask.java:192)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:772)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
@ cactustictacs Thanks to your answer, i discovered that i had forgoten to put the name Friend between the "". Now, the new problem is that i display 3 times NAMEY and AGE instead of Java 18, Python 35 and Denis 45. Do you have any idea? EDIT: I had put the String namey and age between "", it’s why i displayed 3 times namey and age. THANK YOU VERY MUCH
Solution
Here’s the bit in your stacktrace that says where it’s going wrong:
org.json.JSONException: No value for null
at org.json.JSONObject.get(JSONObject.java:399)
at org.json.JSONObject.getJSONArray(JSONObject.java:594)
at com.example.parsingjson.MainActivity$GetData.onPostExecute(MainActivity.java:107)
So at line 107 in MainActivity, in your onPostExecute function, you’re calling getJSONArray(). The exception is no value for null which implies you’re passing null to that call.
I don’t know which is line 107 specifically, but I’m assuming it’s this:
JSONArray jsonArray = jsonObject.getJSONArray(Friends);
and if you’re passing null into that, then Friends must be null. And from the code you’ve posted, that’s true – you create the variable
// no value assigned - null by default
String Friends;
but then you don’t actually assign a String to it anywhere. I’m guessing you meant to assign the JSON key to it
String Friends = "Friends";
Also the variable name should really be friends – only classes and interfaces should start with a capital letter. Just makes it easier to tell what’s happening!
Answered By – cactustictacs
Answer Checked By – Mary Flores (FlutterFixes Volunteer)