I am getting this NullPointerException from the code that I got online for plotting a line graph using JSON.problem is I am an absolute beginner to android and I couldn't fix it please help. the code is as follow
JSON file
{
"id": 1,
"coffee": [
{
"Date": "18:25:43",
"Estimate": 25.4
},
{
"Date": "18:35:43",
"Estimate": 27.3
},
{
"Date": "18:45:21",
"Estimate": 26.3
},
{
"Date": "18:55:43",
"Estimate": 25.2
}
]
}
AppController.java file
public class AppController extends Application {
public static final String TAG = AppController.class.getSimpleName();
private RequestQueue mRequestQueue;
private static AppController mInstance;
@Override
public void onCreate() {
super.onCreate();
mInstance = this;
}
public static synchronized AppController getInstance() {
return mInstance;
}
public RequestQueue getRequestQueue() {
if (mRequestQueue == null) {
mRequestQueue = Volley.newRequestQueue(getApplicationContext());
}
return mRequestQueue;
}
public <T> void addToRequestQueue(Request<T> req, String tag) {
req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
getRequestQueue().add(req);
}
}
MainActivity.java file
public class MainActivity extends AppCompatActivity {
Button button;
ArrayList<Entry> x;
ArrayList<String> y;
private LineChart mChart;
public String TAG = "AppController";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button=(Button)findViewById(R.id.click);
x = new ArrayList<Entry>();
y = new ArrayList<String>();
mChart = (LineChart)findViewById(R.id.chart1);
mChart.setDrawGridBackground(false);
mChart.setDescription("");
mChart.setTouchEnabled(true);
mChart.setDragEnabled(true);
mChart.setScaleEnabled(true);
mChart.setPinchZoom(true);
//mChart.setMarkerView(mv);
XAxis xl = mChart.getXAxis();
xl.setAvoidFirstLastClipping(true);
YAxis leftAxis = mChart.getAxisLeft();
leftAxis.setInverted(true);
YAxis rightAxis = mChart.getAxisRight();
rightAxis.setEnabled(false);
Legend l = mChart.getLegend();
l.setForm(Legend.LegendForm.LINE);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
drawChart();
}
});
}
private void drawChart() {
String tag_string_req = "req_chart";
StringRequest strReq = new StringRequest(Request.Method.POST, "https://api.myjson.com/bins/10w5bk",
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
Log.d(TAG, "Response: " + response);
try {
JSONObject jsonObject = new JSONObject(response);
String id = jsonObject.getString("id");
JSONArray jsonArray = jsonObject.getJSONArray("coffee");
for (int i = 0; i < jsonArray.length(); i++) {
/* int value = jsonObject.getInt("value");
String date = jsonObject.getString("time");*/
int Estimate = jsonObject.getInt("Estimate");
String Date = jsonObject.getString("Date");
x.add(new Entry(Estimate, i));
y.add(Date);
}
LineDataSet set1 = new LineDataSet(x, "NAV Data Value");
set1.setLineWidth(1.5f);
set1.setCircleRadius(4f);
LineData data = new LineData(y, set1);
mChart.setData(data);
mChart.invalidate();
}
catch (Exception e) {
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Log.e(TAG, "Error: " + error.getMessage());
}
});
strReq.setRetryPolicy(new RetryPolicy() {
@Override
public void retry(VolleyError arg0) throws VolleyError {
}
@Override
public int getCurrentTimeout() {
return 0;
}
@Override
public int getCurrentRetryCount() {
return 0;
}
});
strReq.setShouldCache(false);
AppController.getInstance().addToRequestQueue(strReq, tag_string_req);
}
}
activity_mmain.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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">
<com.github.mikephil.charting.charts.LineChart
android:id="@+id/chart1"
android:layout_width="match_parent"
android:layout_height="484dp" />
<Button
android:id="@+id/click"
android:layout_below="@+id/chart1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
</RelativeLayout>
the Error Logcat message
Process: com.example.stackoverflowtry, PID: 32279 java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.stackoverflowtry.AppController.addToRequestQueue(com.android.volley.Request, java.lang.String)' on a null object reference at com.example.stackoverflowtry.MainActivity.drawChart(MainActivity.java:139) at com.example.stackoverflowtry.MainActivity.access$000(MainActivity.java:30) at com.example.stackoverflowtry.MainActivity$1.onClick(MainActivity.java:66)
