Hi I am learning Android App Development. For this, I wanted to make myself a simple wallpaper app. Hence, I wrote something roughly which is presented here. I want to get wallpaper urls from json. Unfortunately, I am unable to get data from my server. java.lang.NullPointerException: Attempt to read from null array
How do I get the data correctly from the jsonParse asynctask?
I am stuck on this the whole day. What could have gone wrong here?
Here is my code:
myjson.json:
{
"walls":[
{"ourUrl":"http://www.hdbloggers.net/wp-content/uploads/2016/01/Wallpapers-for-Android.jpg"},
{"ourUrl":"http://androidwallpape.rs/content/02-wallpapers/131-night-sky/wallpaper-2707591.jpg"},
{"ourUrl":"http://androidwallpape.rs/content/02-wallpapers/155-starrynight/starry-night-sky-star-galaxy-space-dark-9-wallpaper.jpg"}
]
}
MainActivity.java:
package regalstreak.me.wallpapers;
import android.app.Activity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
public class MainActivity extends Activity {
RecyclerView recyclerView;
RecyclerView.LayoutManager layoutManager;
RecyclerView.Adapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = (RecyclerView)findViewById(R.id.recycler_view);
layoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(layoutManager);
adapter = new RecyclerAdapter(this);
recyclerView.setAdapter(adapter);
}
}
RecyclerAdapter.java:
package regalstreak.me.wallpapers;
import android.content.Context;
import android.os.AsyncTask;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import org.apache.commons.io.IOUtils;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.util.ArrayList;
import java.util.List;
// This is a recycleradapter which will set the correct images to the correct position in the recyclerview.
public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.ViewHolder> {
private Context myCtx1;
String[] arr;
String[] arrurl;
String jsonURL = "http://dev.regalstreak.me/myjson.json";
public RecyclerAdapter(Context ctx) {
this.myCtx1 = ctx;
}
public ImageView Image;
private String[] mText = {
"Text 1",
"Text 2",
"Text 3"
};
public class ViewHolder extends RecyclerView.ViewHolder {
public TextView Text;
public ViewHolder(View itemView) {
super(itemView);
Image = (ImageView) itemView.findViewById(R.id.image_view);
Text = (TextView) itemView.findViewById(R.id.text_view);
}
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
View v = LayoutInflater.from(viewGroup.getContext())
.inflate(R.layout.wallpapers_list, viewGroup, false);
ViewHolder viewHolder = new ViewHolder(v);
return viewHolder;
}
@Override
public void onBindViewHolder(ViewHolder viewHolder, int i) {
viewHolder.Text.setText(mText[i]);
new jsonParse().execute();
new DownloadImageTask(Image).execute(arrurl[i]);
}
@Override
public int getItemCount() {
return mText.length;
}
class jsonParse extends AsyncTask<String, Void, String[]> {
protected String[] doInBackground(String[] urls) {
String myText = null;
String url = urls[0];
String ourUrl;
try {
InputStream in = new java.net.URL(jsonURL).openStream();
myText = IOUtils.toString(in, "utf-8");
in.close();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
try {
// Parse the json
List<String> allUrls = new ArrayList<String>();
JSONObject jsonObjectRoot = new JSONObject(myText);
JSONArray jsonArray = jsonObjectRoot.getJSONArray("walls");
for (int i = 0; i < jsonArray.length(); i++) {
JSONObject jsonObject = jsonArray.getJSONObject(i);
ourUrl = jsonObject.getString("ourUrl");
allUrls.add(ourUrl);
}
arr = allUrls.toArray(new String[allUrls.size()]);
} catch (JSONException e) {
e.printStackTrace();
}
return arr;
}
protected void onPostExecute(String[] result){
arrurl = result;
}
}
}
DownloadImageTask.java:
package regalstreak.me.wallpapers;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.util.Log;
import android.widget.ImageView;
import java.io.InputStream;
// Here, we will download the wallpapers obtained from jsonData with an asynctask.
public class DownloadImageTask extends AsyncTask<String, Void, Bitmap>{
ImageView bmImage;
public DownloadImageTask(ImageView bmImage){
this.bmImage = bmImage;
}
protected Bitmap doInBackground(String... urls) {
String urldisplay = urls[0];
Bitmap mIcon11 = null;
try {
InputStream in = new java.net.URL(urldisplay).openStream();
mIcon11 = BitmapFactory.decodeStream(in);
in.close();
} catch (Exception e) {
Log.e("Error getting images.", e.getMessage());
e.printStackTrace();
}
return mIcon11;
}
protected void onPostExecute(Bitmap result){
bmImage.setImageBitmap(result);
}
}
activity_main.xml:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="regalstreak.me.wallpapers.MainActivity">
<android.support.v7.widget.RecyclerView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/recycler_view" />
</RelativeLayout>
wallpaper_list.xml:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/relative"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingTop="5dp">
<ImageView
android:id="@+id/image_view"
android:layout_width="match_parent"
android:layout_height="150dp" />
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignBottom="@id/image_view"
android:alpha="0.6"
android:background="@color/colorDivider"
android:padding="9dp">
<TextView
android:id="@+id/text_view"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textAlignment="center"
android:textColor="@color/colorPrimaryText" />
</RelativeLayout>
</RelativeLayout>