如代码所示，我在两行中得到一个空指针异常，带有三颗星。请注意。我是android的初学者。提前致谢。我尝试实例化瓦片 JSONarray 但即使这样也行不通。
package pack.assignment; ***
import java.net.URL;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.InputStream;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.widget.Toast;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import java.io.IOException;
import android.widget.ImageView;
import java.net.MalformedURLException;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.app.Activity;
import android.app.ProgressDialog;
public class Landing extends Activity {
// url to make request
private static String url = "http://playup-jo.s3.amazonaws.com/dev/config.json";
private ProgressDialog pDialog;
JSONParser jParser = new JSONParser();
// tiles JSONArray
JSONArray tiles=null;
ImageView img;
// JSON Node names
private static final String TAG_TILES = "tiles";
private static final String TAG_IMAGE = "image";
private static final String TAG_URL = "url";
private static final String TAG_MDPI = "mdpi";
private static final String TAG_NAME = "name";
// Intent go = new Intent(this, Google.class);
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// Loading JSON in Background Thread
new LoadJSON().execute();
img = (ImageView)findViewById(R.id.image);
// getting JSON string from URL
JSONObject json = jParser.getJSONFromUrl(url);
}
/**
* Background Async Task to Load all INBOX messages by making HTTP Request
* */
class LoadJSON extends AsyncTask<String, String, Bitmap> {
/**
* Before starting background thread Show Progress Dialog
* */
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(Landing.this);
pDialog.setMessage("Loading ...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
/**
* getting JSON
* */
protected Bitmap doInBackground(String... args) {
// getting JSON string from URL
JSONObject json = jParser.getJSONFromUrl(url);
Bitmap bitmap=null;
// Check your log cat for JSON reponse
// Log.d("JSONNN: ", json.toString());
try {
// Getting Array of Tiles
tiles= new JSONArray();
tiles = json.getJSONArray(TAG_TILES); ***
// looping through All Tiles
for(int i = 0; i < 1; i++){
JSONObject c = tiles.getJSONObject(i);
// Storing json item in variable
String name = c.getString(TAG_NAME);
// mdpi is again JSONObject
JSONObject mdpi= c.getJSONObject(TAG_MDPI);
String image=mdpi.getString(TAG_IMAGE);
String url=mdpi.getString(TAG_URL);
// Using the variable to get the bitmap
try {
bitmap = BitmapFactory.decodeStream((InputStream)new URL(image).getContent());
}
catch (MalformedURLException e) {
e.printStackTrace();
}
catch (IOException e) {
e.printStackTrace();
}
}
}
catch (JSONException e) {
e.printStackTrace();
}
return bitmap;
}
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(final Bitmap result) {
// dismiss the dialog after getting all products
pDialog.dismiss();
// updating UI from Background Thread
runOnUiThread(new Runnable() {
public void run() {
/**
* Updating parsed JSON data
* */
img.setImageBitmap(result); // Rule:2 Always access UI toolkit for UI thread not worker thread
MyEventHandler myEvHandler = new MyEventHandler();
// making the downloaded image clickable
img.setOnClickListener(myEvHandler);
}
});
}
}
class MyEventHandler implements OnClickListener
{
public void onClick(View v)
{
if (v instanceof ImageView)
{
// startActivity(go);
}
}
}
}