Before I go into detail about the troubles that I have been having, let me explain that I am pretty new to android development and I will explain what I am trying to achieve, where I am at so far and the problem that I have encountered.
I am developing an android app in version 4.0 using eclipse and what I would like to create is a login page with a username and password which is inputted by a user then checked by an external database to validate and display an alert saying whether the login is successful or not. If it is successful, the app will load a new page with an image obtained from a web source such as this: http://community.dur.ac.uk/cs.seg05/Wild/CameraImages/IMG_0364.JPG being displayed on the page. There will be some more information displayed around this page to help a user classify what is in the image and once the user is finished with this image, they would press a button (i have not put this in yet) and a new image would pop up and the process repeats.
So far, I have managed to get the login page working and I can load up a new page/activity fine with text and default widgets etc and using default images supplied by the android project. However, the problem comes when I am trying to access an image from a url and place it in an image viewer.
I have read and tried about 7-10 different implementations on how to do this (https://stackoverflow.com/questions/17495970/image-view-null-pointer-exception,https://stackoverflow.com/questions/4417552/null-pointer-exception-when-drawing-an-image, Null pointer exception when getting image from url to put in imageview, How to load an ImageView by URL in Android?, https://www.youtube.com/watch?v=KmYJBhz1gmk are just some examples ) but every single one I have tried returns the following error message in LogCat which then crashes the app, regardless of what url it is and what type the image is (jpg, png etc):
Nb com.example.hello is the package name (it was just what was there when i created the project)
Fatal Exception: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.hello/com.example.hello.SecondActivity}: java.lang.NullPointerException
at android.app.Activity.ActivityThread.performLaunchActivity(ActivityThread.java:1955)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4340)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invokeNative(Method.java:511)
at com.android.internal.os.ZygotInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
at com.android.internal.os.ZygotInit.main(ZygoteInit.java:551)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
(there is sometimes an extra error line here depending on what implementation I tried)
at com.example.hello.SecondActivity.onCreate(SecondActivity.java:58)
at android.app.Activity.performCreate(Activity.java:4465)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1919)
... 11 more
Now I don't think that Internet permissions is a problem as i have had to do some internet access with some php files prior to encountering this problem and they all work and i also have the user permission in the android manifest xml file which you will see further down on this post. Additionally, I do not think its a url problem as i have tried the url's out in my browser and they are all fine.
So what I ask is this:
What is causing this problem?
What is the approach for tackling the problem (step by step would be useful) and the best implementation to use with what I have described that I want to achieve? (some code would be very helpful)
Do I need to post some more information on here?
Can anyone help
Thanks
P.S Here is the code that I have in my "SecondActivity" which works without the url stuff in (note that the getImages method works fine for something that I need for the future once this issue solved)
package com.example.hello;
import android.app.Activity;
import android.app.ActionBar;
import android.app.Fragment;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.os.Build;
import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URI;
import java.net.URL;
import java.net.URLConnection;
import java.util.*;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONObject;
public class SecondActivity extends Activity {
private String userId; //global variable as it will be used throughout this activity
private ArrayList <String> imageNames;
private int imageNumber=0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
Bundle data = getIntent().getExtras(); //obtains information passed from the previous activity
userId= data.getString("userId"); //gets the user id from the main activity
System.err.println("Received User id " +userId);
if (savedInstanceState == null) {
getFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}
imageNames =getImages(userId); //gets all of the image names from the database
System.err.println(imageNames);
ImageView iv= (ImageView)findViewById(R.id.imageView1); //gets the image view
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.second, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_second,
container, false);
return rootView;
}
}
public ArrayList<String> getImages(String userid) {
ArrayList<String> images= new ArrayList<String>();
try {
HttpClient httpclient= new DefaultHttpClient();
URI website= new URI("https://community.dur.ac.uk/cs.seg05/androidapp/ImageAccess.php?userid="+userid);
HttpGet request= new HttpGet();
request.setURI(website);
HttpResponse response = httpclient.execute(request);
BufferedReader reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
StringBuffer sb=new StringBuffer("");
String l= "";
String nl= System.getProperty("line.separator");
while ((l = reader.readLine()) != null) { //converts the whole output into a string
sb.append(l+ nl);
}
reader.close();
String result=sb.toString();
//System.err.println(result);
JSONArray jArray = new JSONArray(result);
System.err.println(jArray);
for(int i=0;i<jArray.length();i++){ //retrieves the JSon
JSONObject json_data = jArray.getJSONObject(i);
images.add(json_data.getString("File_Name"));
}
}
catch (Exception e) {
}
return images;
}
}
Here is the xml with imageview contained that the activity is mapped to:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.hello.SecondActivity$PlaceholderFragment" >
<ImageView
android:id="@+id/imageView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_centerVertical="true"
android:layout_marginLeft="144dp" />
</RelativeLayout>
Here is the xml for my Android manifest:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.hello"
android:versionCode="1"
android:versionName="1.0" >
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-sdk
android:minSdkVersion="14"
android:targetSdkVersion="14" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.hello.MainActivity" //login activity
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="com.example.hello.SecondActivity"
android:label="@string/app_name" >
</activity>
</application>
Hope that this is enough information. If not, let me know and I will post it
Here is an example of what i have tried
Bitmap bm= getBitmapFromURL("http://community.dur.ac.uk/cs.seg05/Wild/CameraImages/1");
ImageView iv= (ImageView)findViewById(R.id.imageView1); //gets the image view
iv.setImageBitmap(bm); //this is line 58 in this example
where the getBitmapFromURL is this method
public static Bitmap getBitmapFromURL(String src) {
try {
java.net.URL url = new java.net.URL(src);
HttpURLConnection connection = (HttpURLConnection) url
.openConnection();
connection.setDoInput(true);
connection.connect();
InputStream input = connection.getInputStream();
Bitmap myBitmap = BitmapFactory.decodeStream(input);
return myBitmap;
} catch (IOException e) {
e.printStackTrace();
return null;
}
}
