force close when assign onclick to button

I am very new in android development as well as in Java. I had developed an application that gets an image url from a site and wanted to download it into the device and later on I would like to enable users to set it as wallpapers. however, I am met a problem when assigning onclick event to a button.

Once I uncomment the line in red, it will pop up a box stating that the application was stopped unexpectedly. Can someone please help me with this?

private ImageView imView = null;

public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    setContentView(R.layout.main);

    try {
        /* Create a URL we want to load some xml-data from. */
        URL url = new URL(xmlURL);
        /* Get a SAXParser from the SAXPArserFactory. */
        SAXParserFactory spf = SAXParserFactory.newInstance();
        SAXParser sp = spf.newSAXParser();

        /* Get the XMLReader of the SAXParser we created. */
        XMLReader xr = sp.getXMLReader();
        /* Create a new ContentHandler and apply it to the XML-Reader */
        ExampleHandler myExampleHandler = new ExampleHandler();
        xr.setContentHandler(myExampleHandler);

        /* Parse the xml-data from our URL. */
        xr.parse(new InputSource(url.openStream()));
        /* Parsing has finished. */

        /* Our ExampleHandler now provides the parsed data to us. */
        ParsedExampleDataSet parsedExampleDataSet = myExampleHandler.getParsedData();

        /* Set the result to be displayed in our GUI. */
        if (myExampleHandler.filenames != null) {
            a = a + "\n" + myExampleHandler.filenames + ", by "
                + myExampleHandler.authors + "\nhits: "
                + myExampleHandler.hits + " downloads";
            this.ed = myExampleHandler.thumbs;
            this.imageURL = myExampleHandler.mediafiles;
        }
    } catch (Exception e) {
        a = e.getMessage();
    }

    // get thumbnail
    Context context = this.getBaseContext();
    if (ed.length() != 0) {
        Drawable image = ImageOperations(context, this.ed, "image.jpg");
        ImageView imgView = new ImageView(context);
        imgView = (ImageView) findViewById(R.id.image1);
        imgView.setImageDrawable(image);
    }

    TextView tv = (TextView) findViewById(R.id.txt_name);
    tv.setText(a);

    Button bt3 = (Button) findViewById(R.id.get_imagebt);
    //bt3.setOnClickListener(getImageBtnOnClick);
}

OnClickListener getImageBtnOnClick = new OnClickListener() {
    public void onClick(View view) {
        downloadFile(imageURL);
    }
};

void downloadFile(String fileUrl) {
    URL myFileUrl = null;
    try {
        myFileUrl = new URL(fileUrl);
    } catch (MalformedURLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
        
    try {
        HttpURLConnection conn = (HttpURLConnection) myFileUrl.openConnection();
        conn.setDoInput(true);
        conn.connect();
        int length = conn.getContentLength();

        InputStream is = conn.getInputStream();

        bmImg = BitmapFactory.decodeStream(is);
        // this.imView.setImageBitmap(bmImg);
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

private Drawable ImageOperations(Context ctx, String url, String saveFilename) {
    try {
        InputStream is = (InputStream) this.fetch(url);
        Drawable d = Drawable.createFromStream(is, "src");
        return d;
    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    return null;
}

public Object fetch(String address) throws MalformedURLException, IOException {
    URL url = new URL(address);
    Object content = url.getContent();
    return content;
}

Main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" 
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" 
    android:id="@+id/viewgroup">

    <ImageView android:id="@+id/image1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center" />

    <ImageView android:id="@+id/image2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center" />

    <TextView android:id="@+id/txt_name"
        android:layout_width="wrap_content" 
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal" />

    <Button id="@+id/get_imagebt"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text=&开发者_如何转开发quot;xxx Get an image"
        android:layout_gravity="center" />  

    <ImageView id="@+id/imview"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center" /> 
</LinearLayout>

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Please, check catlog view for an error messages. If it's nullPointerException then maybe button of id "get_imagebt" is not a part of a file that you set as a content view? Could you also post your main.xml layout file?
Regards!

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The code you posted does not show the downloadFile() function; it would help if you paste it too. Also, can you specify the exception that you are getting(check logcat)?

A problem, that I can think of, could be missing INTERNET permission in your manifest file.