Android : Initialize XML object from programmatically which has parameter

Question

I have a class called CoverFlowClass. I used to do this to create a class,

CoverFlowClass coverFlow = new CoverFlowClass(this)
coverFlow.setAdapter(new ImageAdapter(this));

But now I want to use XML so I can do layouting. I create an XML code like this:

<id.co.ajsmsig.display.CoverFlowClass
    android:id="@+id/coverflow"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
/>

But when I create from the code like this :

CoverFlowClass coverFlow=  (CoverFlowClass) findViewById(R.id.coverflow);
coverFlow.setAdapter(new ImageAdapter(this));

My app force closed. The error log in LogCat i found is :

04-18 07:46:34.804: E/AndroidRuntime(1847): at id.co.ajsmsig.display.CoverFlowMain.onCreate(CoverFlowMain.java:76).

And the line 76 is :

coverFlow.setAdapter(new ImageAdapter(this));

I think because the class is using a parameter in it constructor (= new CoverFlowClass(this)) while findViewById does not give any parameter. I still have no idea, how to make this work? Any idea is appreciated.

Thanks

P.s. Below is the CoverFlow class source code:

---

package id.co.ajsmsig.display;


import android.content.Context;
import android.graphics.Camera;
import android.graphics.Matrix;
import android.util.AttributeSet;
import android.view.View;
import android.view.animation.Transformation;
import android.widget.Gallery;
import android.widget.ImageView;

public class CoverFlowClass extends Gallery {

    /**
     * Graphics Camera used for transforming the matrix of ImageViews
     */
    private Camera mCamera = new Camera();

    /**
     * The maximum angle the Child ImageView will be rotated by
     */    
    private int mMaxRotationAngle = 60;

    /**
     * The maximum zoom on the centre Child
     */
    private int mMaxZoom = -120;

    /**
     * The Centre of the Coverflow 
     */   
    private int mCoveflowCenter;

    public CoverFlowClass(Context context) {
  super(context);
  this.setStaticTransformationsEnabled(true);
 }

    public CoverFlowClass(Context context, AttributeSet attrs) {
  super(context, attrs);
        this.setStaticTransformationsEnabled(true);
 }

    public CoverFlowClass(Context context, AttributeSet attrs, int defStyle) {
   super(context, attrs, defStyle);
   this.setStaticTransformationsEnabled(true);   
  }

    /**
     * Get the max rotational angle of the image
  * @return the mMaxRotationAngle
  */
    public int getMaxRotationAngle() {
  return mMaxRotationAngle;
 }

 /**
    * Set the max rotational angle of each image
  * @param maxRotationAngle the mMaxRotationAngle to set
  */
    public void setMaxRotationAngle(int maxRotationAngle) {
  mMaxRotationAngle = maxRotationAngle;
 }

 /**
    * Get the Max zoom of the centre image
  * @return the mMaxZoom
  */
    public int getMaxZoom() {
  return mMaxZoom;
 }

 /**
    * Set the max zoom of the centre image
  * @param maxZoom the mMaxZoom to set
  */
    public void setMaxZoom(int maxZoom) {
        mMaxZoom = maxZoom;
    }

 /**
     * Get the Centre of the Coverflow
     * @return The centre of this Coverflow.
     */
    private int getCenterOfCoverflow() {
        return (getWidth() - getPaddingLeft() - getPaddingRight()) / 2 + getPaddingLeft();
    }

    /**
     * Get the Centre of the View
     * @return The centre of the given view.
     */
    private static int getCenterOfView(View view) {
        return view.getLeft() + view.getWidth() / 2;
    }  
    /**
     * {@inheritDoc}
  *
  * @see #setStaticTransformationsEnabled(boolean) 
  */ 
    protected boolean getChildStaticTransformation(View child, Transformation t) {

  final int childCenter = getCenterOfView(child);
  final int childWidth = child.getWidth() ;
  int rotationAngle = 0;

  t.clear();
  t.setTransformationType(Transformation.TYPE_MATRIX);

        if (childCenter == mCoveflowCenter) {
            transformImageBitmap((ImageView) child, t, 0);
        } else {      
            rotationAngle = (int) (((float) (mCoveflowCenter - childCenter)/ childWidth) *  mMaxRotationAngle);
            if (Math.abs(rotationAngle) > mMaxRotationAngle) {
             rotationAngle = (rotationAngle < 0) ? -mMaxRotationAngle : mMaxRotationAngle;   
            }
            transformImageBitmap((ImageView) child, t, rotationAngle);         
        }    

  return true;
 }

 /**
    * This is called during layout when the size of this view has changed. If
  * you were just added to the view hierarchy, you're called with the old
  * values of 0.
  *
  * @param w Current width of this view.
  * @param h Current height of this view.
  * @param oldw Old width of this view.
  * @param oldh Old height of this view.
     */
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        mCoveflowCenter = getCenterOfCoverflow();
        super.onSizeChanged(w, h, oldw, oldh);
     }

    /**
    * Transform the Image Bitmap by the Angle passed 
    * 
    * @param imageView ImageView the ImageView whose bitmap we want to rotate
    * @param t transformation 
    * @param rotationAngle the Angle by which to rotate the Bitmap
    */
    private void transformImageBitmap(View child, Transformation t, int rotationAngle) {            
      mCamera.save();
      final Matrix imageMatrix = t.getMatrix();;
      final int imageHeight = child.getLayoutParams().height;;
      final int imageWidth = child.getLayoutParams().width;
      final int rotation = Math.abs(rotationAngle);

      mCamera.translate(0.0f, 0.0f, 100.0f);

      //As the angle of the view gets less, zoom in     
      if ( rotation < mMaxRotationAngle ) {
       float zoomAmount = (float) (mMaxZoom +  (rotation * 1.5));
       mCamera.translate(0.0f, 0.0f, zoomAmount);          
      } 

      mCamera.rotateY(rotationAngle);
      mCamera.getMatrix(imageMatrix);               
      imageMatrix.preTranslate(-(imageWidth/2), -(imageHeight/2)); 
      imageMatrix.postTranslate((imageWidth/2), (imageHeight/2));
      mCamera.restore();
 }
}

Answer 1

It sounds like you have a NullPointerException: the findViewById call does not actually find the View, because it is never instantiated. You probably need to implement a constructor for CoverFlowClass that takes in an `AttributeSet. Perhaps like so:

public CoverFlowClass(Context context, AttributeSet attrs) 
{
    super(context, attrs);

        // do whatever other initialization is necessary
}

Answer 2

Sorry this response is a bit late, but maybe it will help someone out there with similar problems. It also think this sounds like a NullPointerException, so if you intend to use the Coverflow in an XML layout, be sure to setContentView(R.layout.main) before you call any findViewById. you can println the value of coverFlow to make sure it is no longer null.