Android Gallery控件-需要无限循环的图像

Question

Without starting from the middle of the stack of images how do I rotate them in the infinite loop left to right and right to left? I tried setSelection(position) but for some reason I get that method called few times and inconsistently. My images increment has to be saved int he app state so it makes it a bit more complicated.

@Override
    public void setSelection(int position){

        int sectionPos = getCurrentPositionFromState();

        if (sectionPos == (this._images - 1)){  
            setCurrentPositionFromState(0);
            sectionPos = 0;
        }
        else {
            setCurrentPositionInState(sectionPos +1);
        }
        if (sectionPos <= (this._images - 1) ){
            super.setSelection(sectionPos);
        }
    }

gallery.setOnItemSelectedListener(new OnItemSelectedListener() {     
            @Override
            public void onItemSelected(AdapterView parent, View view, int position, long id) {

                gallery.setSelection(position);


            @Override
            public void onNothingSelected(AdapterView parent) {


            }
        });

I should also mention that I have an onFling() overriden like so:

@Override
       public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
         return super.onFling(e1, e2, 0, velocityY);
       }

Answer 1

There are a few ways to go about it, but in all cases, it's never technically "infinite." I got the basis of mine from snooping around for a while.

First we need to put a gallery into the xml file in the layout. So after creating the file put in a little snippet like this:

<!-- Gallery To show images Gallery  --> 
< Gallery
    android:id="@+id/galleryView"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:paddingBottom="15dip"/>

Now lets set up a Vector of different images so we can loop through. We will be getting these images from our resources, but if you want to get them from somewhere else then just insert that instead. We are going to insert this into onCreate(). This will allow us to have a vector of id's that we can reference when getting images to put into the gallery later:

public Vector<Integer> mPhotoVector = new Vector<Integer>();

public void setPhotos() {
    for(as many photos as you want){
        int imageResource = getResources().getIdentifier("imageNAme", "drawable", getPackageName());
        mPhotoVector.add(imageResource);
    }

Where galView is my gallery view from the layout. And as we finish up this project we need to call the gallery view from the xml and initialize it to a gallery variable we will have in the code.

LoopingGalleryAdapter adapter;
Gallery galView;

adapter = new LoopingGalleryAdapter(this, mPhotoVector);
galView = (LoopingGallery)mLayoutView.findViewById(R.id.galleryView);
galView.setAdapter(adapter);
galView.setSelection((galView.getCount() / 2));

The setSelection() will have us looking at the middle of the gallery, this makes it appear to be "infinite" since there are now 1073741823 elements to each side.

Next we need to create the adapter. The basis is to make the largest gallery you can, so next we just add in our own little getCount method. This will create a gallery that is too large for the user to (plausibly) scroll to the end of.

Lastly on the adapter we have the meat of the project which requires us to set where our position is. This is the key. Once the position is set to the middle-ish of the gallery, it seems as though you have an infinite loop of images on either side.

I started mine off a little like this:

public class LoopingGalleryAdapter extends BaseAdapter {

     private ImageView iv;
     private Context mContext;
     public PhotoVector mPhotoVector = null;
     int mGalleryItemBackground;

      public LoopingGalleryAdapter(Context c, PhotoVector aVector) {
          this.mContext = c;
          mPhotoVector = aVector;
      }

      public int getCount() {
        return Integer.MAX_VALUE;
      }

      @Override
      public Object getItem(int position) {
          return position;
      }

      public ImageView getImage(){
        return iv;
      }

      @Override
      public long getItemId(int position) {
          return position;
      }

      @Override
      public View getView(int position, View convertView, ViewGroup parent) {
          iv = new ImageView(mContext);
          private final int middle = 1073741823; //this is the middle index of the gallery in galView 

          /************************************************************************
          *if you have a vector/array/arrayList of photos you would like to display
          ************************************************************************/
          if((position - middle) >= 0) { relativePosition = (position-middle) % mPhotoVector.size(); }
          else { relativePosition = mPhotoVector.size() - (Math.abs(position - middle) % mPhotoVector.size()); }

          Drawable draw = mContext.getResources().getDrawable(mPhotoVector.get(relativePosistion));

          /*********************************************
          *otherwise you can just insert a photo like so
          *********************************************/
          Drawable draw = mContext.getResources().getDrawable(R.drawable.what_you_want);

          iv.setImageDrawable(draw);
          return iv;
      }
}

And we are now done!

Additionally, one of the tricks I have found quite useful, if not necessary when getting images from the internet is to keep a count of how many times you have gone through getView() and after 10-20 times clear your cache so you don't throw a OutOfMemoryError by doing:

   if(counter >= 20){
       galView.destroyDrawingCache();
       counter = 0;
   }

Or have getView() throw a OutOfMemoryError , catch it and return an empty ImageView (iv) and then clear then call galView.destroyDrawingCache();

Answer 2

A shameless self plug, just wrote an Infinite Scrolling Gallery tutorial:

http://blog.blundellapps.com/infinite-scrolling-gallery/

Source code can be downloaded also, you choose the image size.

You can use images on your SD card or images in your /resources/drawable directory.