如何从ViewPager获取当前正在查看的图像？

Question

I have browsed multiple threads on SO with issues similar to mine but couldn't find a resolution. I have an activity which has a ViewPager. It loads an image in ImageView using Picasso. It's working fine and successfully loads the images and I can swipe through them. But the issue is I want to save the current viewing image or drawable. I can code for saving but for that, I first have to get drawable which I can't seem to do.

XML:

<android.support.v4.view.ViewPager
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/view_pager"
    android:background="@color/black"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

SwipeActivity.java

public class SwipeActivity extends AppCompatActivity {

    private ViewPager viewPager;
    private ImageView imageView;


    public void save(){
        int currentItem =viewPager.getCurrentItem();
        Drawable drawable = (Drawable) imageView.getDrawable().getCurrent();
        ImageView am = (ImageView)imageView.getTag(currentItem);
        Log.e("Jatt", "save: "+currentItem );
        //Lots of Confustion here. Don't look at this function
        //I have messed it up. But will correct once I get the way
        Bitmap bm = ((BitmapDrawable)am.getDrawable()).getBitmap();
        //Bitmap bm =((BitmapDrawable) drawable).getBitmap();
        storeImage(bm);
    }

    private  File getOutputMediaFile(){
        // To be safe, you should check that the SDCard is mounted
        // using Environment.getExternalStorageState() before doing this.
        File mediaStorageDir = new File(Environment.getExternalStorageDirectory()
                + "/Android/data/");

        // This location works best if you want the created images to be shared
        // between applications and persist after your app has been uninstalled.

        // Create the storage directory if it does not exist
        if (! mediaStorageDir.exists()){
            if (! mediaStorageDir.mkdirs()){
                return null;
            }
        }
        // Create a media file name
        String timeStamp = new SimpleDateFormat("ddMMyyyy_HHmm").format(new Date());
        File mediaFile;
        String mImageName="MI_"+ timeStamp +".jpg";
        mediaFile = new File(mediaStorageDir.getPath() + File.separator + mImageName);
        return mediaFile;
    }
    private void storeImage(Bitmap image) {
        String TAG="Jatt";
        File pictureFile = getOutputMediaFile();
        if (pictureFile == null) {
            Log.d(TAG,
                    "Error creating media file, check storage permissions: ");// e.getMessage());
            return;
        }
        try {
            FileOutputStream fos = new FileOutputStream(pictureFile);
            image.compress(Bitmap.CompressFormat.PNG, 90, fos);
            fos.close();
        } catch (FileNotFoundException e) {
            Log.d(TAG, "File not found: " + e.getMessage());
        } catch (IOException e) {
            Log.d(TAG, "Error accessing file: " + e.getMessage());
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.saveimage, 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();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            save();
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_swipe);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        setTitle(" ");
        viewPager = (ViewPager) findViewById(R.id.view_pager);
        ImagePagerAdapter adapter = new ImagePagerAdapter();
        viewPager.setAdapter(adapter);
        viewPager.setCurrentItem(getIntent().getIntExtra("pos",0));
    }

    class ImagePagerAdapter extends PagerAdapter {

        @Override
        public int getCount() {
            return Photos.sendToList.length;
        }

        @Override
        public boolean isViewFromObject(View view, Object object) {
            return view == ((ImageView) object);
        }

        @Override
        public Object instantiateItem(ViewGroup container, int position) {
            Context context = SwipeActivity.this;
            imageView = new ImageView(context);
            int padding = context.getResources().getDimensionPixelSize(R.dimen.padding_medium);
            imageView.setPadding(padding, padding, padding, padding);
            imageView.setScaleType(ImageView.ScaleType.CENTER_INSIDE);
            //imageView.setImageResource(Photos.sendToList[position]);
            Picasso.with(context).load(Photos.sendToList[position]).into(imageView);
            ((ViewPager) container).addView(imageView, 0);
            return imageView;
        }

        @Override
        public void destroyItem(ViewGroup container, int position, Object object) {
            ((ViewPager) container).removeView((ImageView) object);
        }
    }
}

I have tried using this:

imageView.getDrawable(); //Return a fixed image no matter which image is 
                         // being currently viewed

and this too:

imageView.getDrawable().getCurrent(); //Doesn't return currently viewing img

I have also tried getTag and setTag kind of way but I get NullPointerException everytime although I set the tag correctly to position

Answer 1

your approach is quite strange to be honest. ViewPager creates two pages at minimum at once (so you can scroll smoothly between previous and next page), thus you won't get currently active page this way.

so, easy approach for you will be:

adding this to your top of your adapter class

HashMap<Integer, ImageView> views = new HashMap();

adding this to the bottom of instantiateItem

views.put(position, imageView)

adding this to the bottom of destroyItem

views.remove(position, imageView)

and getting your drawable by doing

ImagePagerAdapter adapter = ((ImagePagerAdapter) viewPager.getAdapter()); Drawable target = ((ImageView) adapter.views.get(viewPager.getCurrentItem())).getDrawable();