如何從ViewPager獲取當前查看圖像？

Question

我瀏覽過與SO相似的多個主題，但找不到解決方案。我有一個ViewPager的活動。它使用Picasso在ImageView中加載圖像。它工作正常，併成功加載圖像，我可以通過它們滑動。但問題是我想保存當前的觀看圖像或可繪製的。我可以編碼保存，但爲此，我首先必須得到drawable，而我似乎無法做到這一點。

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); 
     } 
    } 
} 

我一直在使用這種嘗試：

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

這也太：

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

我也曾嘗試getTag和setTag種方式，但我得到的NullPointerException每次我雖然正確設置標籤位置

Answer 1

你的做法是相當奇怪的是誠實的。 ViewPager一次至少創建兩個頁面（這樣您可以在上一頁和下一頁之間平滑滾動），因此您不會以這種方式獲取當前活動頁面。

所以，你簡單的方法是：

添加以下內容到你的適配器類

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

添加此到instantiateItem

views.put(position, imageView)

底部頂部

將此添加到destroyItem的底部

views.remove(position, imageView)

並通過這樣做讓你繪製

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