Question

我在ViewPager中顺利滑动有问题。我的目标是使用Volley Library从URL下载图像，并且必须在ViewPager中显示下载的图像，在从左到右或从右到左滑动时没有任何滞后问题。我附加了在扫描图像时滞后的代码。

这是我的Activity类，其中包含view pager：

ViewPagerActivity.java

public class ViewPagerActivity extends Activity {
ViewPager pager;
String[] URL;
PagerAdapter objPagerAdapter;
ArrayList<String> _arrayImagePath=new ArrayList<String>();


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_view_pager);
    pager=(ViewPager)findViewById(R.id.pagerView);

    // Setting the 70 images URL 
    URL= new String[] { "http://vignette3.wikia.nocookie.net/dragonball/images/7/71/PollutionAura2.png/revision/latest?cb=20101211235024",
            "http://vignette2.wikia.nocookie.net/aread/images/6/6f/V02_Back.jpg/revision/latest?cb=20140501154842", 
            "http://vignette1.wikia.nocookie.net/tmnt/images/d/d5/Tnmt-disneyscreencaps_com-5817.jpg/revision/latest?cb=20130428155629",
            "https://upload.wikimedia.org/wikipedia/commons/2/27/Sunset_at_Selsey_beach_4.jpg",
            "http://img1.wikia.nocookie.net/__cb20140806200752/disney/images/d/d8/Little-mermaid-1080p-disneyscreencaps.com-782.jpg",
            "http://img3.wikia.nocookie.net/__cb20141022183927/howtotrainyourdragon/images/c/c5/When_gothi_drops_that_flag_we_race.jpg",
            "http://img.gawkerassets.com/img/17jy4w1lonvyijpg/original.jpg",
            "http://vignette3.wikia.nocookie.net/dragonball/images/7/71/PollutionAura2.png/revision/latest?cb=20101211235024",
            "http://vignette2.wikia.nocookie.net/aread/images/6/6f/V02_Back.jpg/revision/latest?cb=20140501154842", 
            "http://vignette1.wikia.nocookie.net/tmnt/images/d/d5/Tnmt-disneyscreencaps_com-5817.jpg/revision/latest?cb=20130428155629",
            "https://upload.wikimedia.org/wikipedia/commons/2/27/Sunset_at_Selsey_beach_4.jpg",
            "http://img1.wikia.nocookie.net/__cb20140806200752/disney/images/d/d8/Little-mermaid-1080p-disneyscreencaps.com-782.jpg",
            "http://img3.wikia.nocookie.net/__cb20141022183927/howtotrainyourdragon/images/c/c5/When_gothi_drops_that_flag_we_race.jpg",
            "http://img.gawkerassets.com/img/17jy4w1lonvyijpg/original.jpg",
            "http://vignette3.wikia.nocookie.net/dragonball/images/7/71/PollutionAura2.png/revision/latest?cb=20101211235024",
            "http://vignette2.wikia.nocookie.net/aread/images/6/6f/V02_Back.jpg/revision/latest?cb=20140501154842", 
            "http://vignette1.wikia.nocookie.net/tmnt/images/d/d5/Tnmt-disneyscreencaps_com-5817.jpg/revision/latest?cb=20130428155629",
            "https://upload.wikimedia.org/wikipedia/commons/2/27/Sunset_at_Selsey_beach_4.jpg",
            "http://img1.wikia.nocookie.net/__cb20140806200752/disney/images/d/d8/Little-mermaid-1080p-disneyscreencaps.com-782.jpg",
            "http://img3.wikia.nocookie.net/__cb20141022183927/howtotrainyourdragon/images/c/c5/When_gothi_drops_that_flag_we_race.jpg",
            "http://img.gawkerassets.com/img/17jy4w1lonvyijpg/original.jpg",
            "http://vignette3.wikia.nocookie.net/dragonball/images/7/71/PollutionAura2.png/revision/latest?cb=20101211235024",
            "http://vignette2.wikia.nocookie.net/aread/images/6/6f/V02_Back.jpg/revision/latest?cb=20140501154842", 
            "http://vignette1.wikia.nocookie.net/tmnt/images/d/d5/Tnmt-disneyscreencaps_com-5817.jpg/revision/latest?cb=20130428155629",
            "https://upload.wikimedia.org/wikipedia/commons/2/27/Sunset_at_Selsey_beach_4.jpg",
            "http://img1.wikia.nocookie.net/__cb20140806200752/disney/images/d/d8/Little-mermaid-1080p-disneyscreencaps.com-782.jpg",
            "http://img3.wikia.nocookie.net/__cb20141022183927/howtotrainyourdragon/images/c/c5/When_gothi_drops_that_flag_we_race.jpg",
            "http://img.gawkerassets.com/img/17jy4w1lonvyijpg/original.jpg",
            "http://vignette3.wikia.nocookie.net/dragonball/images/7/71/PollutionAura2.png/revision/latest?cb=20101211235024",
            "http://vignette2.wikia.nocookie.net/aread/images/6/6f/V02_Back.jpg/revision/latest?cb=20140501154842", 
            "http://vignette1.wikia.nocookie.net/tmnt/images/d/d5/Tnmt-disneyscreencaps_com-5817.jpg/revision/latest?cb=20130428155629",
            "https://upload.wikimedia.org/wikipedia/commons/2/27/Sunset_at_Selsey_beach_4.jpg",
            "http://img1.wikia.nocookie.net/__cb20140806200752/disney/images/d/d8/Little-mermaid-1080p-disneyscreencaps.com-782.jpg",
            "http://img3.wikia.nocookie.net/__cb20141022183927/howtotrainyourdragon/images/c/c5/When_gothi_drops_that_flag_we_race.jpg",
            "http://img.gawkerassets.com/img/17jy4w1lonvyijpg/original.jpg",
            "http://vignette3.wikia.nocookie.net/dragonball/images/7/71/PollutionAura2.png/revision/latest?cb=20101211235024",
            "http://vignette2.wikia.nocookie.net/aread/images/6/6f/V02_Back.jpg/revision/latest?cb=20140501154842", 
            "http://vignette1.wikia.nocookie.net/tmnt/images/d/d5/Tnmt-disneyscreencaps_com-5817.jpg/revision/latest?cb=20130428155629",
            "https://upload.wikimedia.org/wikipedia/commons/2/27/Sunset_at_Selsey_beach_4.jpg",
            "http://img1.wikia.nocookie.net/__cb20140806200752/disney/images/d/d8/Little-mermaid-1080p-disneyscreencaps.com-782.jpg",
            "http://img3.wikia.nocookie.net/__cb20141022183927/howtotrainyourdragon/images/c/c5/When_gothi_drops_that_flag_we_race.jpg",
            "http://img.gawkerassets.com/img/17jy4w1lonvyijpg/original.jpg",
            "http://vignette3.wikia.nocookie.net/dragonball/images/7/71/PollutionAura2.png/revision/latest?cb=20101211235024",
            "http://vignette2.wikia.nocookie.net/aread/images/6/6f/V02_Back.jpg/revision/latest?cb=20140501154842", 
            "http://vignette1.wikia.nocookie.net/tmnt/images/d/d5/Tnmt-disneyscreencaps_com-5817.jpg/revision/latest?cb=20130428155629",
            "https://upload.wikimedia.org/wikipedia/commons/2/27/Sunset_at_Selsey_beach_4.jpg",
            "http://img1.wikia.nocookie.net/__cb20140806200752/disney/images/d/d8/Little-mermaid-1080p-disneyscreencaps.com-782.jpg",
            "http://img3.wikia.nocookie.net/__cb20141022183927/howtotrainyourdragon/images/c/c5/When_gothi_drops_that_flag_we_race.jpg",
            "http://img.gawkerassets.com/img/17jy4w1lonvyijpg/original.jpg",
            "http://vignette3.wikia.nocookie.net/dragonball/images/7/71/PollutionAura2.png/revision/latest?cb=20101211235024",
            "http://vignette2.wikia.nocookie.net/aread/images/6/6f/V02_Back.jpg/revision/latest?cb=20140501154842", 
            "http://vignette1.wikia.nocookie.net/tmnt/images/d/d5/Tnmt-disneyscreencaps_com-5817.jpg/revision/latest?cb=20130428155629",
            "https://upload.wikimedia.org/wikipedia/commons/2/27/Sunset_at_Selsey_beach_4.jpg",
            "http://img1.wikia.nocookie.net/__cb20140806200752/disney/images/d/d8/Little-mermaid-1080p-disneyscreencaps.com-782.jpg",
            "http://img3.wikia.nocookie.net/__cb20141022183927/howtotrainyourdragon/images/c/c5/When_gothi_drops_that_flag_we_race.jpg",
            "http://img.gawkerassets.com/img/17jy4w1lonvyijpg/original.jpg",
            "http://vignette3.wikia.nocookie.net/dragonball/images/7/71/PollutionAura2.png/revision/latest?cb=20101211235024",
            "http://vignette2.wikia.nocookie.net/aread/images/6/6f/V02_Back.jpg/revision/latest?cb=20140501154842", 
            "http://vignette1.wikia.nocookie.net/tmnt/images/d/d5/Tnmt-disneyscreencaps_com-5817.jpg/revision/latest?cb=20130428155629",
            "https://upload.wikimedia.org/wikipedia/commons/2/27/Sunset_at_Selsey_beach_4.jpg",
            "http://img1.wikia.nocookie.net/__cb20140806200752/disney/images/d/d8/Little-mermaid-1080p-disneyscreencaps.com-782.jpg",
            "http://img3.wikia.nocookie.net/__cb20141022183927/howtotrainyourdragon/images/c/c5/When_gothi_drops_that_flag_we_race.jpg",
            "http://img.gawkerassets.com/img/17jy4w1lonvyijpg/original.jpg",
            "http://vignette3.wikia.nocookie.net/dragonball/images/7/71/PollutionAura2.png/revision/latest?cb=20101211235024",
            "http://vignette2.wikia.nocookie.net/aread/images/6/6f/V02_Back.jpg/revision/latest?cb=20140501154842", 
            "http://vignette1.wikia.nocookie.net/tmnt/images/d/d5/Tnmt-disneyscreencaps_com-5817.jpg/revision/latest?cb=20130428155629",
            "https://upload.wikimedia.org/wikipedia/commons/2/27/Sunset_at_Selsey_beach_4.jpg",
            "http://img1.wikia.nocookie.net/__cb20140806200752/disney/images/d/d8/Little-mermaid-1080p-disneyscreencaps.com-782.jpg",
            "http://img3.wikia.nocookie.net/__cb20141022183927/howtotrainyourdragon/images/c/c5/When_gothi_drops_that_flag_we_race.jpg",
            "http://img.gawkerassets.com/img/17jy4w1lonvyijpg/original.jpg"
             };

    objPagerAdapter=new ViewPagerAdapter(ViewPagerActivity.this, _arrayImagePath);
    pager.setAdapter(objPagerAdapter);

    // Calling Volley Library to Download the Image for each URLi

    for(int i=0;i<URL.length;i++)
    {
        DownloadImages(URL[i], i);
    }


}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.view_pager, 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();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}
void DownloadImages(String imageURL_in,final int counter_in)
{
    final String counter=String.valueOf(counter_in);
    ImageRequest imageRequest = new ImageRequest(imageURL_in,
            new Response.Listener<Bitmap>() {

        @Override
        public void onResponse(final Bitmap response) {
            try{
                Log.v("Response Received =",""+counter_in);
                // Saved in SD Card and getting the Path
                String imagePath = SavedInSDCard(response, counter + "_hires"); 
                //Added ImagePath 
                _arrayImagePath.add(imagePath);
                // Notifying the Adapter
                objPagerAdapter.notifyDataSetChanged();


            } catch (Exception e) {e.printStackTrace();}
        }
    }, 0, 0, null, null);
    ApplicationController.getInstance().addToRequestQueue(imageRequest);



}
public String SavedInSDCard(Bitmap bitmap2, String dishId) {

    File dir = new File(ApplicationController.getAppContext()
            .getExternalFilesDir("ViewPager_POC") + "/Cache");
    // Create the storage directory if it does not exist
    if (!dir.exists()) {
        dir.mkdirs();
    }
    String stDishID = dishId;
    String formatedDsihID = stDishID.replace(":", "R");
    File file = new File(dir, formatedDsihID);
    try {
        FileOutputStream out = new FileOutputStream(file);
        bitmap2.compress(Bitmap.CompressFormat.JPEG, 100, out);
        out.flush();
        out.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
    String imgPath = dir + "/" + formatedDsihID;
    return imgPath;
}

这是我的xml文件：

activity_view_pager.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.poc_viewpager.ViewPagerActivity" >

 <android.support.v4.view.ViewPager
    android:id="@+id/pagerView"
    android:layout_width="match_parent"
    android:layout_height="match_parent" /></RelativeLayout>

这是我的ViewPager项目xml文件：

view_pager_item.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<ImageView
    android:id="@+id/images"
    android:layout_width="match_parent"
    android:layout_height="300dp"
    android:layout_alignParentLeft="true"
    android:src="@drawable/ic_launcher" />

<TextView
    android:id="@+id/counter"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_centerHorizontal="true"
    android:layout_marginBottom="44dp"
    android:text="Large Text"
    android:textAppearance="?android:attr/textAppearanceLarge" />

</RelativeLayout>

这是View Pager的适配器类：

ViewPagerAdapter.class

public class ViewPagerAdapter extends PagerAdapter{
Context _context;
LayoutInflater inflater;

ArrayList<String> _arrayImagePath;

public ViewPagerAdapter(Context context_in, ArrayList<String> imagePath_in) {
    _arrayImagePath=imagePath_in;
    _context = context_in;
}

@Override
public int getCount() {
    return _arrayImagePath.size();
}

@Override
public void destroyItem(View container, int position, Object object) {
    // TODO Auto-generated method stub
    ((ViewPager) container).removeView((View) object);
}

@Override
public Object instantiateItem(ViewGroup container, int position) {

    // Declare Variables
    TextView txtCounter;
    ImageView imgView;

    inflater = (LayoutInflater) _context
            .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View itemView = inflater.inflate(R.layout.view_pager_item, container,
            false);

    txtCounter = (TextView) itemView.findViewById(R.id.counter);
    imgView= (ImageView) itemView.findViewById(R.id.images);

    //Setting the values for Image and textview
    txtCounter.setText(""+(position+1));        
    Bitmap bitmap = BitmapFactory.decodeFile(_arrayImagePath.get(position));
    imgView.setImageBitmap(bitmap);


    // Add viewpager_item.xml to ViewPager
    ((ViewPager) container).addView(itemView);

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

}

建议解决这个滞后问题？

Answer 1

在UI线程上使用decodeFile并不是一个好主意，因为它可能需要一段时间。例如，您可以使用AsyncTask。

看一下android开发者方面，有一个非常好的指南： http://developer.android.com/training/displaying-bitmaps/process-bitmap.html

并在您的代码中添加类似的内容：

class BitmapWorkerTask extends AsyncTask<String, Void, Bitmap> {
    private final WeakReference<ImageView> imageViewReference;

    public BitmapWorkerTask(ImageView imageView) {
        imageViewReference = new WeakReference<ImageView>(imageView);
    }
    @Override
    protected Bitmap doInBackground(String... params) {
        String path = params[0];
        return BitmapFactory.decodeFile(path);
    }

    @Override
    protected void onPostExecute(Bitmap bitmap) {
        if (imageViewReference != null && bitmap != null) {
            final ImageView imageView = imageViewReference.get();
            if (imageView != null) {
                imageView.setImageBitmap(bitmap);
        }
    }
}
}

在您的instantiateItem中，您可以使用：

BitmapWorkerTask task = new BitmapWorkerTask(imgView);
task.execute(_arrayImagePath.get(position));

Haven没有对它进行过测试，但它应该有助于理解这个问题。如果您发现错误，请编辑代码。

Android中的ViewPager滞后问题

1 个答案: