如何在GridView中动态加载图像或如何优化它的工作？

Question

我的应用程序有一个GridView控件来显示某个目录中的照片。如果目录包含1000或2000张照片，则GridView非常慢，因为一次加载所有照片。

是否可以实现逐渐加载照片，例如，在查看100张照片后，再加载100张照片？或者有更多方法来优化GridView的速度？我很感激你的建议。

我的代码

activity_main.xml中

The piece of code which demonstrate GridView

<GridView
    android:id="@+id/gridview"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:columnWidth="90dp"
    android:numColumns="auto_fit"
    android:verticalSpacing="10dp"
    android:horizontalSpacing="10dp"
    android:stretchMode="columnWidth"
    android:gravity="center"/>

MainActivity.java

public class MainActivity extends Activity {

ImageAdapter myImageAdapter;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    GridView gridview = (GridView) findViewById(R.id.gridview);
    myImageAdapter = new ImageAdapter(this);
    gridview.setAdapter(myImageAdapter);

    String ExternalStorageDirectoryPath = Environment
            .getExternalStorageDirectory()
            .getAbsolutePath();

    String targetPath = ExternalStorageDirectoryPath + "/DCIM/100ANDRO";

    Toast.makeText(getApplicationContext(), targetPath, Toast.LENGTH_LONG).show();
    File targetDirector = new File(targetPath);

    File[] files = targetDirector.listFiles();
    for (File file : files){
        myImageAdapter.add(file.getAbsolutePath());
    }
}

public class ImageAdapter extends BaseAdapter {

    private Context mContext;
    ArrayList<String> itemList = new ArrayList<String>();

    public ImageAdapter(Context c) {
        mContext = c;
    }

    void add(String path){
        itemList.add(path);
    }

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

    @Override
    public Object getItem(int arg0) {
        return null;
    }

    @Override
    public long getItemId(int position) {
        return 0;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ImageView imageView;
        if (convertView == null) {
            imageView = new ImageView(mContext);
            imageView.setLayoutParams(new GridView.LayoutParams(220, 220));
            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
            imageView.setPadding(8, 8, 8, 8);
        } else {
            imageView = (ImageView) convertView;
        }

        Bitmap bm = decodeSampledBitmapFromUri(itemList.get(position), 220, 220);

        imageView.setImageBitmap(bm);
        return imageView;
    }

    public Bitmap decodeSampledBitmapFromUri(String path, int reqWidth, int reqHeight) {

        Bitmap bm = null;

        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeFile(path, options);

        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

        options.inJustDecodeBounds = false;
        bm = BitmapFactory.decodeFile(path, options);

        return bm;
    }

    public int calculateInSampleSize(

            BitmapFactory.Options options, int reqWidth, int reqHeight) {
        final int height = options.outHeight;
        final int width = options.outWidth;
        int inSampleSize = 1;

        if (height > reqHeight || width > reqWidth) {
            if (width > height) {
                inSampleSize = Math.round((float)height / (float)reqHeight);
            } else {
                inSampleSize = Math.round((float)width / (float)reqWidth);
            }
        }

        return inSampleSize;
    }

}

}

Answer 1

你应该使用一个库来加载你的图像，已知的是Glide（https://github.com/bumptech/glide）和Picasso（http://square.github.io/picasso/）。两者都为您处理缓存，并且它们进行延迟加载，因此您的网格应该完美无缺。