Android GalleryView回收

Question

我正在使用带有~40张图像的GalleryView,因为没有回收......所以很慢...

谁能告诉我一个基本的循环利用GalleryView上的getView方法.

public class ImageAdapter extends BaseAdapter {
    int mGalleryItemBackground;
    private Context mContext;

    private Integer[] mImageIds = {
            R.drawable.sample_1,
            R.drawable.sample_2,
            R.drawable.sample_3,
            R.drawable.sample_4,
            R.drawable.sample_5,
            R.drawable.sample_6,
            R.drawable.sample_7
    };

    public ImageAdapter(Context c) {
        mContext = c;

        TypedArray a = c.obtainStyledAttributes(R.styleable.HelloGallery);
        mGalleryItemBackground = a.getResourceId(
                R.styleable.HelloGallery_android_galleryItemBackground, 0);
        a.recycle();
    }

    public int getCount() {
        return mImageIds.length;
    }

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

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

    public View getView(int position, View convertView, ViewGroup parent) {
        ImageView i = new ImageView(mContext);

        i.setImageResource(mImageIds[position]);
        i.setLayoutParams(new Gallery.LayoutParams(150, 100));
        i.setScaleType(ImageView.ScaleType.FIT_XY);
        i.setBackgroundResource(mGalleryItemBackground);

        return i;
    }
}

Answer 1

而不是创建一个新ImageView的getView,你应该转换convertView到你想要的视图.以下是一种方法示例:

public View getView(int position, View cv, ViewGroup parent) {

    if (! convertView istanceof ImageView)
    {
        ImageView cv = new ImageView(mContext);
        cv.setLayoutParams(new Gallery.LayoutParams(150, 100));
        cv.setScaleType(ImageView.ScaleType.FIT_XY);
        cv.setBackgroundResource(mGalleryItemBackground);

    }
    cv.setImageResource(mImageIds[position]);

    return cv;
}

只需转换convertView以匹配您想要的,但首先要确保其正确的视图类型.

更新:您还应该在显示图像之前对图像进行下采样.让我们假设您保存了500x500像素的图像,res/drawable但图像只占用屏幕上的125x125像素.在显示图像之前,您需要对图像进行下采样.要知道您需要对位图进行下采样,您必须首先获得其大小

int maxSize = 125; // make 125 the upper limit on the bitmap size
int resId; // points to bitmap in res/drawable

BitmapFactory.Options opts = new BitmapFactory.Options();
opts.inJustDecodeBounds = true; // Only get the bitmap size, not the bitmap itself
BitmapFactory.decodeResource(c.getResources(), resId, opts);

int w = opts.outHeight, h = opts.outHeight;
int maxDim = (w>h)?w:h; // Get the bigger dimension

现在我们有了大小来计算对图像进行下采样的程度.如果我们有一个500x500的位图,并且我们想要一个125x125的位图,那么我们保留每4个像素中的1个int inSample = 500/125;

int inSample = maxDim/maxSize; 

opts = new BitmapFactory.Options();
opts.inSampleSize = inSample;

现在简单地解码资源,我们有下采样的位图.

Bitmap b = BitmapFactory.decodeResource(c.getResources(), resId, opts);

请记住,原始位图不受影响.您可以再次解码图像并设置opts.inSampleSize为1,您将获得整个500x500位图图像.