使用Viewpager制作图片阅读器（2）-优化

来源：互联网发布：淘宝事件编辑：程序博客网时间：2024/06/05 03:31

在原来的基础上再优化一下，当加载完48张图（大部分720P以上的）片以后，我的机器是使用的31.923M的内存，

在这里请先看博客：http://blog.csdn.net/guolin_blog/article/details/9316683

那个博客上面的方法是很实用的，可以节省很多内存，因此在原来的基础上修改setImageVIew的方法：

修改

Activity的

@Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        mImageLoader = new ImageLoader();        initViews();    }

</pre><pre class="java" name="code"> mViewPager.setAdapter(new ViewPagerAdapter(MainActivity.this, mImageLoader));

ViewPagerAdapter的

public ViewPagerAdapter(Context context, ImageLoader imageLoader){
        mContext = context;
        mImageLoader = imageLoader;
    }

@Override    public Object instantiateItem(ViewGroup container, int position) {        int index = position % DataConfig.ALL_IMAGE_IDS.length;        int id = DataConfig.ALL_IMAGE_IDS[index];               View view = null;        view = LayoutInflater.from(mContext).inflate(R.layout.details, null);        ImageView imageView = (ImageView)view.findViewById(R.id.image);       // imageView.setImageResource(id);        Bitmap bitmap = mImageLoader.decodeSampledBitmapFromResource(mContext.getResources(), id,                400, 300);        imageView.setImageBitmap(bitmap);        container.addView(view);        return view;    }

ImageLoader的源码：

public class ImageLoader {        public static ImageLoader mImageLoader = null;    private static LruCache<String , Bitmap> mMemCache;    public ImageLoader(){        int maxMemory = (int)Runtime.getRuntime().maxMemory();        int cacheSize = maxMemory / 8;        mMemCache = new LruCache<String, Bitmap>(cacheSize){            @Override            protected int sizeOf(String key, Bitmap value) {                return value.getByteCount();            }        };    }        public static ImageLoader getInstance(){        if (null == mImageLoader){            mImageLoader = new ImageLoader();        }                return mImageLoader;    }        public Bitmap getBitmapFromMemoryCache(String key){        return mMemCache.get(key);    }        public void addBitmapFromMemoryCache(String key , Bitmap bitmap){        if (null == getBitmapFromMemoryCache(key)){            mMemCache.put(key, bitmap);        }    }        public  Bitmap decodeSampledBitmapFromResource(Resources res, int resId,            int reqWidth, int reqHeight) {        // 第一次解析将inJustDecodeBounds设置为true，来获取图片大小        final BitmapFactory.Options options = new BitmapFactory.Options();        options.inJustDecodeBounds = true;        BitmapFactory.decodeResource(res, resId, options);        // 调用上面定义的方法计算inSampleSize值        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);        // 使用获取到的inSampleSize值再次解析图片        options.inJustDecodeBounds = false;        return BitmapFactory.decodeResource(res, resId, options);    }        /** 完成没有意义  options.inSampleSize = 1;  跟直接使用setImageBitmap 使用内存大少一样 */    public  Bitmap decodeSampledBitmapFromResource(Resources res, int resId            ) {        // 第一次解析将inJustDecodeBounds设置为true，来获取图片大小        final BitmapFactory.Options options = new BitmapFactory.Options();        options.inJustDecodeBounds = true;        BitmapFactory.decodeResource(res, resId, options);        // 调用上面定义的方法计算inSampleSize值        options.inSampleSize = 1;        // 使用获取到的inSampleSize值再次解析图片        options.inJustDecodeBounds = false;        return BitmapFactory.decodeResource(res, resId, options);    }    public static int calculateInSampleSize(BitmapFactory.Options options,            int reqWidth, int reqHeight) {        // 源图片的高度和宽度        final int height = options.outHeight;        final int width = options.outWidth;        int inSampleSize = 1;        if (height > reqHeight || width > reqWidth) {            // 计算出实际宽高和目标宽高的比率            final int heightRatio = Math.round((float) height / (float) reqHeight);            final int widthRatio = Math.round((float) width / (float) reqWidth);            // 选择宽和高中最小的比率作为inSampleSize的值，这样可以保证最终图片的宽和高            // 一定都会大于等于目标的宽和高。            inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;        }        return inSampleSize;    }        public static Bitmap decodeSampledBitmapFromResource(String pathName,            int reqWidth, int reqHeight) {        // 第一次解析将inJustDecodeBounds设置为true，来获取图片大小        final BitmapFactory.Options options = new BitmapFactory.Options();        options.inJustDecodeBounds = true;        BitmapFactory.decodeFile(pathName, options);        // 调用上面定义的方法计算inSampleSize值        options.inSampleSize = calculateInSampleSize(options, reqWidth , reqHeight);        // 使用获取到的inSampleSize值再次解析图片        options.inJustDecodeBounds = false;        return BitmapFactory.decodeFile(pathName, options);    }}

就只有现在我机器的使用内存为 11.141M，当然是我设置的太少了 Bitmap bitmap = mImageLoader.decodeSampledBitmapFromResource(mContext.getResources(), id,
400, 300); 这个因人而异，需求而定，我这里只是引导大家使用这个方法！

接下来给我们的图片翻页时加一点效果，就要使用到ViewPager.PageTransformer这个类：

加上代码// mViewPager.setPageTransformer(true, new ZoomOutPageTransformer()) ;
mViewPager.setPageTransformer(true, new DepthPageTransformer()) ;

DepthPageTransformer 跟 ZoomOuDepthPageTransformer 是官方提供的滑动效果：

先看DepthPageTransformer 效果如下：

ZoomOutPageTransformer 的效果如下:

代码

public class DepthPageTransformer implements PageTransformer {    private static float MIN_SCALE = 0.75f;     @Override    public void transformPage(View view, float position) {        int pageWidth = view.getWidth();        Log.d("dd", "position:"+position);        if (position < -1) { // [-Infinity,-1)                                // This page is way off-screen to the left.            view.setAlpha(0);        } else if (position <= 0) { // [-1,0]                                    // Use the default slide transition when                                    // moving to the left page            view.setAlpha(1);            view.setTranslationX(0);            view.setScaleX(1);            view.setScaleY(1);        } else if (position <= 1) { // (0,1]                                    // Fade the page out.            view.setAlpha(1 - position);            // Counteract the default slide transition            view.setTranslationX(pageWidth * -position);            // Scale the page down (between MIN_SCALE and 1)            float scaleFactor = MIN_SCALE + (1 - MIN_SCALE)                    * (1 - Math.abs(position));            view.setScaleX(scaleFactor);            view.setScaleY(scaleFactor);        } else { // (1,+Infinity]                    // This page is way off-screen to the right.            view.setAlpha(0);         }    } }

public class ZoomOutPageTransformer implements ViewPager.PageTransformer {         private static final float MIN_SCALE = 0.85f;         private static final float MIN_ALPHA = 0.2f;         public void transformPage(View view, float position)     {                int pageWidth = view.getWidth();                int pageHeight = view.getHeight();           Log.d("dd",view.getTag()+" position:"+position);        if (position < -1) { // [-Infinity,-1)             // This page is way off-screen to the left.                         view.setAlpha(0);                 } else if (position <= 1) { // [-1,1]             // Modify the default slide transition to shrink the page as well                         float scaleFactor = Math.max(MIN_SCALE, 1 - Math.abs(position));                        float vertMargin = pageHeight * (1 - scaleFactor) / 2;                         float horzMargin = pageWidth * (1 - scaleFactor) / 2;                        if (position < 0) {                                view.setTranslationX(horzMargin - vertMargin / 2);                       }             else {                                view.setTranslationX(-horzMargin + vertMargin / 2);                        }              // Scale the page down (between MIN_SCALE and 1)                         view.setScaleX(scaleFactor);                        view.setScaleY(scaleFactor);              // Fade the page relative to its size.                         view.setAlpha(MIN_ALPHA +(scaleFactor - MIN_SCALE) / (1 - MIN_SCALE) * (1 - MIN_ALPHA));               } else { // (1,+Infinity]             // This page is way off-screen to the right.                        view.setAlpha(0);                }     }}

在public void transformPage(View view, float position) 这个方法中

view  是当前view   或者是下一个view，那个position是float的类型，解析一下，可以加打印可以看到

position 是在滑动过程是是变化的增加log调试  在view都加上tag ，

Override    public Object instantiateItem(ViewGroup container, int position) {        int index = position % DataConfig.ALL_IMAGE_IDS.length;        int id = DataConfig.ALL_IMAGE_IDS[index];               View view = null;        view = LayoutInflater.from(mContext).inflate(R.layout.details, null);

// 加上TAG        view.setTag(index);        ImageView imageView = (ImageView)view.findViewById(R.id.image);       // imageView.setImageResource(id);        Bitmap bitmap = mImageLoader.decodeSampledBitmapFromResource(mContext.getResources(), id,                400, 300);        imageView.setImageBitmap(bitmap);        container.addView(view);

        return view;    }

看log

仔细观察从滑动到最后停止

view 当前页跟下一页交替打印的

可以理解为最左上角为 0.0放位置，所有的view的宽度都是为1的

那么往左边滑动时当前页position就是当前页左上角相对于 0.0的位移，下一个的position，下一页的左定点相对对0.0放位移

所有滑动到一半时前一页就是-0.5 ，下一页就是0.5

滑动结束时就是 -1.0 跟0

下载地址：http://download.csdn.net/detail/hewence1/7848639

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