Android加載高清大圖

前兩天在面試當中被問到有沒有做過加載高清大圖，當時確實沒有做過，聽面試官提到可以動態(tài)加載圖片的顯示區(qū)域?；貋砗笤诰W上找到了一篇鴻洋大神的博文悔啊-_-!為什么早點沒有看到。廢話不多說代碼如下：

一、BitmapRegionDecoder

BitmapRegionDecoder主要用于顯示圖片的某一塊矩形區(qū)域，所以可以利用它來完成大圖片的動態(tài)區(qū)域顯示。

  • 簡單用法：
    • BitmapRegionDecoder提供了一系列的newInstance方法來構造對象，支持傳入文件路徑，文件描述符，文件的inputstrem等。
      例如：
 BitmapRegionDecoder bitmapRegionDecoder = BitmapRegionDecoder
                                         .newInstance(is, false);
  • BitmapRegionDecoder.decodeRegion()方法，通過傳入矩形區(qū)域即可顯示圖片的指定區(qū)域。
 Bitmap bitmap = bitmapRegionDecoder.decodeRegion(rect, options);

參數一為矩形區(qū)域，參數二為BitmapFactory.Options。

  • 一個簡單的使用例子：
 // load Assets image
        try {
            InputStream is = getAssets().open("qm.jpg");
            BitmapFactory.Options tmpOptions = new BitmapFactory.Options();
            tmpOptions.inJustDecodeBounds = true;
            BitmapFactory.decodeStream(is, null, tmpOptions);
            int width = tmpOptions.outWidth;
            int height = tmpOptions.outHeight;

            // 設置顯示圖片的中心區(qū)域
            BitmapRegionDecoder bitmapRegionDecoder = BitmapRegionDecoder
                                             .newInstance(is, false);
            BitmapFactory.Options options = new BitmapFactory.Options();
            options.inJustDecodeBounds = true;
            // JPG圖片沒有Aphla通道使用該顏色模式更加節(jié)省內存
            options.inPreferredConfig = Bitmap.Config.RGB_565;
            // 設置顯示區(qū)域的矩形大小
            Rect rect = new Rect(
                    width / 2 - 100, height / 2 - 100,
                    width / 2 + 100, height / 2 + 100);
            // 通過BitmapRegionDecoder來解析顯示區(qū)域的圖像
            Bitmap bitmap = bitmapRegionDecoder.decodeRegion(rect, options);
            mShow.setImageBitmap(bitmap);
        } catch (IOException e) {
            e.printStackTrace();
        }

一個簡單的使用例子，整體自定義View的設計思想，即是通過滑動時獲得的坐標不斷設置矩形區(qū)域的偏移坐標，然后不斷繪制View來完成動態(tài)顯示大圖的效果。具體代碼大家可以自行參考鴻洋大神的博客，我這里將我注釋的代碼分享給大家。

二、LargeImageView

  • 首先手勢檢測的兩個類：BaseGestureDetector、MoveGestureDetector。
public abstract class BaseGestureDetector {

    protected boolean mGestureInProgress;

    protected MotionEvent mPreMotionEvent;
    protected MotionEvent mCurrentMotionEvent;

    protected Context mContext;

    public BaseGestureDetector(Context context) {
        mContext = context;
    }

    public boolean onTouchEvent(MotionEvent event) {

        if (!mGestureInProgress)
        {
            handleStartProgressEvent(event);
        } else
        {
            handleInProgressEvent(event);
        }

        return true;

    }

    protected abstract void handleInProgressEvent(MotionEvent event);

    protected abstract void handleStartProgressEvent(MotionEvent event);

    protected abstract void updateStateByEvent(MotionEvent event);

    protected void resetState()
    {
        if (mPreMotionEvent != null)
        {
            mPreMotionEvent.recycle();
            mPreMotionEvent = null;
        }
        if (mCurrentMotionEvent != null)
        {
            mCurrentMotionEvent.recycle();
            mCurrentMotionEvent = null;
        }
        mGestureInProgress = false;
    }
}

這里有一個關于抽象類的構造方法需要提一下，具體說明大家可以自行移至這里,結論即是抽象類的子類在創(chuàng)建對象時，也會跟非抽象類的子類一樣，都會默認調用父類的無參構造方法。

public class MoveGestureDetector extends BaseGestureDetector {

    private PointF mCurrentPointer;
    private PointF mPrePointer;
    //僅僅為了減少創(chuàng)建內存
    private PointF mDeltaPointer = new PointF();

    //用于記錄最終結果，并返回
    private PointF mExtenalPointer = new PointF();

    private OnMoveGestureListener mListenter;


    public MoveGestureDetector(Context context, OnMoveGestureListener listener)
    {
        super(context);
        mListenter = listener;
    }

    @Override
    protected void handleInProgressEvent(MotionEvent event)
    {
        int actionCode = event.getAction() & MotionEvent.ACTION_MASK;
        switch (actionCode)
        {
            case MotionEvent.ACTION_CANCEL:
            case MotionEvent.ACTION_UP:
                mListenter.onMoveEnd(this);
                resetState();
                break;
            case MotionEvent.ACTION_MOVE:
                updateStateByEvent(event);
                boolean update = mListenter.onMove(this);
                if (update)
                {
                    mPreMotionEvent.recycle();
                    mPreMotionEvent = MotionEvent.obtain(event);
                }
                break;

        }
    }

    @Override
    protected void handleStartProgressEvent(MotionEvent event)
    {
        int actionCode = event.getAction() & MotionEvent.ACTION_MASK;
        switch (actionCode)
        {
            case MotionEvent.ACTION_DOWN:
                resetState();//防止沒有接收到CANCEL or UP ,保險起見
                mPreMotionEvent = MotionEvent.obtain(event);
                updateStateByEvent(event);
                break;
            case MotionEvent.ACTION_MOVE:
                mGestureInProgress = mListenter.onMoveBegin(this);
                break;
        }

    }

    protected void updateStateByEvent(MotionEvent event)
    {
        final MotionEvent prev = mPreMotionEvent;

        mPrePointer = caculateFocalPointer(prev);
        mCurrentPointer = caculateFocalPointer(event);

//        Log.e("TAG", mPrePointer.toString() + " ,  " + mCurrentPointer);

        boolean mSkipThisMoveEvent = prev.getPointerCount() != event.getPointerCount();

//        Log.e("TAG", "mSkipThisMoveEvent = " + mSkipThisMoveEvent);
        mExtenalPointer.x = mSkipThisMoveEvent ? 0 : mCurrentPointer.x - mPrePointer.x;
        mExtenalPointer.y = mSkipThisMoveEvent ? 0 : mCurrentPointer.y - mPrePointer.y;

    }

    /**
     * 根據event計算多指中心點
     *
     * @param event
     * @return
     */
    private PointF caculateFocalPointer(MotionEvent event)
    {
        final int count = event.getPointerCount();
        float x = 0, y = 0;
        for (int i = 0; i < count; i++)
        {
            x += event.getX(i);
            y += event.getY(i);
        }

        x /= count;
        y /= count;

        return new PointF(x, y);
    }


    public float getMoveX()
    {
        return mExtenalPointer.x;

    }

    public float getMoveY()
    {
        return mExtenalPointer.y;
    }


    public interface OnMoveGestureListener
    {
        public boolean onMoveBegin(MoveGestureDetector detector);

        public boolean onMove(MoveGestureDetector detector);

        public void onMoveEnd(MoveGestureDetector detector);
    }

    public static class SimpleMoveGestureDetector implements OnMoveGestureListener
    {

        @Override
        public boolean onMoveBegin(MoveGestureDetector detector)
        {
            return true;
        }

        @Override
        public boolean onMove(MoveGestureDetector detector)
        {
            return false;
        }

        @Override
        public void onMoveEnd(MoveGestureDetector detector)
        {
        }
    }

}

關于這兩個檢測手勢移動的類我還沒有研究，各位同學可以自行研究。

  • 最后自定義View的代碼如下：
public class LargeImageView extends View {
    private BitmapRegionDecoder mDecoder;
    /**
     * 圖片的寬高
     */
    private int mImageWidth,mImageHeight;
    /**
     * 矩形顯示的區(qū)域（volatile修飾的對象線程安全）
     */
    private volatile Rect mRect = new Rect();
    /**
     * 手勢檢測
     */
    private MoveGestureDetector mDetector;

    private static final BitmapFactory.Options options = 
                              new BitmapFactory.Options();

    static {
        options.inPreferredConfig = Bitmap.Config.RGB_565;
    }

    public LargeImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public void setInputStream(InputStream is) {
        try {
            mDecoder = BitmapRegionDecoder.newInstance(is, false);
            BitmapFactory.Options tmpOptions = new BitmapFactory.Options();
            tmpOptions.inJustDecodeBounds = true;
            BitmapFactory.decodeStream(is, null, tmpOptions);
            mImageWidth = tmpOptions.outWidth;
            mImageHeight = tmpOptions.outHeight;
//            Log.d("xns", "width:" + mImageWidth + " ,height:" + mImageHeight);
            // 重新布局View
            requestLayout();
            invalidate();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (is != null) {
                    is.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    public void init() {
        mDetector = new MoveGestureDetector(getContext(), 
          new MoveGestureDetector.SimpleMoveGestureDetector() {

            @Override
            public boolean onMove(MoveGestureDetector detector) {
                int moveX = (int) detector.getMoveX();
                int moveY = (int) detector.getMoveY();
                // 只要圖片在X或Y方向上大于View的寬高才進行矩形區(qū)域的偏移
                if (mImageWidth > getWidth()) {
                    mRect.offset(-moveX, 0);
                    checkWidth();
                    // 偏移后重新繪制顯示圖片
                    invalidate();
                }
                if (mImageHeight > getHeight())
                {
                    mRect.offset(0, -moveY);
                    checkHeight();
                    invalidate();
                }
                return true;
            }

        });
    }

    private void checkHeight() {
        Rect rect = mRect;
        int imageHeight = mImageHeight;

        if (rect.bottom > imageHeight)
        {
            rect.bottom = imageHeight;
            rect.top = imageHeight - getHeight();
        }

        if (rect.top < 0)
        {
            rect.top = 0;
            rect.bottom = getHeight();
        }
    }

    private void checkWidth() {
        Rect rect = mRect;
        int imageWidth = mImageWidth;

        if (rect.right > imageWidth) {
            rect.right = imageWidth;
            rect.left = imageWidth - getWidth();
        }

        if (rect.left < 0) {
            rect.left = 0;
            rect.right = getWidth();
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        //Log.d("xns", "x:" + event.getX() + " ,y:" + event.getY());
        mDetector.onTouchEvent(event);
        return true;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        int width = getMeasuredWidth();
        int height = getMeasuredHeight();

        int imageWidth = mImageWidth;
        int imageHeight = mImageHeight;

        // 默認顯示圖片中心區(qū)域
        mRect.left = imageWidth / 2 - width / 2;
        mRect.top = imageHeight / 2 - height / 2;
        mRect.right = mRect.left + width;
        mRect.bottom = mRect.top + height;

    }

    @Override
    protected void onDraw(Canvas canvas) {

        Bitmap bitmap = mDecoder.decodeRegion(mRect, options);
        canvas.drawBitmap(bitmap, 0, 0, null);
    }
}
  • 使用代碼如下：
public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";
    private LargeImageView mLIv;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mLIv = (LargeImageView) findViewById(R.id.iv_large);

        // load Assets image
        try {
            InputStream is = getAssets().open("qm.jpg");
            // 調用自定義大圖加載View
            mLIv.setInputStream(is);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

寫在最后

最近找工作找的很煩躁，最后寫給自己的寄語，以此激勵自己一下，靜心思考，勇往直前。

最后編輯于 ：
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