2.Bitmap优化

主要有两类方法：
一、decodeBitmap:对Bitmap不压缩，但是会根据屏幕的密度合适的进行缩放压缩
二、compressBimtap:对Bitmap进行超过最大宽高的压缩，同时也会根据屏幕的密度合适的进行缩放压缩。





publicclass BitmapDecodeUtil {

    privatestatic final int DEFAULT_DENSITY = 240;

    privatestatic final float SCALE_FACTOR = 0.75f;

    privatestatic final Bitmap.Config DEFAULT_BITMAP_CONFIG = Bitmap.Config.RGB_565;

    privatestatic BitmapFactory.Options getBitmapOptions(Context context) {

        BitmapFactory.Options options = newBitmapFactory.Options();

        options.inScaled = true;

        options.inPreferredConfig = DEFAULT_BITMAP_CONFIG;

        options.inPurgeable = true;

        options.inInputShareable = true;

        options.inJustDecodeBounds = false;

        if(Build.VERSION.SDK_INT <= Build.VERSION_CODES.GINGERBREAD_MR1) {

            Field field = null;

            try{

                field = BitmapFactory.Options.class.getDeclaredField("inNativeAlloc");

                field.setAccessible(true);

                field.setBoolean(options, true);

            } catch(NoSuchFieldException e) {

                e.printStackTrace();

            } catch(IllegalAccessException e) {

                e.printStackTrace();

            }

        }

        intdisplayDensityDpi = context.getResources().getDisplayMetrics().densityDpi;

        floatdisplayDensity = context.getResources().getDisplayMetrics().density;

        if(displayDensityDpi > DEFAULT_DENSITY && displayDensity > 1.5f) {

            intdensity = (int) (displayDensityDpi * SCALE_FACTOR);

            options.inDensity = density;

            options.inTargetDensity = density;

        }

        returnoptions;

    }

    publicstatic Bitmap decodeBitmap(Context context, intresId) {

        checkParam(context);

        returnBitmapFactory.decodeResource(context.getResources(), resId, getBitmapOptions(context));

    }

    publicstatic Bitmap decodeBitmap(Context context, String pathName) {

        checkParam(context);

        returnBitmapFactory.decodeFile(pathName, getBitmapOptions(context));

    }

    publicstatic Bitmap decodeBitmap(Context context, InputStream is) {

        checkParam(context);

        checkParam(is);

        returnBitmapFactory.decodeStream(is, null, getBitmapOptions(context));

    }

    publicstatic Bitmap compressBitmap(Context context,intresId, intmaxWidth, intmaxHeight) {

        checkParam(context);

        finalTypedValue value = newTypedValue();

        InputStream is = null;

        try{

            is = context.getResources().openRawResource(resId, value);

            returncompressBitmap(context, is, maxWidth, maxHeight);

        } catch(Exception e) {

            e.printStackTrace();

        } finally{

            if(is != null) {

                try{

                    is.close();

                } catch(IOException e) {

                    e.printStackTrace();

                }

            }

        }

        returnnull;

    }

    publicstatic Bitmap compressBitmap(Context context, String pathName, intmaxWidth, intmaxHeight) {

        checkParam(context);

        InputStream is = null;

        try{

            is = newFileInputStream(pathName);

            returncompressBitmap(context, is, maxWidth, maxHeight);

        } catch(FileNotFoundException e) {

            e.printStackTrace();

        } finally{

            if(is != null) {

                try{

                    is.close();

                } catch(IOException e) {

                    e.printStackTrace();

                }

            }

        }

        returnnull;

    }

    publicstatic Bitmap compressBitmap(Context context, InputStream is, intmaxWidth, intmaxHeight) {

        checkParam(context);

        checkParam(is);

        BitmapFactory.Options opt = newBitmapFactory.Options();

        opt.inJustDecodeBounds = true;

        BitmapFactory.decodeStream(is, null, opt);

        intheight = opt.outHeight;

        intwidth = opt.outWidth;

        intsampleSize = computeSampleSize(width, height, maxWidth, maxHeight);

        BitmapFactory.Options options = getBitmapOptions(context);

        options.inSampleSize = sampleSize;

        returnBitmapFactory.decodeStream(is, null, options);

    }

    privatestatic int computeSampleSize(intwidth, intheight, intmaxWidth, intmaxHeight) {

        intinSampleSize = 1;

        if(height > maxHeight || width > maxWidth) {

            finalint heightRate = Math.round((float) height / (float) maxHeight);

            finalint widthRate = Math.round((float) width / (float) maxWidth);

            inSampleSize = heightRate < widthRate ? heightRate : widthRate;

        }

        if(inSampleSize % 2!= 0) {

            inSampleSize -= 1;

        }

        returninSampleSize <= 1? 1: inSampleSize;

    }

    privatestatic <T> voidcheckParam(T param){

        if(param == null)

            thrownew NullPointerException();

    }

}