Android(安卓)bitmap 一些常用用法

说到Bitmap，Android 的朋友肯定很熟悉了，下面是我对bitmap一些常用方法的总结。之后会陆续更新。

圆角bitmap

    /**     *      * @param source      * @param radius 圆角半径     * @return     */public static Bitmap getRoundCornerBitmap(Bitmap source, float radius) {        if (source == null) return null;        if(radius <= 0){            return source;        }        Bitmap result = Bitmap.createBitmap(source.getWidth(), source.getHeight(), Bitmap.Config.ARGB_8888);        Canvas canvas = new Canvas(result);        Paint paint = new Paint();        paint.setShader(new BitmapShader(source, BitmapShader.TileMode.CLAMP, BitmapShader.TileMode.CLAMP));        paint.setAntiAlias(true);        RectF rectF = new RectF(0f, 0f, source.getWidth(), source.getHeight());        canvas.drawRoundRect(rectF, radius, radius, paint);        return result;    }

读取Asset图片

public static Bitmap getImageFromAssetsFile(String fileName, Context context){        Bitmap image = null;        AssetManager am = context.getResources().getAssets();        InputStream is = null;        try {            is = am.open(fileName);            image = BitmapFactory.decodeStream(is);            is.close();        }catch (IOException e) {            e.printStackTrace();        }finally {            if (is != null){                try {                    is.close();                } catch (IOException e) {                    e.printStackTrace();                }            }        }        return image;    }

缩放图片

 public static Bitmap scaleBitmap(Bitmap bitmap, int dstWidth, int dstHeight) {        if(bitmap == null){            return null;        }        int width = bitmap.getWidth();        int height = bitmap.getHeight();        float scaleWidth = ((float) dstWidth) / width;        float scaleHeight = ((float) dstHeight) / height;        Matrix matrix = new Matrix();        matrix.postScale(scaleWidth, scaleHeight);        Bitmap newbm = Bitmap.createBitmap(bitmap, 0, 0, width, height, matrix, true);        return newbm;    }

读取图片
sampleSize 是指采样率，比如读取原图，sample为1，比如你要读取的图片宽高是原图的1/2，则sampleSize=2,合理使用sampleSize能有效节省内存，比如原图宽高为1080x1920, 而实际只需要显示在108x192的imageview上，最暴力的方法，直接读取原图，但这样很容易oom，或者读取原图，然后放缩到指定尺寸，这个过程也会消耗大量内存，而按照下面的方法，只需要设置sampleSize=10就可以了。

public static Bitmap getBitmapWithPath(String path, int sampleSize){        if(TextUtils.isEmpty(path)){            return null;        }        if(sampleSize <= 0){            sampleSize = 1;        }        File file = new File(path);        if(file.exists() && file.isFile()) {            BitmapFactory.Options boundOptions = new BitmapFactory.Options();            boundOptions.inJustDecodeBounds = false;            boundOptions.inSampleSize = sampleSize;            boundOptions.inDither = true;            boundOptions.inPreferredConfig = Bitmap.Config.ARGB_8888;            return BitmapFactory.decodeFile(path, boundOptions);        }        return null;    }

所以读取一个图片的时候最好的流程这样：读取图片大小（见下述代码）–>计算缩放比例–>读取指定大小的图片（见上述代码）

读取图片大小

 public static Size getBitmapBoundWithPath(String path){        InputStream input = null;        try {            input = new FileInputStream(path);            if(input == null){                return null;            }            BitmapFactory.Options boundOptions = new BitmapFactory.Options();            boundOptions.inJustDecodeBounds = true;            boundOptions.inSampleSize = 1;            BitmapFactory.decodeStream(input, null, boundOptions);//只取宽高，节省内存            input.close();            return new Size(boundOptions.outWidth, boundOptions.outHeight);        } catch (Exception e) {            Log.d(TAG, "exception:" + e.getMessage());            return null;        }finally {            if(input != null){                try {                    input.close();                } catch (IOException e) {                    Log.d(TAG, "exception:" + e.getMessage());                    return null;                }            }        }    }

从视频中获取帧
下面的代码并不能兼容所有的Android机器，比如华为P10用下面方法截帧是不靠谱的。

/**     *      * @param path     * @param time 毫秒     * @return     */ public static Bitmap getFrameFromVideo(String path, long time){        try {            MediaMetadataRetriever retriever = new MediaMetadataRetriever();            retriever.setDataSource(path);            String durationStr = retriever.extractMetadata(MediaMetadataRetriever.METADATA_KEY_DURATION);            long duration = Integer.valueOf(durationStr);            if(time > duration || time < 0){                return null;            }            Bitmap bitmap = retriever.getFrameAtTime(time * 1000);            return bitmap;        }catch (Exception e){            return null;        }    }

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