android canvas 绘制bitmap并保存到本地

自定义一个view，重载draw方法（不是重载ondraw，不然图片保存下来是空白的。）在activity里面findviewbyid找到view，用view调用draw方法。

在activity的oncreate里面：

if (mBackgroundBitmap == null) {            mBackgroundBitmap = Bitmap.createBitmap(screenWidth, screenHeight, Bitmap.Config.RGB_565);            canvas = new Canvas(mBackgroundBitmap);        }        myView.draw(canvas);

自定义的myView（extend View）里面，

@Override    public void draw(Canvas canvas) {//canvas.drawLine().....}

保存到本地：

activity里面一些方法，

public Bitmap getBitmap() {                Bitmap whiteBgBitmap = Bitmap.createBitmap(mBackgroundBitmap.getWidth(), mBackgroundBitmap.getHeight(),                Bitmap.Config.ARGB_8888);        Canvas canvas = new Canvas(whiteBgBitmap);        canvas.drawColor(Color.WHITE);        canvas.drawBitmap(mBackgroundBitmap, 0, 0, null);        return whiteBgBitmap;    }

public boolean addGraphToGallery(Bitmap bmp) {        boolean result = false;        try {            File photo = new File(getAlbumStorageDir("cece"), String.format("cece_bitmap_%d.jpg",                    System.currentTimeMillis()));            saveBitmapToJPG(bmp, photo);            Intent mediaScanIntent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);            Uri contentUri = Uri.fromFile(photo);            mediaScanIntent.setData(contentUri);            SpiderNetActivity.this.sendBroadcast(mediaScanIntent);            result = true;        } catch (IOException e) {            e.printStackTrace();        }        return result;    }

public void saveBitmapToJPG(Bitmap bitmap, File photo) throws IOException {        Bitmap newBitmap = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), Bitmap.Config.ARGB_8888);        Canvas canvas = new Canvas(newBitmap);        canvas.drawColor(Color.WHITE);        canvas.drawBitmap(bitmap, 0, 0, null);        OutputStream stream = new FileOutputStream(photo);        newBitmap.compress(Bitmap.CompressFormat.JPEG, 80, stream);        stream.close();    }

public File getAlbumStorageDir(String albumName) {        // Get the directory for the user's public pictures directory.        File file = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES), albumName);        if (!file.mkdirs()) {            Log.e("SignaturePad", "Directory not created");        }        return file;    }

开始保存：

Bitmap spiderNetBitmap = getBitmap();if (addGraphToGallery(spiderNetBitmap)) {                    Toast.makeText(SpiderNetActivity.this, "Spider graph saved into the Gallery", Toast.LENGTH_SHORT)                            .show();                } else {                    Toast.makeText(SpiderNetActivity.this, "Unable to store Spider graph", Toast.LENGTH_SHORT).show();                }

不要忘记在manifest里面添加存储权限：

bitmap转byte[] 方法：

public byte[] Bitmap2Bytes(Bitmap bm) {        ByteArrayOutputStream baos = new ByteArrayOutputStream();        bm.compress(Bitmap.CompressFormat.PNG, 100, baos);        return baos.toByteArray();    }

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