其实android拍照这个地方还是有很多注意事项的，我在上个项目中就遇到一些坑，因此我想把它记录下来，希望能帮助一些跟我遇到的同样的问题的人

如果你在项目中遇到以下问题：

通过系统路径，拍出来的图片不清楚
在某些情况下，onActivityResult(int requestCode, int resultCode, Intent data) 回调方法中，data为null
有些时候，在某些手机拍照之后会闪退，报空指针错误，等等
有些时候在拍完照片之后，点击确认按钮之后，无法返回到前一个Activity

可以继续往下看，否则的话，就跳过吧，不能耽误你的时间

先说第一种情况，如果直接调用系统相机，一般系统会把图片放在默认的路径，然后通过回调函数onActivityResult(int requestCode, int resultCode, Intent data)中的data拿值，Bitmap bitmap =(Bitmap) data.getExtras().get("data"),这样就拿到bitmap了。值得注意的是，返回的这个图片是缩略图并不是原图。如果是需要拍身份证照片，录入信息的，不能用考虑这种。当然这种调用相机也会有人用到，先贴一下代码：

 public class MainActivity extends AppCompatActivity {

     public static final int TAKE_PHOTO = 111;

     private Button mButton;
     private ImageView mImageView;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         mButton = (Button) findViewById(R.id.takePhoto);
         mImageView = (ImageView) findViewById(R.id.img);

         mButton.setOnClickListener(new View.OnClickListener() {
             @Override
             public void onClick(View view) {
                 takePhoto();
             }
         });
     }

     public void takePhoto() {
         Intent captureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
         startActivityForResult(captureIntent, TAKE_PHOTO);
     }

     @Override
     protected void onActivityResult(int requestCode, int resultCode, Intent data) {
         super.onActivityResult(requestCode, resultCode, data);

         if (resultCode == RESULT_OK) {

             if (requestCode == TAKE_PHOTO) {
                 Bitmap bitmap = (Bitmap) data.getExtras().get("data");
                 //拿到bitmap，做喜欢做的事情把  ---> 显示 or上传？

                 mImageView.setImageBitmap(bitmap);

                 //upload
             }
         }


     }

 }

第二种情况，onActivityResult(int requestCode, int resultCode, Intent data) 回调方法中，data为null。这种情况，如果代码没错误，那么产生这种原因是什么呢？其实当你自定义拍照路径之后，回调函数中，返回的data就为null了，那么你拿图片资源就只能通过file转化成bitmap的了。下面我会把Bitmap工具类提供出来

public class MainActivity extends AppCompatActivity {

    public static final int TAKE_PHOTO = 111;

    private Button mButton;
    private ImageView mImageView;


    //保存 照片的目录
    private String path = Environment.getExternalStorageDirectory().getAbsolutePath() + File.separator + "mms";
    private File photo_file = new File(path);
    private String photoPath ;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mButton = (Button) findViewById(R.id.takePhoto);
        mImageView = (ImageView) findViewById(R.id.img);

        mButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                takePhoto();
            }
        });
    }

    public void takePhoto() {
        Intent captureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);

        if (!photo_file.exists()) {
            photo_file.mkdirs();
        }
        photo_file = new File(path, "/temp.jpg");
        photoPath = path + "/temp.jpg";
        if (photo_file != null) {
            captureIntent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(photo_file));
            startActivityForResult(captureIntent, TAKE_PHOTO);
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {

        super.onActivityResult(requestCode, resultCode, data);
        if (resultCode == RESULT_OK) {

            if (requestCode == TAKE_PHOTO) {
                //这种情况下 data是为null的，因为自定义了路径

            }
        }


    }

}

这种情况下，因为data为null，所以正确做法应该是从 photoPath中来获取bitmap。在后面会写出全部代码的，这里只是说明为啥data会为null

在某些手机拍照之后会闪退，报空指针错误。这个错误主要是因为当点击拍照时，某些情况下，系统会认为这个是耗费资源的操作，所以会未经你允许的情况下把之前的Activity给销毁了，所以当再次回到上个界面中，生命周期会重新来一遍，所以当执行到onActivityResult(int requestCode, int resultCode, Intent data)中，photoPath还是为空，所以报了空指针异常。解决办法如下：

   @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putString("photoPath", photoPath);
        Log.d(TAG, "onSaveInstanceState");
    }
    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
        if (TextUtils.isEmpty(photoPath)) {
            photoPath = savedInstanceState.getString("photoPath");
        }
        Log.d(TAG, "onRestoreInstanceState");
    }

通过onSaveInstanceState(Bundle outState)把数据保存起来，然后界面确实被系统销毁了，那么就会执行onRestoreInstanceState(Bundle savedInstanceState)方法，在这个方法中就可以取到数据了，从而恢复界面。

有些时候在拍完照片之后，点击确认按钮之后，无法返回到前一个Activity,这个问题主要是文件建的不对，导入图片资源无法写进去，点击确定后也无法回退到上个界面。这里就按照我这种创建的方式把。

完整拍照上传图片的代码如下：

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "MainActivity";

    public static final int TAKE_PHOTO = 111;

    private Button mButton;
    private ImageView mImageView;

    //保存 照片的目录
    private String path = Environment.getExternalStorageDirectory().getAbsolutePath() + File.separator + "mms";
    private File photo_file = new File(path);
    private String photoPath;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mButton = (Button) findViewById(R.id.takePhoto);
        mImageView = (ImageView) findViewById(R.id.img);

        mButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                takePhoto();
            }
        });
    }

    public void takePhoto() {
        Intent captureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);

        if (!photo_file.exists()) {
            photo_file.mkdirs();
        }
        photo_file = new File(path, "/temp.jpg");
        photoPath = path + "/temp.jpg";
        if (photo_file != null) {
            captureIntent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(photo_file));
            startActivityForResult(captureIntent, TAKE_PHOTO);
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {

        super.onActivityResult(requestCode, resultCode, data);
        if (resultCode == RESULT_OK) {

            if (requestCode == TAKE_PHOTO) {
                //这中情况下 data是为null的，因为自定义了路径 所以通过这个路径来获取
                Bitmap smallBitmap = BitmapUtil.getSmallBitmap(photoPath);

                // ok 拿到图片的base64 上传
                String base64 = BitmapToBase64Util.bitmapToBase64(smallBitmap);
            }
        }

    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putString("photoPath", photoPath);
        Log.d(TAG, "onSaveInstanceState");
    }

    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
        if (TextUtils.isEmpty(photoPath)) {
            photoPath = savedInstanceState.getString("photoPath");
        }
        Log.d(TAG, "onRestoreInstanceState");
    }

}

`BitmapUtil`

@SuppressLint("NewApi")
public class BitmapUtil {
    // 计算图片的缩放值
    public static int calculateInSampleSize(BitmapFactory.Options options,
            int reqWidth, int reqHeight) {
        final int height = options.outHeight;
        final int width = options.outWidth;
        int inSampleSize = 1;

        if (height > reqHeight || width > reqWidth) {
            final int heightRatio = Math.round((float) height
                    / (float) reqHeight);
            final int widthRatio = Math.round((float) width / (float) reqWidth);
            inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;
        }
        return inSampleSize;
    }

    // 根据路径获得图片并压缩，返回bitmap用于显示
    public static Bitmap getSmallBitmap(String filePath) {
        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeFile(filePath, options);
        // Calculate inSampleSize
        options.inSampleSize = calculateInSampleSize(options, 200, 380);

        // Decode bitmap with inSampleSize set
        options.inJustDecodeBounds = false;

        return BitmapFactory.decodeFile(filePath, options);
    }

    // 根据路径获得图片并压缩，返回bitmap用于显示
    public static Bitmap getSmallBitmap(InputStream is) {
        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeStream(is, null, options);
        // Calculate inSampleSize
        options.inSampleSize = calculateInSampleSize(options, 480, 800);

        // Decode bitmap with inSampleSize set
        options.inJustDecodeBounds = false;

        return BitmapFactory.decodeStream(is, null, options);
    }

    public static Bitmap comp(Bitmap image) {

        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        image.compress(Bitmap.CompressFormat.JPEG, 100, baos);
        if (baos.toByteArray().length / 1024 > 1024) {// 判断如果图片大于1M,进行压缩避免在生成图片（BitmapFactory.decodeStream）时溢出
            baos.reset();// 重置baos即清空baos
            image.compress(Bitmap.CompressFormat.JPEG, 40, baos);// 这里压缩50%，把压缩后的数据存放到baos中
        }
        ByteArrayInputStream isBm = new ByteArrayInputStream(baos.toByteArray());
        BitmapFactory.Options newOpts = new BitmapFactory.Options();
        // 开始读入图片，此时把options.inJustDecodeBounds 设回true了
        newOpts.inJustDecodeBounds = true;
        Bitmap bitmap = BitmapFactory.decodeStream(isBm, null, newOpts);
        newOpts.inJustDecodeBounds = false;
        int w = newOpts.outWidth;
        int h = newOpts.outHeight;
        // 现在主流手机比较多是800*480分辨率，所以高和宽我们设置为
        float hh = 800f;// 这里设置高度为800f
        float ww = 480f;// 这里设置宽度为480f
        // 缩放比。由于是固定比例缩放，只用高或者宽其中一个数据进行计算即可
        int be = 1;// be=1表示不缩放
        if (w > h && w > ww) {// 如果宽度大的话根据宽度固定大小缩放
            be = (int) (newOpts.outWidth / ww);
        } else if (w < h && h > hh) {// 如果高度高的话根据宽度固定大小缩放
            be = (int) (newOpts.outHeight / hh);
        }
        if (be <= 0)
            be = 1;
        newOpts.inSampleSize = be;// 设置缩放比例
        // 重新读入图片，注意此时已经把options.inJustDecodeBounds 设回false了
        isBm = new ByteArrayInputStream(baos.toByteArray());
        bitmap = BitmapFactory.decodeStream(isBm, null, newOpts);
        return compressImage(bitmap);// 压缩好比例大小后再进行质量压缩
    }

    // 把bitmap转换成String
    public static String bitmapToString(String filePath) {
        Bitmap bm = getSmallBitmap(filePath);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        bm.compress(Bitmap.CompressFormat.JPEG, 40, baos);
        byte[] b = baos.toByteArray();
        return Base64.encodeToString(b, Base64.DEFAULT);
    }

    /**
     *  质量压缩
     * @param image
     * @return
     */
    public static Bitmap compressImage(Bitmap image) {

        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        image.compress(Bitmap.CompressFormat.JPEG, 50, baos);// 质量压缩方法，这里100表示不压缩，把压缩后的数据存放到baos中
        int options = 50;
        while (baos.toByteArray().length / 1024 > 100) { // 循环判断如果压缩后图片是否大于100kb,大于继续压缩
            baos.reset();// 重置baos即清空baos
            image.compress(Bitmap.CompressFormat.JPEG, options, baos);// 这里压缩options%，把压缩后的数据存放到baos中
            options -= 10;// 每次都减少10
        }
        ByteArrayInputStream isBm = new ByteArrayInputStream(baos.toByteArray());// 把压缩后的数据baos存放到ByteArrayInputStream中
        Bitmap bitmap = BitmapFactory.decodeStream(isBm, null, null);// 把ByteArrayInputStream数据生成图片
        return bitmap;
    }

    /**
     * 根据Uri获取图片绝对路径，解决Android4.4以上版本Uri转换
     * @param context
     * @param imageUri
     * @author yaoxing
     * @date 2014-10-12
     */
    public static String getImageAbsolutePath(Activity context, Uri imageUri) {
        if (context == null || imageUri == null)
            return null;
        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.KITKAT && DocumentsContract.isDocumentUri(context, imageUri)) {
            if (isExternalStorageDocument(imageUri)) {
                String docId = DocumentsContract.getDocumentId(imageUri);
                String[] split = docId.split(":");
                String type = split[0];
                if ("primary".equalsIgnoreCase(type)) {
                    return Environment.getExternalStorageDirectory() + "/" + split[1];
                }
            } else if (isDownloadsDocument(imageUri)) {
                String id = DocumentsContract.getDocumentId(imageUri);
                Uri contentUri = ContentUris.withAppendedId(Uri.parse("content://downloads/public_downloads"), Long.valueOf(id));
                return getDataColumn(context, contentUri, null, null);
            } else if (isMediaDocument(imageUri)) {
                String docId = DocumentsContract.getDocumentId(imageUri);
                String[] split = docId.split(":");
                String type = split[0];
                Uri contentUri = null;
                if ("image".equals(type)) {
                    contentUri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
                } else if ("video".equals(type)) {
                    contentUri = MediaStore.Video.Media.EXTERNAL_CONTENT_URI;
                } else if ("audio".equals(type)) {
                    contentUri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
                }
                String selection = MediaStore.Images.Media._ID + "=?";
                String[] selectionArgs = new String[] { split[1] };
                return getDataColumn(context, contentUri, selection, selectionArgs);
            }
        } // MediaStore (and general)
        else if ("content".equalsIgnoreCase(imageUri.getScheme())) {
            // Return the remote address
            if (isGooglePhotosUri(imageUri))
                return imageUri.getLastPathSegment();
            return getDataColumn(context, imageUri, null, null);
        }
        // File
        else if ("file".equalsIgnoreCase(imageUri.getScheme())) {
            return imageUri.getPath();
        }
        return null;
    }

    public static String getDataColumn(Context context, Uri uri, String selection, String[] selectionArgs) {
        Cursor cursor = null;
        String column = MediaStore.Images.Media.DATA;
        String[] projection = { column };
        try {
            cursor = context.getContentResolver().query(uri, projection, selection, selectionArgs, null);
            if (cursor != null && cursor.moveToFirst()) {
                int index = cursor.getColumnIndexOrThrow(column);
                return cursor.getString(index);
            }
        } finally {
            if (cursor != null)
                cursor.close();
        }
        return null;
    }

    /***
     * 图片的缩放方法
     *
     * @param bgimage
     *            ：源图片资源
     * @param newWidth
     *            ：缩放后宽度
     * @param newHeight
     *            ：缩放后高度
     * @return
     */
    public static Bitmap zoomImage(Bitmap bgimage, double newWidth,
                                   double newHeight) {
        // 获取这个图片的宽和高
        float width = bgimage.getWidth();
        float height = bgimage.getHeight();
        // 创建操作图片用的matrix对象
        Matrix matrix = new Matrix();
        // 计算宽高缩放率
        float scaleWidth = ((float) newWidth) / width;
        float scaleHeight = ((float) newHeight) / height;
        // 缩放图片动作
        matrix.postScale(scaleWidth, scaleHeight);
        Bitmap bitmap = Bitmap.createBitmap(bgimage, 0, 0, (int) width,
                (int) height, matrix, true);
        return bitmap;
    }

    /**
     * @param uri The Uri to check.
     * @return Whether the Uri authority is ExternalStorageProvider.
     */
    public static boolean isExternalStorageDocument(Uri uri) {
        return "com.android.externalstorage.documents".equals(uri.getAuthority());
    }

    /**
     * @param uri The Uri to check.
     * @return Whether the Uri authority is DownloadsProvider.
     */
    public static boolean isDownloadsDocument(Uri uri) {
        return "com.android.providers.downloads.documents".equals(uri.getAuthority());
    }

    /**
     * @param uri The Uri to check.
     * @return Whether the Uri authority is MediaProvider.
     */
    public static boolean isMediaDocument(Uri uri) {
        return "com.android.providers.media.documents".equals(uri.getAuthority());
    }

    /**
     * @param uri The Uri to check.
     * @return Whether the Uri authority is Google Photos.
     */
    public static boolean isGooglePhotosUri(Uri uri) {
        return "com.google.android.apps.photos.content".equals(uri.getAuthority());
    }
}

BitmapUtil工具类主要包含了获取bitmap、质量压缩等一些方法。当然拍照之后一般会获取图片的base64，然后上传给服务端，或者前端js。 `BitmapToBase64Util`代码如下；

`BitmapToBase64Util`

public class BitmapToBase64Util {
    /**
     * bitmapתΪbase64
     *
     * @param bitmap
     * @return
     */
    public static String bitmapToBase64(Bitmap bitmap) {

        String result = null;
        ByteArrayOutputStream baos = null;
        try {
            if (bitmap != null) {
                baos = new ByteArrayOutputStream();
                bitmap.compress(Bitmap.CompressFormat.JPEG, 50, baos);  //这里50表示压缩50%
                baos.flush();
                baos.close();
                byte[] bitmapBytes = baos.toByteArray();
                result = Base64.encodeToString(bitmapBytes, Base64.DEFAULT);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (baos != null) {
                    baos.flush();
                    baos.close();
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return result;
    }

    /**
     * base64תΪbitmap
     *
     * @param base64Data
     * @return
     */
    public static Bitmap base64ToBitmap(String base64Data) {
        byte[] bytes = Base64.decode(base64Data, Base64.DEFAULT);
        return BitmapFactory.decodeByteArray(bytes, 0, bytes.length);
    }
}

关于调用系统相机、拍照上传就到处为止，希望能帮助到一些需要帮助的人