写项目的时候一般都会用到头像选择功能，现在整理一下.

需求： 头像选择需要有两个选项：

1. 从手机拍照获取；
2. 从相册中获取。

效果如下：

这里写图片描述

Demo地址：https://github.com/KeithLanding/ImagePicker

关键代码：

一. 调起相册

     public void selectImage() {
        Intent intent = new Intent(Intent.ACTION_PICK);
        intent.setType("image/*");
        //判断系统中是否有处理该Intent的Activity
        if (intent.resolveActivity(getPackageManager()) != null) {
            startActivityForResult(intent, REQUEST_IMAGE_GET);
        } else {
            showToast("未找到图片查看器");
        }
    }

二. 调起相机

    private void dispatchTakePictureIntent() {
        Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
        // 判断系统中是否有处理该Intent的Activity
        if (intent.resolveActivity(getPackageManager()) != null) {
            // 创建文件来保存拍的照片
            File photoFile = null;
            try {
                photoFile = createImageFile();
            } catch (IOException ex) {
                // 异常处理
            }
            if (photoFile != null) {
                intent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(photoFile));
                startActivityForResult(intent, REQUEST_IMAGE_CAPTURE);
            }
        } else {
            showToast("无法启动相机");
        }
    }
    /**
     * 创建新文件
     *
     * @return
     * @throws IOException
     */
    private File createImageFile() throws IOException {
        String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
        String imageFileName = "JPEG_" + timeStamp + "_";
        File storageDir = Environment.getExternalStoragePublicDirectory
        (Environment.DIRECTORY_PICTURES);
        File image = File.createTempFile(
                imageFileName,  /* 文件名 */
                ".jpg",         /* 后缀 */
                storageDir      /* 路径 */
        );
        mCurrentPhotoPath = image.getAbsolutePath();
        return image;
    }

三. 处理返回结果

    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        // 回调成功
        if (resultCode == RESULT_OK) {
            String filePath = null;
            //判断是哪一个的回调
            if (requestCode == REQUEST_IMAGE_GET) {
                //返回的是content://的样式
                filePath = getFilePathFromContentUri(data.getData(), this);
            } else if (requestCode == REQUEST_IMAGE_CAPTURE) {
                if (mCurrentPhotoPath != null) {
                    filePath = mCurrentPhotoPath;
                }
            }
            if (!TextUtils.isEmpty(filePath)) {
                // 自定义大小，防止OOM
                Bitmap bitmap = getSmallBitmap(filePath, 200, 200);
                mAvatar.setImageBitmap(bitmap);
            }
        }
    }
    /**
     * @param uri     content:// 样式
     * @param context
     * @return real file path
     */
    public static String getFilePathFromContentUri(Uri uri, Context context) {
        String filePath;
        String[] filePathColumn = {MediaStore.MediaColumns.DATA};
        Cursor cursor = context.getContentResolver().query(uri, filePathColumn, null, null, null);
        if (cursor == null) return null;
        cursor.moveToFirst();
        int columnIndex = cursor.getColumnIndex(filePathColumn[0]);
        filePath = cursor.getString(columnIndex);
        cursor.close();
        return filePath;
    }
    /**
     * 获取小图片，防止OOM
     *
     * @param filePath
     * @param reqWidth
     * @param reqHeight
     * @return
     */
    public static Bitmap getSmallBitmap(String filePath, int reqWidth, int reqHeight) {
        final BitmapFactory.Options options = new BitmapFactory.Options();
        options.inJustDecodeBounds = true;
        try {
            BitmapFactory.decodeFile(filePath, options);
        } catch (Exception e) {
            e.printStackTrace();
        }
        options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
        options.inJustDecodeBounds = false;
        return BitmapFactory.decodeFile(filePath, options);
    }
    /**
     * 计算图片缩放比例
     *
     * @param options
     * @param reqWidth
     * @param reqHeight
     * @return
     */
    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;
    }

注意事项：

• 读写权限要加上：

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

• 调起相册时，Intent用的Action是Intent.ACTION_PICK,而不是 ACTION_GET_CONTENT，使用后者返回uri在android 4.4及以上和以下会有不同，要分开处理。