//检查权限
    public void checkPermission() {
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);
            //发现没有权限，调用requestPermissions方法向用户申请权限，requestPermissions接收三个参数，第一个是context，第二个是一个String数组，我们把要申请的权限
            //名放在数组中即可，第三个是请求码，只要是唯一值就行
        } else {
            openAlbum();//有权限就打开相册
        }
    }

    public void openAlbum() {
        //通过intent打开相册，使用startactivityForResult方法启动actvity，会返回到onActivityResult方法，所以我们还得复写onActivityResult方法
        Intent intent = new Intent("android.intent.action.GET_CONTENT");
        intent.setType("image/*");
        startActivityForResult(intent, CHOOSE_PHOTO);
    }
    //弹出窗口向用户申请权限


    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);//弹出授权的窗口，这条语句也可以删除，没有影响
        //获得了用户的授权结果，保存在grantResults中，判断grantResult中的结果来决定接下来的操作
        switch (requestCode) {
            case 1:

                if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    openAlbum();
                } else {
                    Toast.makeText(this, "授权失败，无法操作", Toast.LENGTH_SHORT).show();
                }
                break;
            default:
                break;
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        switch (requestCode) {
            case CHOOSE_PHOTO:
                if (resultCode == RESULT_OK) {
                    if (Build.VERSION.SDK_INT >= 19) {
                        handleImageOnkitKat(data);//高于4.4版本使用此方法处理图片
                    } else {
                        handleImageBeforeKitKat(data);//低于4.4版本使用此方法处理图片
                    }
                }
                break;
            default:
                break;
        }
    }

    @TargetApi(19)
    private void handleImageOnkitKat(Intent data) {
        String imagePath = null;
        Uri uri = data.getData();
        if (DocumentsContract.isDocumentUri(this, uri)) {
            //如果是document类型的uri，则通过document id处理
            String docId = DocumentsContract.getDocumentId(uri);
            if ("com.android.providers.media.documents".equals(uri.getAuthority())) {
                String id = docId.split(":")[1];//解析出数字格式的id
                String selection = MediaStore.Images.Media._ID + "=" + id;
                imagePath = getImagePath(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, selection);
            } else if ("com.android,providers.downloads.documents".equals(uri.getAuthority())) {
                Uri contentUri = ContentUris.withAppendedId(Uri.parse("content://downloads/public_downloads"), Long.valueOf(docId));
                imagePath = getImagePath(contentUri, null);
            }

        } else if ("content".equalsIgnoreCase(uri.getScheme())) {
            imagePath = getImagePath(uri, null);
        }
        displayImage(imagePath);
    }

    private void handleImageBeforeKitKat(Intent data) {
        Uri uri = data.getData();
        String imagePath = getImagePath(uri, null);
        displayImage(imagePath);
    }

    //获得图片路径
    public String getImagePath(Uri uri, String selection) {
        String path = null;
        Cursor cursor = getContentResolver().query(uri, null, selection, null, null);   //内容提供器
        if (cursor != null) {
            if (cursor.moveToFirst()) {
                path = cursor.getString(cursor.getColumnIndex(MediaStore.Images.Media.DATA));   //获取路径
            }
        }
        cursor.close();
        return path;
    }

    //展示图片
    private void displayImage(String imagePath) {
        if (imagePath != null) {
            Bitmap bitImage = BitmapFactory.decodeFile(imagePath);//格式化图片

            mImage.setImageBitmap(bitImage);//为imageView设置图片

        } else {
            Toast.makeText(MainActivity.this, "获取图片失败", Toast.LENGTH_SHORT).show();
        }
    }