解决万恶的open failed: ENOENT (No such file or directory)/(Operation not permitted)

一、Android 11上传下载资源失败：open failed: ENOENT (No such file or directory)

前提：发现Android 11 上传图片及下载文件都失败，报错日志：open failed: ENOENT (No such file or directory)

原来是Android 11访问文件资源管理器需要加上特殊权限：MANAGE_EXTERNAL_STORAGE 文件管理权限
之前申请权限是通过Dialog展现给用户，而Android 11以后通过 Activity 展现给用户看(Intent跳转)。

1）目标sdk修改为30：targetSdkVersion 30
2）清单文件注册：

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

3）当系统在11及以上申请此权限

	 public void checkPermissions() {
    
	        //申请危险权限
	        ....
	        //申请Android11特殊权限
	        requestManagerPermission();
	 }

    private void requestManagerPermission() {
    
    	//当系统在11及以上
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
    
            // 没文件管理权限时申请权限
            if (!Environment.isExternalStorageManager()) {
    
                Intent intent = new Intent(Settings.ACTION_MANAGE_APP_ALL_FILES_ACCESS_PERMISSION);
                intent.setData(Uri.parse("package:" + mContext.getPackageName()));
                startActivityForResult(intent, REQUEST_MANAGER_PERMISSION);
            }
        }
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
    
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == REQUEST_MANAGER_PERMISSION && Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
    
        	//用户拒绝权限，重新申请
            if (!Environment.isExternalStorageManager()) {
    
                requestManagerPermission();
            }
        }
    }

二、保存截图失败：open failed: EPERM (Operation not permitted)

前提：发现Android 11 保存截图失败，报错日志：open failed: ENOENT (Operation not permitted)

解决：根据版本，将文件保存在不同的路径下。
默认获取外部存储目录，sdk>29获取外部SD卡缓存目录。

String path = Environment.getExternalStorageDirectory().getPath();
if (Build.VERSION.SDK_INT > 29) {
    
	path = activity.getExternalFilesDir(null).getAbsolutePath() ;
}
File file = new File(path, fileName);
//截图流程...请忽略
try {
    
      BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(file));
      // 截屏-将view作为原图绘制出来
      View v = activity.getWindow().getDecorView();
      Bitmap bitmap = Bitmap.createBitmap(v.getWidth(), v.getHeight(),Bitmap.Config.RGB_565);
      Canvas c = new Canvas(bitmap);
      c.translate(-v.getScrollX(), -v.getScrollY());
      v.draw(c);
      // 压缩Bitmap,不支持png图片的压缩
      bitmap.compress(Bitmap.CompressFormat.JPEG, 100, bos);
      bos.flush();
      bos.close();
      // 把文件插入到系统图库
      ContentValues values = new ContentValues();
      values.put(MediaStore.Images.Media.DATA, file.getAbsolutePath());
      values.put(MediaStore.Images.Media.MIME_TYPE, "image/jpeg");
      Uri uri =activity.getContentResolver().insert(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, values);
      // 通知图库更新
      activity.sendBroadcast(newIntent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, Uri.fromFile(file)));
      ToastUtils.showMessage("保存成功");
} catch (IOException e) {
    
	  e.printStackTrace();
	  ToastUtils.showMessage(e.getMessage());
}

参考：https://blog.csdn.net/dongxianfei/article/details/115449709
https://zhuanlan.zhihu.com/p/477539888