java由于mkdirs（）的原因，我无法在外部目录中备份我的领域数据库

Question

我正在尝试将我的领域数据库导出到外部存储中（实际上是在我的手机中）

当我按下下面的按钮时，名为backupRealmNow()的方法可以工作

public void backupRealmNow() {

    Realm nowRealmForBackup = Realm.getDefaultInstance();

    String filePath = "";

    try {
        File dir = new File(Environment.DIRECTORY_DOWNLOADS);
        File exportRealmFile = new File(Environment.DIRECTORY_DOWNLOADS, "backup.realm");
        filePath = exportRealmFile.getPath();

        if(!dir.exists()) {
            dir.mkdirs();
        }

        if(!exportRealmFile.exists()) {
            exportRealmFile.mkdirs();
            Log.d("Path", "mkdirs :: " + filePath);
        }

        if(exportRealmFile.exists()) {
            exportRealmFile.delete();
            nowRealmForBackup.writeCopyTo(exportRealmFile);
            Log.d("Backup", "Success to backup " + filePath);
        } else {
            Log.d("Backup", "Failed to Backup");
        }

    } catch(Exception e) {
        e.printStackTrace();
    } finally {
        String msg =  "File exported to Path: " + filePath;
        Toast.makeText(getActivity().getApplicationContext(), msg, Toast.LENGTH_LONG).show();
        Log.d(TAG, msg);

        nowRealmForBackup.close();
    }

}

当我运行上述代码时，我的logcat说

D/Path: mkdirs :: Download/backup.realm
D/Backup: Failed to Backup
D/ContentValues: File exported to Path: Download/backup.realm

我搜索了一段时间不起作用的原因，所以我检查了权限（因为我的手机运行在SDK 23 Marshmellow中），但是，我的权限被授予了。下面的代码正在检查MainActivity.java中的权限

if (ActivityCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED
            && ActivityCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
        ActivityCompat.requestPermissions(this
                , new String[]{安卓.Manifest.permission.WRITE_EXTERNAL_STORAGE, 安卓.Manifest.permission.READ_EXTERNAL_STORAGE}
                , REQUEST_RWAVAILABLE);
    } else {
        Log.e("Read and Write", "PERMISSION GRANTED");
    }

我的logcat说“允许”

我认为问题是exportRealmFile.mkdirs()不起作用。你知道原因吗？（正如您在日志中看到的那样，Logcat在该代码处没有任何异常”

========= 编辑：backupRealmNow()已更改为检查是否允许使用我的包

public void backupRealmNow() {

    Realm nowRealmForBackup = Realm.getDefaultInstance();

    int REQUESTCODE_WRITE = 100;
    int REQUESTCODE_READ = 200;

    String filePath = "";

    try {
        File dir = new File(Environment.DIRECTORY_DOWNLOADS);
        File exportRealmFile = new File(Environment.DIRECTORY_DOWNLOADS, "backup.realm");
        filePath = exportRealmFile.getPath();

        if(!dir.exists()) {
            dir.mkdirs();
        }

        if(!exportRealmFile.exists()) {
            exportRealmFile.mkdirs();
            if(exportRealmFile.exists()) {
                Log.d("mkdirs", "Success to make dir");
            } else {
                Log.d("mkdirs", "Failed to make dir");
                if(PermissionChecker.checkSelfPermission(getActivity().getApplicationContext(), Manifest.permission.WRITE_EXTERNAL_STORAGE) != PermissionChecker.PERMISSION_GRANTED) {
                    Log.e("PermissionChecker", "WRITE_EXTERNAL_STORAGE PERMISSION_DENIED so request.");
                    requestPermissions(new String[] {Manifest.permission.WRITE_EXTERNAL_STORAGE}, REQUESTCODE_WRITE);
                } else {
                    Log.e("PermissionChecker", "WRITE_EXTERNAL_STORAGE PERMISSION_GRANTED");

                }
                if(PermissionChecker.checkSelfPermission(getActivity().getApplicationContext(), Manifest.permission.READ_EXTERNAL_STORAGE) != PermissionChecker.PERMISSION_GRANTED) {
                    Log.e("PermissionChecker", "READ_EXTERNAL_STORAGE PERMISSION_DENIED so request.");
                    requestPermissions(new String[] {Manifest.permission.READ_EXTERNAL_STORAGE}, REQUESTCODE_READ);
                } else {
                    Log.e("PermissionChecker", "READ_EXTERNAL_STORAGE PERMISSION_GRANTED");
                }
            }
        }

        if(exportRealmFile.exists()) {
            exportRealmFile.delete();
            nowRealmForBackup.writeCopyTo(exportRealmFile);
            Log.d("Backup", "Success to backup " + filePath);
        } else {
            Log.d("Backup", "Failed to Backup");
        }

    } catch(Exception e) {
        e.printStackTrace();
    } finally {
        String msg =  "File exported to Path: " + filePath;
        Toast.makeText(getActivity().getApplicationContext(), msg, Toast.LENGTH_LONG).show();
        Log.d(TAG, msg);

        nowRealmForBackup.close();
    }

}

我的logcat说

D/mkdirs: Failed to make dir
E/PermissionChecker: WRITE_EXTERNAL_STORAGE PERMISSION_GRANTED
E/PermissionChecker: READ_EXTERNAL_STORAGE PERMISSION_GRANTED
D/Backup: Failed to Backup
D/ContentValues: File exported to Path: Download/backup.realm

Answer 1

看看情况

ActivityCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED
        && 
ActivityCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED

即使WRITE_EXTERNAL_STORAGE被拒绝，并且不能保证会请求此权限，也可以false这样做

尝试将和运算符更改为或，以真正了解WRITE_EXTERNAL_STORAGE是否被授予。或者，您可以相互独立地检查和请求权限

Answer 2

您正试图在根目录（“/”）中创建目录“下载”。您需要使用Environment.getExternalStoragePublicDirectory来获取公共存储区域的路径，在那里您可以实际创建文件和目录