Emulator上的存储写入

Question

我正在使用android Studio 3.6的模拟器开发android应用程序。我正在使用Nexus 7的虚拟设备和安卓10。

我已授予清单文件的权限，并要求用户授予对外部存储的读写权限。

虽然权限可以，但我无法在外部存储上创建文件夹。我试着在后台写作。

这是清单文件的摘录

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

这是我的主活动的摘录，我在其中请求用户给予权限并调用后台进程：UnitDataUpdater

public class MainActivity extends AppCompatActivity {
public static final String EXTRA_MESSAGE = "com.example.myfirstapp.MESSAGE";
public static final int MY_PERMISSIONS_REQUEST_EXTERNAL_STORAGE = 1;
// public static String SERVER_API_URL =  "http://local.xxxx.xxxxx.eu/index.php?option=com_alumincocc&view=examlist&Itemid=122&format=json&unitCode=";
// public static LinearLayout examList;
public JSONArray uiData;
ListView examsList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
checkPermissions();
setContentView(R.layout.activity_main);
String url = "http://xxxxx.xxxxx.eu/index.php?option=com_alumincocc&view=examlist&Itemid=122&format=json&unitCode=478050";
String result = "";
examsList = (ListView) findViewById(R.id.examsList);
UnitDataUpdater process = new UnitDataUpdater(this);
try {
result = process.execute(url).get();
} catch (ExecutionException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
........

public void checkPermissions() {
if (ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE)
!= PackageManager.PERMISSION_GRANTED
||
ContextCompat.checkSelfPermission(this, Manifest.permission.READ_EXTERNAL_STORAGE)
!= PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(MainActivity.this,
new String[]{Manifest.permission.READ_EXTERNAL_STORAGE, Manifest.permission.WRITE_EXTERNAL_STORAGE},
MY_PERMISSIONS_REQUEST_EXTERNAL_STORAGE);
}
}
@Override
public void onRequestPermissionsResult(int requestCode,
@NonNull String[] permissions,
@NonNull int[] grantResults) {
super
.onRequestPermissionsResult(requestCode,
permissions,
grantResults);
if (requestCode == MY_PERMISSIONS_REQUEST_EXTERNAL_STORAGE) {
// Checking whether user granted the permission or not.
if (grantResults.length > 0
&& grantResults[0] == PackageManager.PERMISSION_GRANTED) {
// Showing the toast message
Toast.makeText(MainActivity.this,
"Write Permission Granted",
Toast.LENGTH_SHORT)
.show();
} else {
Toast.makeText(MainActivity.this,
"Write Permission Denied",
Toast.LENGTH_SHORT)
.show();
}
}
}
}

这是我尝试写入外部存储器的后台过程。getAppDi方法是我尝试创建新文件夹的地方。这个文件夹从未创建过，所以类的其他部分会抛出错误。

奇怪的是，在模拟器上我看不到Document文件夹。我在下载文件夹上尝试过同样的东西，但仍然是一样的。

public class UnitDataUpdater extends AsyncTask<String, Void, String> {
//  private static String REMOTE_URL = "http://local.xxxxxx.xxxxx.eu/index.php?option=com_alumincocc&view=examlist&Itemid=122&format=json&unitCode=";
private String data = "";
public static final String REQUEST_METHOD = "GET";
public static final int READ_TIMEOUT = 15000;
public static final int CONNECTION_TIMEOUT = 15000;
private String filePrefix = "i";
private MainActivity mainActivity;
public UnitDataUpdater(Activity mainActivity) {
this.mainActivity = (MainActivity) mainActivity;
}
........
private String getAppDir() {
String externalStoragePublicDirectory = Environment
.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS)
.getAbsolutePath();

String appDirPath = externalStoragePublicDirectory + "/XXXXUnitData";
File appDir = new File(appDirPath);
if (!appDir.exists()) {
if (!appDir.mkdir()) {
try {
throw new Exception("Storage Error");
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
}
return appDir.getAbsolutePath();
}
}

感谢提供的任何帮助

Answer 1

在Android Q上，外部存储不可读写。请改用getExternalFilesDir(null(。在清单或运行时，您不需要任何读写权限。