Question

当我使用调试器时，sd.canWrite（）语句返回false并且不运行其余代码。我尝试使用模拟器和实际的三星平板电脑。我有

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

在我的清单中。

public void exportDatabse(String databaseName) {
        try {
            File sd = Environment.getExternalStorageDirectory();

            File data = Environment.getDataDirectory();


            if (sd.canWrite()) {
                String currentDBPath = "//data//"+getPackageName()+"//databases//"+databaseName+"";
                String backupDBPath = "backupname.db";
                File currentDB = new File(data, currentDBPath);
                File backupDB = new File(sd, backupDBPath);
                Log.d("file", "file copied2");

                if (currentDB.exists()) {
                    FileChannel src = new FileInputStream(currentDB).getChannel();
                    FileChannel dst = new FileOutputStream(backupDB).getChannel();
                    dst.transferFrom(src, 0, src.size());
                    src.close();
                    dst.close();
                }
                Log.d("file", "file copied3");
            }
        } catch (Exception e) {
            Log.d("file", "file not copied");

        }
        Log.d("file", "method runs");
    }

Answer 1

请检查外部存储器是否写保护 -

String state = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {

}

Answer 2

如果您使用的是在Android 6.0或更高版本上运行的模拟器或系统您必须为Critical or Dangerous Permissions添加运行时权限

确保您的活动实施OnRequestPermissionResult。然后做

boolean permission = isStoragePermissionGranted();
if(permission){
     //DO YOUR TASK HERE
}

public  boolean isStoragePermissionGranted() {
    if (Build.VERSION.SDK_INT >= 23) {
        if (checkSelfPermission(android.Manifest.permission.WRITE_EXTERNAL_STORAGE)
                == PackageManager.PERMISSION_GRANTED) {
            Log.v(TAG,"Permission is granted");
            return true;
        } else {
            Log.v(TAG,"Permission is revoked");
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);
            return false;
        }
    }
    else { //permission is automatically granted on sdk<23 upon installation
        Log.v(TAG,"Permission is granted");
        return true;
    }
}

回调功能

@Override
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
    super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    if(grantResults[0]== PackageManager.PERMISSION_GRANTED){
        Log.v(TAG,"Permission: "+permissions[0]+ "was "+grantResults[0]);
        //resume tasks needing this permission
    }
}

Refer This to know more

canWrite（）到SD返回false

2 个答案: