Can you write to the sdcard folder when there is no sdcard?

问题

So I'm testing an app on a galaxy s3 on 4.1 and an older phone that runs 2.3. Neither phone has an sdcard in it but when I use Environment.getExternalStorageDirectory().getAbsolutePath() on my galaxy s3 it directs me to a folder called sdcard0 within a folder called storage. When I run it on the older phone it gives me the path mnt/sdcard/ and the sdcard folder is read only.

I am trying to create a folder in these directories. I can do it on my s3 but not on my older phone.

Is there something similar to the storage folder I'm missing on the older phone or can I write to the sdcard folder when there is no sd card present?

EDIT: I have the external write permissions in my manifest

回答1:

On some phones, as the documentation suggests, the word external is not to be taken all too serious:

Note: don't be confused by the word "external" here. This directory can better be thought as media/shared storage. It is a filesystem that can hold a relatively large amount of data and that is shared across all applications (does not enforce permissions). Traditionally this is an SD card, but it may also be implemented as built-in storage in a device that is distinct from the protected internal storage and can be mounted as a filesystem on a computer.

You can check if the storage is really external or not, using the Environment.isExternalStorageRemovable()-method. If it's not removable, you should always be able to write to it (given that you have the permissions declared).

If it is however removable, you'll need to check it's current state with Environment.getExternalStorageState(). Here's a quick example of how to use it:

String state = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED.equals(state)) {
    // We can read and write!
} else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
    // Mounted read only...
} else {
    // Something is wrong...
}

So in these cases, you can write to the external storage.

Important: As the documentation specifies at multiple points, the above methods work for the primary external storage. Some devices (like the Motorola Xoom) have both an internal "external" storage, and an SD-Card.

There seems to be no "generalized" way to access the "secondary external storage" on such devices, although there is a standard now, introduced with Android 4.2

Devices may contain multiple instances of external storage, but currently only the primary external storage is exposed to developers through API.

[...]

Starting in Android 4.2, devices can support multiple users, and external storage must meet the following constraints:

[...]

Secondary external storage must not be writable by apps.

It seems to depend on the vendor which storage (internal or real external) is considered the primary one. Not much you can do here (without things getting messy...)

If there is no external storage present, you can use your applications Internal Storage, or the caching directory, depending on what kind of data you're storing.

来源：https://stackoverflow.com/questions/16492087/can-you-write-to-the-sdcard-folder-when-there-is-no-sdcard

标签

android

sd-card