getExternalCacheDir（）返回清除数据后空 [英] getExternalCacheDir() returns null after clearing data

问题描述

我有访问和写入数据到外部存储一个简单的应用程序。一切工作正常，直到我进入设置 - >应用程序 - >应用信息，并通过清除数据按钮清晰的数据， 然后每次调用 getExternalCacheDir（）开始返回null。

I have a simple app that access and writes data to external storage. Everything works fine until I go to Settings -> Apps -> App Info and clear data via "Clear data" button, then every call to getExternalCacheDir() starts returning null.

我一直在开发上的Nexus 7运行Android 4.2.2。

I have been developing on Nexus 7 running Android 4.2.2.

我的表现是这样的：

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.package"
    android:versionCode="5"
    android:versionName="1.3"
    xmlns:tools="http://schemas.android.com/tools">

<uses-sdk
    android:minSdkVersion="8"
    android:targetSdkVersion="17" />

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

<application
...

code段不工作：

Code snippet that does not work:

    Log.d(TAG, "getExternalStorageState() = " + Environment.getExternalStorageState());
    Log.d(TAG, "getExternalCacheDir() = " + c.getExternalCacheDir());
    Log.d(TAG, "getExternalFilesDir(null) = " + c.getExternalFilesDir(null));
    Log.d(TAG, "getExternalFilesDir(Environment.DIRECTORY_MOVIES) = " + c.getExternalFilesDir(Environment.DIRECTORY_MOVIES));

应用程序被安装并执行后LogCat中：

LogCat after the app is installed and executed:

05-15 11:26:45.948: DEBUG/HelperUtils(5541): getExternalStorageState() = mounted
05-15 11:26:45.948: DEBUG/HelperUtils(5541): getExternalCacheDir() =     /storage/emulated/0/Android/data/com.example.package/cache
05-15 11:26:45.948: DEBUG/HelperUtils(5541): getExternalFilesDir(null) = /storage/emulated/0/Android/data/com.example.package/files
05-15 11:26:45.948: DEBUG/HelperUtils(5541): getExternalFilesDir(Environment.DIRECTORY_MOVIES) = /storage/emulated/0/Android/data/com.example.package/files/Movies

在应用信息设置清除数据后LogCat中：

LogCat after clearing data in App Info settings:

05-15 11:27:57.848: DEBUG/HelperUtils(5859): getExternalStorageState() = mounted
05-15 11:27:57.848: WARN/ContextImpl(5859): Unable to create external cache directory
05-15 11:27:57.848: DEBUG/HelperUtils(5859): getExternalCacheDir() = null
05-15 11:27:57.848: WARN/ContextImpl(5859): Unable to create external files directory
05-15 11:27:57.848: DEBUG/HelperUtils(5859): getExternalFilesDir(null) = null
05-15 11:27:57.848: WARN/ContextImpl(5859): Unable to create external files directory
05-15 11:27:57.848: DEBUG/HelperUtils(5859): getExternalFilesDir(Environment.DIRECTORY_MOVIES) = null
05-15 11:27:57.848: WARN/ContextImpl(5859): Unable to create external cache directory

在清理数据和执行应用程序 getExternalCacheDir（）返回null即使 Environment.getExternalStorageState（）返回安装。有谁知道什么可能是可能是错的？

After clearing data and executing the app getExternalCacheDir() method returns null even though Environment.getExternalStorageState() returns "mounted". Does anyone know what could be possibly wrong?

修改

通过从Gjordis的帮助下我已经发现了的清除数据的按钮，删除整个应用程序的临时目录：

With the help from Gjordis I have found out that Clear data button removes whole application temporary directory:

存储/ sdcard0 /安卓/数据/ com.example.app /缓存在的Andr​​oid /数据

和我是不是能够通过 getExternalCacheDir（）或手动重新创建它（尽管我可以在存储/ sdcard0创建其他目录/安卓/数据/ ）。

and I was not able to create it again via getExternalCacheDir() or manually (though I am able to create other directories under storage/sdcard0/Android/data/).

（的Andr​​oid /数据/ com.example.app <​​/ code>再次创建设备重新启动后，但是这不是我要找的解决方案）

(Android/data/com.example.app is created again after the device is rebooted, but that is not the solution I am looking for)

推荐答案

我也遇到和解决了这个确切的问题。点击清除数据按钮，使机器人停止你的应用程序停止运行，删除整个应用程序特定的文件夹MNT / SD卡/安卓/数据/ your.package.name。不过，我有一个从调用Runtime.getRuntime（）启动一个单独的进程。EXEC（）这是仍在运行，它被写入该文件夹。这导致被卡在锁定状态的文件夹，并造成你描述的时候，我的应用程序称为getExternalCacheDir（）相同的症状。运行亚行外壳然后 LS 从/ mnt / SD卡/安卓/ data文件夹中显示该文件夹被锁定通过一个过程。运行 PS 显示，我的其他程序仍在运行。

I have encountered and solved this exact problem. Clicking the Clear Data button causes Android to stop your app from running and delete the entire application-specific folder "mnt/sdcard/Android/data/your.package.name". However, I had a separate process that was started from Runtime.getRuntime().exec() that was still running and it was writing to this folder. This caused the folder to be stuck in a locked state and caused the same symptom you described when my app called getExternalCacheDir(). Running adb shell and then ls from within the /mnt/sdcard/Android/data folder showed that the folder was locked by a process. Running ps showed that my other process was still running.

解决的办法是在调用getExternalCacheDir（）。

The solution was to properly kill the other process that was still writing to my application's application-specific folder before calling getExternalCacheDir().

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