android - 如何在Android的SD卡中创建文件夹

我想在sdcard中创建文件夹，并且使用了以下代码:

public class Screen extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.welcome);

        operateOnFirstUsage();
    }

    private void operateOnFirstUsage() {

        String state = Environment.getExternalStorageState();
        Log.d("Media State", state);

        if (Environment.MEDIA_MOUNTED.equals(state)) {
            File appDirectory = new File(
                    Environment.getExternalStorageDirectory().getAbsolutePath() + "/MyApp/");

            Log.d("appDirectroyExist", appDirectory.exists() + "");
            if (!appDirectory.exists())
                Log.d("appDir created: ", appDirectory.mkdir() + "");

            File dbDirectory = new File(
                    Environment.getExternalStorageDirectory().getAbsolutePath() + "/MyApp/Database/");

            Log.d("dbDirectroyExist", dbDirectory.exists() + "");
            if (!dbDirectory.exists())
                Log.d("dbDir created: ", dbDirectory.mkdirs() + "");


            File themesDirectory = new File(
                    Environment.getExternalStorageDirectory().getAbsolutePath() + "/MyApp/Themes/");
            Log.d("themesDirectroyExist", themesDirectory.exists() + "");
            if (!themesDirectory.exists())
                Log.d("themesDir created: ", themesDirectory.mkdirs() + "");

        }
    }
}

另外，我还设置了sdcard写权限:

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

我已经多次运行该应用程序，并且每次获得LogCat输出时:

01-09 21:38:13.701: D/Media State(15363): mounted
01-09 21:38:13.701: D/appDirectroyExist(15363): false
01-09 21:38:13.701: D/appDir created:(15363): false
01-09 21:38:13.701: D/dbDirectroyExist(15363): false
01-09 21:38:13.701: D/dbDir created:(15363): false
01-09 21:38:13.701: D/themesDirectroyExist(15363): false
01-09 21:38:13.701: D/themesDir created:(15363): false

我读过类似的问题，但是没有什么有用的。我应该怎么做才能使代码运行？我怎么了

最佳答案

编辑

试试这个:

File mydir = new File(Environment.getExternalStorageDirectory() + "/mydir/");
if(!mydir.exists())
    mydir.mkdirs();
else
    Log.d("error", "dir. already exists");

并重新检查权限

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