Android 中 Environment.getExternalStorageDirectory()无效

　　我们在处理缓存的时候，并不是每次都会在应用私有存储空间那里保存，很多时候是需要用到ExternalStorage。我们平时一般都是用Environment.getExternalStorageDirectory()，这在6.0以前一直是好的，（即使不对，那你的问题应该是没注意加权限，或者是格式不对之类又或者sdcard被移走了等等）。但是到了6.0以后，就发现怎么都不无法创建文件了。很多人就疑惑，该加的权限都加了，怎么就没法创建呢？

　　原因是Android 6.0以后，google升级了Android的权限管理机制，对于一些敏感的权限，需要显性申请并被用户允许才可能运行。

    private void checkPermission() {

        if (Build.VERSION.SDK_INT >= 23) {
            int write = checkSelfPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE);
            int read = checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE);
            if (write != PackageManager.PERMISSION_GRANTED || read != PackageManager.PERMISSION_GRANTED) {
                requestPermissions(new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE, Manifest.permission.READ_EXTERNAL_STORAGE}, 300);
            } else {
                String name = "CrashDirectory";
                File file1 = new File(Environment.getExternalStorageDirectory(), name);
                if (file1.mkdirs()) {
                    Log.i("wytings", "permission -------------> " + file1.getAbsolutePath());
                } else {
                    Log.i("wytings", "permission -------------fail to make file ");
                }
            }
        } else {
            Log.i("wytings", "------------- Build.VERSION.SDK_INT < 23 ------------");
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        if (requestCode == 300) {
            Log.i("wytings", "--------------requestCode == 300->" + requestCode + "," + permissions.length + "," + grantResults.length);
        } else {
            Log.i("wytings", "--------------requestCode != 300->" + requestCode + "," + permissions + "," + grantResults);
        }
    }

备注：附上android的权限组，因为同一组的任何一个权限被授权了，其他权限也自动被授权。例如，一旦WRITE_EXTERNAL_STORAGE被授权了，app也有READ_EXTERNAL_STORAGE.所以，你只申请一个就可以了。