手动通知扫描SD卡主动生成缩略图

最近做项目遇到的难题，调用系统拍照获取不到缩略图，非得关机重启才会生成，所以我们要主动通知系统扫描SD卡生成缩略图，

在Android4.4之前也就是以发送一个Action为“Intent.ACTION_MEDIA_MOUNTED”的广播通知执行扫描。如下：

this.sendBroadcast(new Intent(Intent.ACTION_MEDIA_MOUNTED, Uri.parse("file://" + Environment.getExternalStorageDirectory())));

但在Android4.4中，则会抛出以下异常：

W/ActivityManager(  498): Permission Denial: not allowed to send broadcast android.intent.action.MEDIA_MOUNTED from pid=2269, uid=20016 
那是因为Android4.4中限制了系统应用才有权限使用广播通知系统扫描SD卡。 
解决方式： 
使用MediaScannerConnection执行具体文件或文件夹进行扫描。

Intent mediaScanIntent = new Intent(
                    Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
            String path = "file://"
                            + out.getPath();
            Uri contentUri = Uri.parse(path); //out is your output file
            mediaScanIntent.setData(contentUri);
            this.sendBroadcast(mediaScanIntent);

MediaScannerReceiver 源码中的广播接收的部分代码：

 @Override  
    public void onReceive(Context context, Intent intent) {  
        String action = intent.getAction();  
        Uri uri = intent.getData();  
        String externalStoragePath = Environment.getExternalStorageDirectory().getPath();  
  
        if (action.equals(Intent.ACTION_BOOT_COMPLETED)) {  
            // scan internal storage  
            scan(context, MediaProvider.INTERNAL_VOLUME);  
        } else {  
            if (uri.getScheme().equals("file")) {  
                // handle intents related to external storage  
                String path = uri.getPath();  
                if (action.equals(Intent.ACTION_MEDIA_MOUNTED) &&   
                        externalStoragePath.equals(path)) {  
                    scan(context, MediaProvider.EXTERNAL_VOLUME);  
                } else if (action.equals(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE) &&  
                        path != null && path.startsWith(externalStoragePath + "/")) {  
                    scanFile(context, path);  
                }  
            }  
        }  
    }  

所以最后的代码是：

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
            Intent mediaScanIntent = new Intent(
                    Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
            String path = "file://"
                            + out.getPath();
            Uri contentUri = Uri.parse(path); //out is your output file
            mediaScanIntent.setData(contentUri);
            this.sendBroadcast(mediaScanIntent);10         } else {
            sendBroadcast(new Intent(
                    Intent.ACTION_MEDIA_MOUNTED,
                    Uri.parse("file://"
                            + Environment.getExternalStorageDirectory())));
        }