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。

1 Intent mediaScanIntent = new Intent(
2                     Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
3             String path = "file://"
4                             + out.getPath();
5             Uri contentUri = Uri.parse(path); //out is your output file
6             mediaScanIntent.setData(contentUri);
7             this.sendBroadcast(mediaScanIntent);


MediaScannerReceiver 源码中的广播接收的部分代码：

 1  @Override  
 2     public void onReceive(Context context, Intent intent) {  
 3         String action = intent.getAction();  
 4         Uri uri = intent.getData();  
 5         String externalStoragePath = Environment.getExternalStorageDirectory().getPath();  
 6   
 7         if (action.equals(Intent.ACTION_BOOT_COMPLETED)) {  
 8             // scan internal storage  
 9             scan(context, MediaProvider.INTERNAL_VOLUME);  
10         } else {  
11             if (uri.getScheme().equals("file")) {  
12                 // handle intents related to external storage  
13                 String path = uri.getPath();  
14                 if (action.equals(Intent.ACTION_MEDIA_MOUNTED) &&   
15                         externalStoragePath.equals(path)) {  
16                     scan(context, MediaProvider.EXTERNAL_VOLUME);  
17                 } else if (action.equals(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE) &&  
18                         path != null && path.startsWith(externalStoragePath + "/")) {  
19                     scanFile(context, path);  
20                 }  
21             }  
22         }  
23     }

所以最后的代码是：

 1 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
 2             Intent mediaScanIntent = new Intent(
 3                     Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
 4             String path = "file://"
 5                             + out.getPath();
 6             Uri contentUri = Uri.parse(path); //out is your output file
 7             mediaScanIntent.setData(contentUri);
 8             this.sendBroadcast(mediaScanIntent);10         } else {
11             sendBroadcast(new Intent(
12                     Intent.ACTION_MEDIA_MOUNTED,
13                     Uri.parse("file://"
14                             + Environment.getExternalStorageDirectory())));
15         }