创建文件后，ContentResolver在立即查询中不包含刚刚创建的图像 [英] ContentResolver doesn't contain just created image in an immediate query after creation of file

问题描述

我正在使用此代码使用documentFile.createFile()

I'm using this code to copy an image using documentFile.createFile()

private void newcopyFile(File fileInput, String outputParentPath,
                            String mimeType, String newFileName) {

        DocumentFile documentFileGoal = DocumentFile.fromTreeUri(this, treeUri);

        String[] parts = outputParentPath.split("\\/");
        for (int i = 3; i < parts.length; i++) {
            if (documentFileGoal != null) {
                documentFileGoal = documentFileGoal.findFile(parts[i]);
            }
        }
        if (documentFileGoal == null) {
            Toast.makeText(MainActivity.this, "Directory not found", Toast.LENGTH_SHORT).show();
            return;
        }

        DocumentFile documentFileNewFile = documentFileGoal.createFile(mimeType, newFileName);

        InputStream inputStream = null;
        OutputStream outputStream = null;
        try {
            outputStream = getContentResolver().openOutputStream(documentFileNewFile.getUri());
            inputStream = new FileInputStream(fileInput);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        try {
            if (outputStream != null) {
                byte[] buffer = new byte[1024];
                int read;
                if (inputStream != null) {
                    while ((read = inputStream.read(buffer)) != -1) {
                        outputStream.write(buffer, 0, read);
                    }
                }
                if (inputStream != null) {
                    inputStream.close();
                }
                inputStream = null;
                outputStream.flush();
                outputStream.close();
                outputStream = null;
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

这是我在创建图像后查询ContentResolver的方式，以立即刷新我的图像库，其中包含应该包含新创建图像信息的查询结果.

And this is how I query ContentResolver after creating image, to immediately refresh my image gallery with the result of query which should contain info of newly created image.

cursorPhotos = MainActivity.this.getContentResolver().query(MediaStore.Images.Media.EXTERNAL_CONTENT_URI,
                    projectionsImages,
                    null,
                    null,
                    MediaStore.Images.Media.DATE_TAKEN + " DESC"
            );

但是立即查询找不到新创建的图像. 如果过一会儿再次运行查询，结果中将出现新创建的图像.

But immediate query couldn't find newly created image. And if I run query again after a moment, newly created image is there in the result.

为新创建的图像提供信息似乎需要花费ContentResolver的时间(如果由ContentResolver负责)，因为在我运行即时查询时它将在后台运行.

It seems providing information for newly created image takes time for ContentResolver(if ContentResolver is in charge for it) as it would be running in background while I run immediate query.

是否有任何方法或侦听器知道ContentResolver何时注册了新创建的图像?

Is there any method or listener to know when the newly created image is registered by ContentResolver?

推荐答案

您可以使用这或这就是我对ContentResolver更改实施侦听器(观察者)的方法，使用ContentObserver知道什么时候才是运行查询以从中获取新创建的图像的适当时间ContentResolver.

You could use this or this is how I've implemented a listener(observer) to ContentResolver changes, using ContentObserver to know when is the appropriate time to run a query for getting newly created image from ContentResolver.

首先创建ContentObserver类:

此类的名称告诉我们，它会在我们所需的Uri中观察任何内容更改.

This class as its name tells us, observes any content changes in our desired Uri.

class MyObserver extends ContentObserver {
    public MyObserver(android.os.Handler handler) {
        super(handler);
    }

    @Override
    public void onChange(boolean selfChange) {
        this.onChange(selfChange, null);
    }

    @Override
    public void onChange(boolean selfChange, Uri uri) {
        //(SDK>=16)
        // do s.th.
        // depending on the handler you might be on the UI
        // thread, so be cautious!

        // This is my AsyncTask that queries ContentResolver which now
        // is aware of newly created media file.
        // You implement your own query here in whatever way you like
        // This query will contain info for newly created image
        asyncTaskGetPhotosVideos = new AsyncTaskGetPhotosVideos();
        asyncTaskGetPhotosVideos.execute();
    }
}

，在复制方法的最后，您可以在特定的Uri上将ContentObserver设置为ContentResolver.

and at the end of your copy method, you could set ContentObserver to your ContentResolver on specific Uri.

 getContentResolver().registerContentObserver(
         MediaStore.Images.Media.EXTERNAL_CONTENT_URI,
         true,
         myObserver);

并且不要忘记注销观察者的注册，否则您将面临内存泄漏.我希望在AsyncTask(onPostExecute)的末尾执行该操作.

and don't forget to unregister your observer otherwise you will face memory leak. I would prefer to do it at the end of my AsyncTask (onPostExecute).

getContentResolver().unregisterContentObserver(myObserver);

您可以选择在整个应用程序生命周期中的所需Uri上放置ContentObserver，以便在从应用程序外部或内部更改，删除或插入媒体时得到通知.

You could choose to have a ContentObserver on your desired Uri through your entire app lifecycle to get notified whenever a media got changed, deleted or inserted from outside or within your app.

对于这种方法，您可以在onResume()生命周期方法中注册观察者，而在onPause()方法中注销它.

For this approach, you could register your observer in the onResume() lifecycle method and unregister it in the onPause() method.

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