java - 从多个线程修改 ArrayAdapter 时如何防止 ConcurrentModificationException？

Question

我有一个包含文件列表的 RecyclerView。用户可以点击多个 RecyclerView 行，然后上传所选文件。上传文件后(在后台线程上)，我想从 RecyclerView 中删除该行。

但是，我收到错误:

java.util.ConcurrentModificationException
    at java.util.ArrayList$Itr.next(ArrayList.java:860)
    at UploadActivity$11$1.onFinish(UploadActivity.java:471)
    at FileUploader.upload(FileUploader.java:115)
    at UploadActivity$11.run(UploadActivity.java:458)

我知道我有多个线程同时访问和修改我的 RecyclerView 适配器，但我不确定如何解决这个问题(我的代码和尝试在下面发布)。

---

首先我循环遍历选定的 RecyclerView 项目，获取每个选定的文件，然后调用 upload()

// Loop through all selected RecyclerView items 
for (int i = 0; i < selectedIndicies.size(); i++) {

    // Get the i-th selected item
    Upload_Item_Model selectedItem = adapter.getFilteredData().get(selectedIndicies.get(i));

    // Get the file associated with the i-th selected item
    SaveFile file = getFileWithFilename(token, selectedItem.getTitle(), UploadActivity.this);

    // Upload the file
    uploadFile(file);
}

然后我开始一个新线程，开始上传，并定义 onFinish() 回调

public void uploadFile(SaveFile saveFile) {

    ...

    new Thread() {

        @Override
        public void run() {

            // 
            // Uploads the given file, when the upload is complete
            // the onFinish() method is called and the file is passed
            // back so I can update the RecyclerView
            //

            FileUploader.upload(saveFile, new FileUploader.FileUploadListener() {

                @Override
                public void onFinish(SaveFile file) {

                    // Loop through all items in RecyclerView
                    for (Upload_Item_Model item : adapter.getFilteredData()) { // this is line 471 where the crash happens

                        //
                        // If the RecyclerView item has the same name
                        // as the returned file, then it is 
                        // the file I just uploaded
                        //

                        if (item.getTitle().equals(file.getFilename())) {
                            runOnUiThread(() -> {

                                // Removes the item from the adapter
                                adapter.removeItem(item);
                                adapter.notifyDataSetChanged();
                            });

                        }
                    }
                }
            });
        }
    }.start();
}

在适配器中，我有以下访问和修改适配器 ArrayList 的函数。我试图使这些线程安全，但没有成功。

public ArrayList<Upload_Item_Model> getFilteredData() {
    synchronized (this.filteredData) {
        return this.filteredData;
    }
}

public void removeItem(Upload_Item_Model item) {
    synchronized (this.filteredData) {
        this.filteredData.remove(item);
    }
}

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如有任何帮助或建议，我们将不胜感激!

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编辑 + 解决方案

我最终使用 Rajat Mehra 的解决方案使一切正常工作，该解决方案使用单个线程上传所有文件，而不是使用多个线程仅上传一个文件。我确实需要做一些小调整才能让它工作，但现在一切都运行顺利。

public void uploadFile() {

    new Thread() {

        @Override
        public void run() {

            for (int i = 0; i < selectedIndicies.size(); i++) {

                Upload_Item_Model selectedItem = adapter.getFilteredData().get(selectedIndicies.get(i));

                SaveFile file = getFileWithFilename(token, selectedItem.getTitle(), UploadActivity.this);
                FileUploader.upload(file, new FileUploader.FileUploadListener() {

                    @Override
                    public void onFinish() {

                        runOnUiThread(() -> {

                            // I can now simply use the selectedItem here!
                            adapter.removeItem(selectedItem);
                            adapter.notifyDataSetChanged();
                        });
                    }
                });
            }
        }
    }.start();
}

Answer 1

与其创建多个线程，不如创建一个线程并在其中一个接一个地上传所有文件。

public void uploadFile() {


    new Thread() {

        @Override
        public void run() {

            //
            // Uploads the given file, when the upload is complete
            // the onFinish() method is called and the file is passed
            // back so I can update the RecyclerView
            //
            for (int i = 0; i < selectedIndicies.size(); i++) {
                // Get the i-th selected item
                Upload_Item_Model selectedItem = adapter.getFilteredData().get(selectedIndicies.get(i));

                // Get the file associated with the i-th selected item
                SaveFile file = getFileWithFilename(token, selectedItem.getTitle(), UploadActivity.this);
                FileUploader.upload(file, new FileUploader.FileUploadListener() {

                    @Override
                    public void onFinish(SaveFile file) {

                        // Loop through all items in RecyclerView
                        for (Upload_Item_Model item : adapter.getFilteredData()) { // this is line 471 where the crash happens

                            //
                            // If the RecyclerView item has the same name
                            // as the returned file, then it is
                            // the file I just uploaded
                            //

                            if (item.getTitle().equals(file.getFilename())) {
                                runOnUiThread(() -> {

                                    // Removes the item from the adapter
                                    adapter.removeItem(item);
                                    adapter.notifyDataSetChanged();
                                });

                            }
                        }
                    }
                });

            }
        }
    }.start();
}