android - 判断文件夹是否存在，不存在则创建

Question

我注意到在 SO 上对此没有决定性的答案，所以我正在寻找问题“如何检查文件夹是否存在，如果不存在则创建它，使用Google 云端硬盘 Android API？”。理想地展示了使用 ResultCallback 的异步方法和使用 .await() 的同步方法的示例。

附言我知道 this question with the same title ，但公认的答案集中在 isTrashed() 上的已知滞后错误，并且不清楚您在代码中的哪一点真正知道该文件夹存在。其他答案似乎已过时。

Answer 1

This question - 虽然专注于滞后的删除状态问题 - 确实提供了一种用于测试文件夹是否存在的模式。

使用异步回调:

Query query = new Query.Builder()
    .addFilter(Filters.and(Filters.eq(
            SearchableField.TITLE, "MyFolder"),
            Filters.eq(SearchableField.TRASHED, false)))
    .build();
    Drive.DriveApi.query(getGoogleApiClient(), query)
        .setResultCallback(new ResultCallback<DriveApi.MetadataBufferResult>() {
    @Override
    public void onResult(DriveApi.MetadataBufferResult result) {
        if (!result.getStatus().isSuccess()) {
            showMessage("Cannot create folder in the root.");
        } else {
            boolean isFound = false;
            for(Metadata m : result.getMetadataBuffer()) {
                if (m.getTitle().equals("MyFolder")) {
                    showMessage("Folder exists");
                    isFound = true;
                    break;
                }
            }
            if(!isFound) {
                showMessage("Folder not found; creating it.");
                MetadataChangeSet changeSet = new MetadataChangeSet.Builder()
                    .setTitle("MyFolder")
                    .build();
                Drive.DriveApi.getRootFolder(getGoogleApiClient())
                        .createFolder(getGoogleApiClient(), changeSet)
                        .setResultCallback(new ResultCallback<DriveFolder.DriveFolderResult>() {
                    @Override
                    public void onResult(DriveFolder.DriveFolderResult result) {
                        if (!result.getStatus().isSuccess()) {
                            showMessage("Error while trying to create the folder");
                        } else {
                            showMessage("Created a folder");
                        }
                    }
                });
            }
        }
    }
});

使用同步 .await()

Query query = new Query.Builder()
    .addFilter(Filters.and(Filters.eq(
            SearchableField.TITLE, "MyFolder"),
            Filters.eq(SearchableField.TRASHED, false)))
    .build();

    DriveApi.MetadataBufferResult result = Drive.DriveApi.query(getGoogleApiClient(), query)
        .await();

    if (!result.getStatus().isSuccess()) {
        showMessage("Cannot create folder in the root.");
    } else {
        boolean isFound = false;
        for(Metadata m : result.getMetadataBuffer()) {
            if (m.getTitle().equals("MyFolder")) {
                showMessage("Folder exists");
                isFound = true;
                break;
            }
        }
        if(!isFound) {
            showMessage("Folder not found; creating it.");
            MetadataChangeSet changeSet = new MetadataChangeSet.Builder()
                    .setTitle("MyFolder")
                    .build();

            Drive.DriveApi.getRootFolder(getGoogleApiClient())
                        .createFolder(googleApiClient, changeSet).await();

            if (!result.getStatus().isSuccess()) {
                showMessage("Error while trying to create the folder");
            } else {
                showMessage("Created a folder");
            }
        }