Android 存储用例和最佳做法

为了让用户更好地控制自己的文件并减少混乱，Android 10 针对应用推出了一种新的存储范例，称为分区存储。

分区存储改变了应用在设备的外部存储设备中存储和访问文件的方式。为了帮助您迁移应用以支持分区存储，请遵循本指南中有关常见存储用例的最佳做法。

这些用例分为两类：处理媒体文件和处理非媒体文件。

访问共享存储空间中的媒体文件

• 照片选择器

照片选择器适用于符合以下条件的设备：

• 搭载 Android 11（API 级别 30）或更高版本
• 通过 Google 系统更新接收对模块化系统组件的更改

检查照片选择器是否可用

import android.os.ext.SdkExtensions.getExtensionVersion;

private boolean isPhotoPickerAvailable() {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
        return true;
    } else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
        return getExtensionVersion(Build.VERSION_CODES.R) >= 2;
    } else
        return false;
    }
}

public void launchPhotoPicker() {
    if (isPhotoPickerAvailable()) {
        // To launch the system photo picker, invoke an intent that includes the
        // ACTION_PICK_IMAGES action. Consider adding support for the
        // EXTRA_PICK_IMAGES_MAX intent extra.
    } else {
        // Consider implementing fallback functionality so that users can still
        // select images and videos.
    }
}

单文件选择

// Registers a photo picker activity launcher in single-select mode.
ActivityResultLauncher<PickVisualMediaRequest> pickMedia =
        registerForActivityResult(new PickVisualMedia(), uri -> {
    // Callback is invoked after the user selects a media item or closes the
    // photo picker.
    if (uri != null) {
        Log.d("PhotoPicker", "Selected URI: " + uri);
    } else {
        Log.d("PhotoPicker", "No media selected");
    }
});

// Include only one of the following calls to launch(), depending on the types
// of media that you want to allow the user to choose from.

// Launch the photo picker and allow the user to choose images and videos.
pickMedia.launch(new PickVisualMediaRequest.Builder()
        .setMediaType(PickVisualMedia.ImageAndVideo.INSTANCE)
        .build());

// Launch the photo picker and allow the user to choose only images.
pickMedia.launch(new PickVisualMediaRequest.Builder()
        .setMediaType(PickVisualMedia.ImageOnly.INSTANCE)
        .build());

// Launch the photo picker and allow the user to choose only videos.
pickMedia.launch(new PickVisualMediaRequest.Builder()
        .setMediaType(PickVisualMedia.VideoOnly.INSTANCE)
        .build());

// Launch the photo picker and allow the user to choose only images/videos of a
// specific MIME type, such as GIFs.
String mimeType = "image/gif";
pickMedia.launch(new PickVisualMediaRequest.Builder()
        .setMediaType(new PickVisualMedia.SingleMimeType(mimeType))
        .build());

多文件选择

// Registering Photo Picker activity launcher with multiple selects (5 max in this example)
ActivityResultLauncher<PickVisualMediaRequest> pickMultipleMedia =
        registerForActivityResult(new PickMultipleVisualMedia(5), uris -> {
    // Callback is invoked after the user selects media items or closes the
    // photo picker.
    if (!uris.isEmpty()) {
        Log.d("PhotoPicker", "Number of items selected: " + uris.size());
    } else {
        Log.d("PhotoPicker", "No media selected");
    }
});

// For this example, launch the photo picker and allow the user to choose images
// and videos. If you want the user to select a specific type of media file,
// use the overloaded versions of launch(), as shown in the section about how
// to select a single media item.
pickMultipleMedia.launch(new PickVisualMediaRequest.Builder()
        .setMediaType(PickVisualMedia.ImageAndVideo.INSTANCE)
        .build());

使用ContentResolver查询媒体文件

1. 自己创建的文件: 无需权限

2. 非自己创建文件: sdk 28 及之前需要android.permission.READ_EXTERNAL_STORAGE、android.permission.WRITE_EXTERNAL_STORAGE

sdk 28之后使用 android.permission.READ_MEDIA_IMAGES 、android.permission.READ_MEDIA_VIDEO 、android.permission.READ_MEDIA_AUDIO权限

// Need the READ_EXTERNAL_STORAGE permission if accessing video files that your
// app didn't create.

// Container for information about each video.
class Video {
    private final Uri uri;
    private final String name;
    private final int duration;
    private final int size;

    public Video(Uri uri, String name, int duration, int size) {
        this.uri = uri;
        this.name = name;
        this.duration = duration;
        this.size = size;
    }
}
List<Video> videoList = new ArrayList<Video>();

Uri collection;
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
    collection = MediaStore.Video.Media.getContentUri(MediaStore.VOLUME_EXTERNAL);
} else {
    collection = MediaStore.Video.Media.EXTERNAL_CONTENT_URI;
}

String[] projection = new String[] {
    MediaStore.Video.Media._ID,
    MediaStore.Video.Media.DISPLAY_NAME,
    MediaStore.Video.Media.DURATION,
    MediaStore.Video.Media.SIZE
};
String selection = MediaStore.Video.Media.DURATION +
        " >= ?";
String[] selectionArgs = new String[] {
    String.valueOf(TimeUnit.MILLISECONDS.convert(5, TimeUnit.MINUTES));
};
String sortOrder = MediaStore.Video.Media.DISPLAY_NAME + " ASC";

try (Cursor cursor = getApplicationContext().getContentResolver().query(
    collection,
    projection,
    selection,
    selectionArgs,
    sortOrder
)) {
    // Cache column indices.
    int idColumn = cursor.getColumnIndexOrThrow(MediaStore.Video.Media._ID);
    int nameColumn =
            cursor.getColumnIndexOrThrow(MediaStore.Video.Media.DISPLAY_NAME);
    int durationColumn =
            cursor.getColumnIndexOrThrow(MediaStore.Video.Media.DURATION);
    int sizeColumn = cursor.getColumnIndexOrThrow(MediaStore.Video.Media.SIZE);

    while (cursor.moveToNext()) {
        // Get values of columns for a given video.
        long id = cursor.getLong(idColumn);
        String name = cursor.getString(nameColumn);
        int duration = cursor.getInt(durationColumn);
        int size = cursor.getInt(sizeColumn);

        Uri contentUri = ContentUris.withAppendedId(
                MediaStore.Video.Media.EXTERNAL_CONTENT_URI, id);

        // Stores column values and the contentUri in a local object
        // that represents the media file.
        videoList.add(new Video(contentUri, name, duration, size));
    }
}

非媒体文件

使用文件选择器

无需任何权限, 用户选择后默许对该文件有权操作

// 创建文件
Intent(Intent.ACTION_CREATE_DOCUMENT).apply {
    addCategory(Intent.CATEGORY_OPENABLE)
    type = "application/pdf"
    putExtra(Intent.EXTRA_TITLE, "invoice.pdf")

    // Optionally, specify a URI for the directory that should be opened in
    // the system file picker before your app creates the document.
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        putExtra(DocumentsContract.EXTRA_INITIAL_URI, input)
    }
}

// 打开文件
Intent(Intent.ACTION_OPEN_DOCUMENT).apply {
    addCategory(Intent.CATEGORY_OPENABLE)
    type = "application/pdf"

    // Optionally, specify a URI for the file that should appear in the
    // system file picker when it loads.
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        putExtra(DocumentsContract.EXTRA_INITIAL_URI, input)
    }
}

// 授权文件夹权限
Intent(Intent.ACTION_OPEN_DOCUMENT_TREE).apply {
    // Optionally, specify a URI for the directory that should be opened in
    // the system file picker when it loads.
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        putExtra(DocumentsContract.EXTRA_INITIAL_URI, input)
    }
}

共享文件

指定 FileProvider

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.myapp">
    <application
        ...>
        <provider
            android:name="androidx.core.content.FileProvider"
            android:authorities="com.example.myapp.fileprovider"
            android:grantUriPermissions="true"
            android:exported="false">
            <meta-data
                android:name="android.support.FILE_PROVIDER_PATHS"
                android:resource="@xml/filepaths" />
        </provider>
        ...
    </application>
</manifest>

指定可共享的目录

<paths>
    <files-path path="images/" name="myimages" />
</paths>

注意：您只能通过 XML 文件指定要共享的目录，无法以编程方式添加目录。

参考

1. Android Q 存储新特性适配脑壳疼？指南来了！
2. Android 存储用例和最佳做法
3. 数据和文件存储概览
4. 创建自定义文档提供程序
5. 从共享存储空间访问文档和其他文件
6. 照片选择器