Android存储访问框架的使用小结

存储访问框架，简称：saf， 就是系统文件选择器+文件操作api。先选择文件，在用文件操作api处理文件。系统文件选择器，就和windows的文件选择框一样。

其实绝大多数app,都不会使用这个东西，因为太不方便了。图片，视频，普通文件，需要用户去翻文件夹找，这样的用户体验实在太差了。所以大家都是用第三方的或者自己写一个文件选择器。

之所以讲saf，一，是因为android11以后，使用mediastore无法访问到非多媒体文件了，需要依赖saf了。二，外卡和sd卡的操作依赖于存储访问框架授权。

打开系统文件选择器与文件过滤

 intent intent = new intent(intent.action_open_document);
        intent.addcategory(intent.category_openable);
        intent.settype("application/*");
 
        startactivityforresult(intent, request_code)

settype的值是mime type, 可以是"image/*", "*/*",  其中*是通配符。"image/*"代码所有类型的图片。"*/*"代表所有类型的文件。

当只需要打开几种文件类型时，可以用intent.extra_mime_types。同时settype设成“*/*”。

intent intent = new intent(intent.action_open_document);
        intent.addcategory(intent.category_openable);
        intent.settype("*/*");
        intent.putextra(intent.extra_mime_types, new string[] {
                "application/pdf", // .pdf
                "application/vnd.oasis.opendocument.text", // .odt
                "text/plain" // .txt
        });
 
 
        startactivityforresult(intent, request_code)

intent.action_pick和action_get_content，也可以打开文件选择框。action_get_content更加宽泛，除了文件其他类型的内容还可以取。

 intent intent = new intent(intent.action_pick,  
                    android.provider.mediastore.images.media.external_content_uri);
    intent.settype("image/*");

intent intent = new intent(intent.action_get_content);
        intent.settype("image/*")

下面列举了所有的mime type:

private static final string[][] mime_types = new string[][]{
            {"3gp", "video/3gpp"},
            {"apk", "application/vnd.android.package-archive"},
            {"asf", "video/x-ms-asf"},
            {"avi", "video/x-msvideo"},
            {"bin", "application/octet-stream"},
            {"bmp", "image/bmp"},
            {"c", "text/plain"},
            {"class", "application/octet-stream"},
            {"conf", "text/plain"},
            {"cpp", "text/plain"},
            {"doc", "application/msword"},
            {"docx", "application/vnd.openxmlformats-officedocument.wordprocessingml.document"},
            {"xls", "application/vnd.ms-excel"},
            {"xlsx", "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"},
            {"exe", "application/octet-stream"},
            {"gif", "image/gif"},
            {"gtar", "application/x-gtar"},
            {"gz", "application/x-gzip"},
            {"h", "text/plain"},
            {"htm", "text/html"},
            {"html", "text/html"},
            {"jar", "application/java-archive"},
            {"java", "text/plain"},
            {"jpeg", "image/jpeg"},
            {"jpg", "image/jpeg"},
            {"js", "application/x-javascript"},
            {"log", "text/plain"},
            {"m3u", "audio/x-mpegurl"},
            {"m4a", "audio/mp4a-latm"},
            {"m4b", "audio/mp4a-latm"},
            {"m4p", "audio/mp4a-latm"},
            {"ape", "audio/ape"},
            {"flac", "audio/flac"},
            {"m4u", "video/vnd.mpegurl"},
            {"m4v", "video/x-m4v"},
            {"mov", "video/quicktime"},
            {"mp2", "audio/x-mpeg"},
            {"mp3", "audio/x-mpeg"},
            {"mp4", "video/mp4"},
            {"mkv", "video/x-matroska"},
            {"flv", "video/x-flv"},
            {"divx", "video/x-divx"},
            {"mpa", "video/mpeg"},
            {"mpc", "application/vnd.mpohun.certificate"},
            {"mpe", "video/mpeg"},
            {"mpeg", "video/mpeg"},
            {"mpg", "video/mpeg"},
            {"mpg4", "video/mp4"},
            {"mpga", "audio/mpeg"},
            {"msg", "application/vnd.ms-outlook"},
            {"ogg", "audio/ogg"},
            {"pdf", "application/pdf"},
            {"png", "image/png"},
            {"pps", "application/vnd.ms-powerpoint"},
            {"ppt", "application/vnd.ms-powerpoint"},
            {"pptx", "application/vnd.openxmlformats-officedocument.presentationml.presentation"},
            {"prop", "text/plain"},
            {"rc", "text/plain"},
            {"rmvb", "audio/x-pn-realaudio"},
            {"rtf", "application/rtf"},
            {"sh", "text/plain"},
            {"tar", "application/x-tar"},
            {"tgz", "application/x-compressed"},
            {"txt", "text/plain"},
            {"wav", "audio/x-wav"},
            {"wma", "audio/x-ms-wma"},
            {"wmv", "audio/x-ms-wmv"},
            {"wps", "application/vnd.ms-works"},
            {"xml", "text/plain"},
            {"z", "application/x-compress"},
            {"zip", "application/x-zip-compressed"},
            {"rar", "application/x-rar"},
            {"", "*/*"}
    };

打开指定文件夹

利用documentscontract.extra_initial_uri，在打开文件选择器的时候，跳转到指定文件夹。只有android 8以上才行。

uri uri = uri.parse("content://com.android.externalstorage.documents/document/primary:download");
intent intent = new intent(intent.action_open_document);
intent.addcategory(intent.category_openable);
intent.settype("*/*");
intent.putextra(documentscontract.extra_initial_uri, uri);
startactivityforresult(intent, 1);

文件夹权限申请

当需要读取非公共文件夹里面的文件时，可以申请授权，授权后保存uri，之后可以拼接这个uri操作文件夹里的所有文件。

尤其是sd卡，从android 5 开始文件的修改删除必须先授权，且必须通过svf框架接口才能操作。

可以使用extra_initial_uri，打开指定文件夹，让用户授权

  intent intent = new intent(intent.action_open_document_tree);
       uri uri = uri.parse("content://com.android.externalstorage.documents/document/primary:download");
 
       intent.putextra(documentscontract.extra_initial_uri, uri);
 
        startactivityforresult(intent) 

需要注意的是，android 11以后，无法授权访问存储根目录，以及download/，android/, 这两个文件夹也无法授权。

创建文件夹

创建文件夹有两个情况，一个是在已授权的文件夹下，可以使用svf框架api。

documentscontract.createdocument()

还有一种是在无授权的文件夹下创建，那么可以直接指定类型和名字，通过跳系统选择框创建。

 intent intent = new intent(intent.action_create_document);
        intent.addcategory(intent.category_openable);
        intent.settype("application/txt");
        intent.putextra(intent.extra_title, "testfile.txt");
 
        startactivityforresult(intent)

存储访问框架api

存储访问框架api，都在documentscontract里面，典型的有：

public static @nullable uri renamedocument(@nonnull contentresolver content,
            @nonnull uri documenturi, @nonnull string displayname) throws filenotfoundexception {
 
    }
 
    /**
     * delete the given document.
     *
     * @param documenturi document with {@link document#flag_supports_delete}
     * @return if the document was deleted successfully.
     */
    public static boolean deletedocument(@nonnull contentresolver content, @nonnull uri documenturi)
            throws filenotfoundexception {
 
    }
 
    /**
     * copies the given document.
     *
     * @param sourcedocumenturi document with {@link document#flag_supports_copy}
     * @param targetparentdocumenturi document which will become a parent of the source
     *         document's copy.
     * @return the copied document, or {@code null} if failed.
     */
    public static @nullable uri copydocument(@nonnull contentresolver content,
            @nonnull uri sourcedocumenturi, @nonnull uri targetparentdocumenturi)
            throws filenotfoundexception {
 
    }
 
    /**
     * moves the given document under a new parent.
     *
     * @param sourcedocumenturi document with {@link document#flag_supports_move}
     * @param sourceparentdocumenturi parent document of the document to move.
     * @param targetparentdocumenturi document which will become a new parent of the source
     *         document.
     * @return the moved document, or {@code null} if failed.
     */
    public static @nullable uri movedocument(@nonnull contentresolver content,
            @nonnull uri sourcedocumenturi, @nonnull uri sourceparentdocumenturi,
            @nonnull uri targetparentdocumenturi) throws filenotfoundexception {
 
    }
 
    /**
     * removes the given document from a parent directory.
     *
     * <p>in contrast to {@link #deletedocument} it requires specifying the parent.
     * this method is especially useful if the document can be in multiple parents.
     *
     * @param documenturi document with {@link document#flag_supports_remove}
     * @param parentdocumenturi parent document of the document to remove.
     * @return true if the document was removed successfully.
     */
    public static boolean removedocument(@nonnull contentresolver content, @nonnull uri documenturi,
            @nonnull uri parentdocumenturi) throws filenotfoundexception {
 
    }

获取文件夹文件

使用documentfile类获取文件夹里文件列表。

private activityresultlauncher<object> openfile() {
        intent intent = new intent(intent.action_open_document_tree);
        uri uri = uri.parse("content://com.android.externalstorage.documents/document/primary:authsdk");
        intent.putextra(documentscontract.extra_initial_uri, uri);
        return startactivityforresult(intent, new activityresultcallback<intent>() {
            @override
            public void onactivityresult(intent result) {
 
                for (documentfile documentfile : documentfile.fromtreeuri(baseapplication.getinstance().getapplicationcontext(), uri.parse(result.getdata().tostring())).listfiles()) {
 
                     log.i("", documentfile.geturi());
                }
            }
        });
    }

下面的代码演示了，使用svf读取文件内容，写内容，通过mediastore查询文件属性。

private activityresultlauncher<object> openfile() {
        intent intent = new intent(intent.action_open_document_tree);
        uri uri = uri.parse("content://com.android.externalstorage.documents/document/primary:authsdk");
        intent.putextra(documentscontract.extra_initial_uri, uri);
 
        return startactivityforresult(intent, new activityresultcallback<intent>() {
            @override
            public void onactivityresult(intent result) {
 
                for (documentfile documentfile : documentfile.fromtreeuri(baseapplication.getinstance().getapplicationcontext(), uri.parse(result.getdata().tostring())).listfiles()) {
                    try {
                        inputstream inputstream = baseapplication.getinstance().getcontentresolver().openinputstream(documentfile.geturi());
                        byte[] readdata = new byte[1024];
                        inputstream.read(readdata);
 
                        outputstream outputstream = baseapplication.getinstance().getcontentresolver().openoutputstream(documentfile.geturi());
                        byte[] writedata = "alan gong".getbytes(standardcharsets.utf_8);
                        outputstream.write(writedata, 0, 9);
                        outputstream.close();
                        if (build.version.sdk_int >= build.version_codes.q) {
                            uri mediauri = mediastore.getmediauri(baseapplication.getinstance().getapplicationcontext(), documentfile.geturi());
                            long fileid = contenturis.parseid(mediauri);
                            cursor query = baseapplication.getinstance().getcontentresolver().query(documentfile.geturi(), null, mediastore.mediacolumns._id + "=" + fileid, null, null);
                            int columnindex = query.getcolumnindexorthrow(mediastore.mediacolumns.mime_type);
                            string mimetype = query.getstring(columnindex);
                            log.i("", "");
                        }
 
                    } catch (filenotfoundexception e) {
                        e.printstacktrace();
                    } catch (ioexception e) {
                        e.printstacktrace();
                    }
                }
            }
        });
    }

使用mediastore.getmediauri(documenturi)可以转换，mediastore uri 和 document uri。通过mediastore uri中的数据库id，就可以查询文件的所有属性了。

mediastore uri：content://media/external_primary/file/101750

document uri: content://com.android.externalstorage.documents/tree/primary%3aauthsdk

另外，

非公共目录下不能用file api操作的，即使通过svf授权了， read_extrnal_permission的权限也给了。还是会抛出filenotfoundexception， 并且显示permission deny。

和mediastore api的不同

存储访问框架api和mediastore api的差异，在于存储访问框架api，是基于系统文件选择框的，用户选择了文件，那么相当于授权了， 可以访问所有类型的文件。而mediastore的特点是可以查询出所有文件，但是开启分区存储后，只能查处多媒体文件，其他类型文件是不可以的。

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