Android9.0中应用如何通过SAF框架写入外置SD卡

背景介绍 Overview

基于SAF框架写入外置SD卡网上相关资料比较少，现整理一下具体实现方法，如果是访问主存储，弹出授权后即可正常写入，如果是副卡，在Android9.0上必须要使用SAF框架。
本文档详细介绍了应用如何使用Storage Access Framework （SAF框架）访问External SDcard的方法，使得第三方APP或者应用开发者快速集成写入sd卡方法。本文将采用Android原生ScreenShot截图功能集成SAF框架为例，介绍如何打造可以写入外部SD卡方法

申请权限

首先申请写入外部SD卡的权限需要在Activity中，由于Screenshot中无Activity，因此需要创建一个透明Activity来获取Activity的上下文Context

<activity android:name=".screenshot.ScreenshotPermissionsActivity"android:theme="@android:style/Theme.Translucent.NoTitleBar"android:finishOnCloseSystemDialogs="true"android:excludeFromRecents="true"><intent-filter><action android:name="com.android.intent.action.REQUEST_SCREENSHOT_STORAGE_PERMISSION" /></intent-filter>
</activity>

在需要写入T卡的位置先判断是否有写入SD卡权限，如果没有，则启动权限申请的ScreenshotPermissionsActivity

String rootPath  = WriteSDFileUtil.getRootPath(mContext);
if (SaveImageInBackgroundTask.SAVE_SPRD_EXTERNAL_STORAGE && !TextUtils.isEmpty(rootPath)) {if (WriteSDFileUtil.hasWriteSDPermission(mContext)) {saveScreenshot2SD(mScreenBitmap);} else {WriteSDFileUtil.startPermissionActivity(mContext);permissonHandler.sendEmptyMessageDelayed(CHECK_PERMISSION, CHECK_DURATION);}
}

getRootPath方法如下：

public static String getRootPath(Context context) {String rootPath = null;StorageManager storageManager = (StorageManager) context.getSystemService(Context.STORAGE_SERVICE);List<StorageVolume> volumes = storageManager.getStorageVolumes();for (StorageVolume volume : volumes) {File volumePath = volume.getPathFile();if (!volume.isPrimary() && volumePath != null &&Environment.getExternalStorageState(volumePath).equals(Environment.MEDIA_MOUNTED)&& !volumePath.toString().contains(STORAGE_PATH_EMULATED)) {rootPath = volumePath.toString();}}Log.i(TAG, "getRootPath rootPath: " + rootPath);return rootPath;
}

hasWriteSDPermission方法如下：

public static boolean hasWriteSDPermission(Context context) {return StorageUtil.getInstance().getCurrentAccessUri(context.getContentResolver()) != null;
}

通过getCurrentAccessUri来判断是否有写SD卡的权限，如果getCurrentAccessUri获取的URI为null则无写入SD卡的权限：

public Uri getCurrentAccessUri(ContentResolver contentResolver) {List<UriPermission> uriPermissions = contentResolver.getPersistedUriPermissions();Log.i(TAG, "getCurrentAccessUri exactStorageName ");for (UriPermission permission : uriPermissions) {Log.i(TAG, "getCurrentAccessUri permission: " + permission.toString());return permission.getUri();}Log.i(TAG, "getCurrentAccessUri return null");return null;
}

ScreenshotPermissionsActivity中权限申请代码：

// for external storage access permission
private void requestScopedDirectoryAccess() {int requestCode = -1;StorageManager storageManager = (StorageManager) getSystemService(Context.STORAGE_SERVICE);List<StorageVolume> volumes = storageManager.getStorageVolumes();Log.i(TAG, "requestScopedDirectoryAccess storagePath: " + WriteSDFileUtil.STORAGE_PATH_EMULATED);for (StorageVolume volume : volumes) {File volumePath = volume.getPathFile();Log.i(TAG, "requestScopedDirectoryAccess volumePath: " + volumePath);if (!volume.isPrimary() && volumePath != null &&Environment.getExternalStorageState(volumePath).equals(Environment.MEDIA_MOUNTED)&& !volumePath.toString().contains(WriteSDFileUtil.STORAGE_PATH_EMULATED)) {mRootPath = volumePath.toString();Log.i(TAG, "really createAccessIntent for mRootPath: " + mRootPath);final Intent intent = volume.createAccessIntent(null);Log.i(TAG, "really createAccessIntent for intent: " + intent);if (intent != null) {intent.putExtra(Intent.EXTRA_PACKAGE_NAME, "com.android.systemui");intent.putExtra("screenshot", true);startActivityForResult(intent, SCOPED_REQUEST_CODE);Log.i(TAG, "really createAccessIntent for intent: " + intent.getStringExtra(Intent.EXTRA_PACKAGE_NAME));}}}
}

申请后会弹出权限框
此时如果用户点击授权按钮，则会回调ScreenshotPermissionsActivity中的onActivityResult方法：

public void onActivityResult(int requestCode, int resultCode, Intent data) {Log.d(TAG, " requestCode = " + requestCode + " resultCode = " + resultCode+ " data = " + data);if (requestCode == SCOPED_REQUEST_CODE) {if (resultCode == Activity.RESULT_CANCELED) {Log.d("huasong", "RESULT_CANCELED:");sendBroadcastAsUser(new Intent("action.screenshot.permissin.deny"), UserHandle.ALL);ScreenshotPermissionsActivity.this.finish();} else if (resultCode == Activity.RESULT_OK) {Log.d(TAG, "yeah!!!!");Uri uri = data != null ? data.getData() : null;final int takeFlags = data.getFlags() & (Intent.FLAG_GRANT_READ_URI_PERMISSION| Intent.FLAG_GRANT_WRITE_URI_PERMISSION);getContentResolver().takePersistableUriPermission(uri, takeFlags);ScreenshotPermissionsActivity.this.finish();}}
}

在获取RESULT_OK用户授权后，需要调用takePersistableUriPermission保存权限uri，否则下次需要重新授权

写入文件

主要采用WriteSDFileUtil的WriteSDFile方法首先传入RootPath

String picName = String.format(SaveImageInBackgroundTask.SCREENSHOT_FILE_NAME_TEMPLATE,new SimpleDateFormat("yyyyMMdd-HHmmss").format(new Date(System.currentTimeMillis())));
String rootPath  = WriteSDFileUtil.getRootPath(mContext);
WriteSDFileUtil.WriteSDFile(mContext, bitmap, rootPath, picName);

WriteSDFile方法：

public static void WriteSDFile(Context context, Bitmap bitmap, String rootPath, String saveName) {Uri root = StorageUtil.getInstance().getCurrentAccessUri(context.getContentResolver());Uri folder = root;try {String pictureDir = rootPath + File.separator + PICTURE_DIR;String screenshotDir = pictureDir + File.separator + SCREENSHOT_DIR;String saveFileName = screenshotDir + File.separator + saveName;if (new File(pictureDir).exists()) {folder = SafTools.getDocumentFileByPath(context, root, pictureDir).getUri();} else {folder = DocumentsContract.createDocument(context.getContentResolver(), root,DocumentsContract.Document.MIME_TYPE_DIR, PICTURE_DIR);}if (new File(screenshotDir).exists()) {folder = SafTools.getDocumentFileByPath(context, folder, screenshotDir).getUri();} else {folder = DocumentsContract.createDocument(context.getContentResolver(), folder,DocumentsContract.Document.MIME_TYPE_DIR, SCREENSHOT_DIR);}Uri file = SafTools.createDocument(context.getContentResolver(), folder, new File(saveFileName), MIME_IMAGE);try {ParcelFileDescriptor pfd = context.getContentResolver().openFileDescriptor(file, "w");FileOutputStream fileOutputStream = new FileOutputStream(pfd.getFileDescriptor());fileOutputStream.write(getBytesByBitmaps(bitmap));fileOutputStream.close();pfd.close();} catch (Exception e) {Log.d(TAG, "exception:", e);}} catch (Exception e) {}
}

SAFTools中createDocument方法：

/**
* Use tarParUri to create this target file. If need to create lots of documents, not suggest.
* @param resolver
* @param tarParUri
* @param target
* @param mimeType
* @return
*/
public static Uri createDocument(ContentResolver resolver, Uri tarParUri,  File target, String mimeType){Uri result = null;if(tarParUri != null){try{result = DocumentsContract.createDocument(resolver, tarParUri, mimeType, target.getName());} catch (Exception e) {result = null;Log.e(TAG, "createDocument failed! Exception:"+ e);}}if(result == null){Log.d(TAG,"createDocument failed!");}return result;
}

修改DocumentUI代码

由于权限框拒绝后，下次需要重新弹出，且不可被用户选择“拒绝后不再提示”功能，需要修改DocumentUI弹出框的“不再提示”功能不可见，修改方式如下：
packages\apps\DocumentsUI\com\android\documentsui\ScopedAccessActivity.java

private static boolean mIsForScreenshot;
mIsForScreenshot = intent.getBooleanExtra("screenshot", false);
Log.d(TAG, "isForScreenshot:" + mIsForScreenshot);
if (getScopedAccessPermissionStatus(context, mActivity.getCallingPackage(),mVolumeUuid, directoryName) == PERMISSION_ASK_AGAIN) {mDontAskAgain.setVisibility(View.VISIBLE);mDontAskAgain.setOnCheckedChangeListener(new OnCheckedChangeListener() {@Overridepublic void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {mDialog.getButton(DialogInterface.BUTTON_POSITIVE).setEnabled(!isChecked);}});
}
if (mIsForScreenshot) {mDontAskAgain.setVisibility(View.GONE);mDialog.setCanceledOnTouchOutside(false);
}