Android4.4下MediaProvider无法向外置SD卡中文件写数据的解决方法
2019/7/7 20:07:49
本文主要是介绍Android4.4下MediaProvider无法向外置SD卡中文件写数据的解决方法,对大家解决编程问题具有一定的参考价值,需要的程序猿们随着小编来一起学习吧!
本文实例讲述了Android4.4下MediaProvider无法向外置SD卡中文件写数据的解决方法。分享给大家供大家参考,具体如下:
Android4.4平台限制应用对外置SD卡的读写权限。MediaProvider通过 checkAccess方法 限制对外置SD卡的读写。
private void checkAccess(Uri uri, File file, int modeBits) throws FileNotFoundException { final boolean isWrite = (modeBits & MODE_WRITE_ONLY) != 0; final String path; try { path = file.getCanonicalPath(); } catch (IOException e) { throw new IllegalArgumentException("Unable to resolve canonical path for " + file, e); } Context c = getContext(); boolean readGranted = (c.checkCallingOrSelfUriPermission(uri, Intent.FLAG_GRANT_READ_URI_PERMISSION) == PackageManager.PERMISSION_GRANTED); if (path.startsWith(sExternalPath) || path.startsWith(sLegacyPath)) { if (!readGranted) { c.enforceCallingOrSelfPermission( READ_EXTERNAL_STORAGE, "External path: " + path); } if (isWrite) { if (c.checkCallingOrSelfUriPermission(uri, Intent.FLAG_GRANT_WRITE_URI_PERMISSION) != PackageManager.PERMISSION_GRANTED) { c.enforceCallingOrSelfPermission( WRITE_EXTERNAL_STORAGE, "External path: " + path); } } } else if (path.startsWith(sCachePath)) { if (!readGranted) { c.enforceCallingOrSelfPermission( ACCESS_CACHE_FILESYSTEM, "Cache path: " + path); } //外置SD卡,isWrite = true } else if (isWrite) { // don't write to non-cache, non-sdcard files. throw new FileNotFoundException("Can't access " + file); } else if (isSecondaryExternalPath(path)) { // read access is OK with the appropriate permission if (!readGranted) { c.enforceCallingOrSelfPermission( READ_EXTERNAL_STORAGE, "External path: " + path); } } else { checkWorldReadAccess(path); } }
从以上代码我们看出,如果sExternalPath 没有指向外置SD卡并且path 是外置SD卡的文件路径,那么该方法 就会抛出FileNotFoundException,sExternalPath 一般都是指向内部存储
在应用中 我们通常 通过contentresolver.openOutputStream(uri) 来打开存储卡上媒体文件的文件流,如果媒体文件在外置SD卡上,那么我们就无法打开对应的文件流,自然肯定无法向其中写数据。
为了解决该问题,我们只能改变Android4.4平台下Mediaprovider 对向SD卡写数据的限制,具体修改方式如下
private void checkAccess(Uri uri, File file, int modeBits) throws FileNotFoundException { final boolean isWrite = (modeBits & MODE_WRITE_ONLY) != 0; final String path; try { path = file.getCanonicalPath(); } catch (IOException e) { throw new IllegalArgumentException("Unable to resolve canonical path for " + file, e); } Context c = getContext(); boolean readGranted = (c.checkCallingOrSelfUriPermission(uri, Intent.FLAG_GRANT_READ_URI_PERMISSION) == PackageManager.PERMISSION_GRANTED); if (path.startsWith(sExternalPath) || path.startsWith(sLegacyPath) || isSecondaryExternalPath(path)) { if (!readGranted) { c.enforceCallingOrSelfPermission( READ_EXTERNAL_STORAGE, "External path: " + path); } if (isWrite) { if (c.checkCallingOrSelfUriPermission(uri, Intent.FLAG_GRANT_WRITE_URI_PERMISSION) != PackageManager.PERMISSION_GRANTED) { c.enforceCallingOrSelfPermission( WRITE_EXTERNAL_STORAGE, "External path: " + path); } } } else if (path.startsWith(sCachePath)) { if (!readGranted) { c.enforceCallingOrSelfPermission( ACCESS_CACHE_FILESYSTEM, "Cache path: " + path); } //外置SD卡,isWrite = true } else if (isWrite) { // don't write to non-cache, non-sdcard files. throw new FileNotFoundException("Can't access " + file); } else { checkWorldReadAccess(path); } },
对于满足isSecondaryExternalPath(path) 的文件路径,我们都可以进行读写,对于外置SD卡的文件而言 isSecondaryExternalPath(path) 肯定为true
希望本文所述对大家Android程序设计有所帮助。
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