关于Android的存储

关于数据的存储

https://medium.com/@sandeepkella23/exploring-data-storage-in-android-types-advantages-datastore-real-time-use-cases-and-best-8bb42fa6792e

sp,datastore,内部存储，外部存储，数据库等对比，大概的一些概念

关于内部存储和外部存储的一些区别，以及API29与API30平台上的区别PL这个视频大概有说到

https://www.youtube.com/watch?v=TkOzcyzH1hU&list=PLQkwcJG4YTCR9jZq8O19nUL2hLqmLYX4M

内部存储只有自己的应用可以访问，而且应用卸载后，可一起删除

外部存储的的话，有个问题，就是应用卸载之后，文件还遗留着，然后Android就出了storage scope来解决这个问题，但是这个在Android 10之后引入的storagescope，但是在Andorid 11之后才强制；

内部存储

读取内部文件

   private suspend fun loadPhotosFromInternalStorage(): List<InternalStoragePhoto> {
        return withContext(Dispatchers.IO) {
            val files = filesDir.listFiles()
            files?.filter { it.canRead() && it.isFile && it.name.endsWith(".jpg") }?.map {
                val bytes = it.readBytes()
                val bmp = BitmapFactory.decodeByteArray(bytes, 0, bytes.size)
                InternalStoragePhoto(it.name, bmp)
            } ?: listOf()
        }
    }

写入内部文件

 private suspend fun savePhotoToInternalStorage(filename: String, bmp: Bitmap): Boolean {
        return withContext(Dispatchers.IO) {
            try {
                openFileOutput("$filename.jpg", MODE_PRIVATE).use { stream ->
                    if(!bmp.compress(Bitmap.CompressFormat.JPEG, 95, stream)) {
                        throw IOException("Couldn't save bitmap.")
                    }
                }
                true
            } catch(e: IOException) {
                e.printStackTrace()
                false
            }
        }
    }

删除内部文件

 private suspend fun deletePhotoFromInternalStorage(filename: String): Boolean {
        return withContext(Dispatchers.IO) {
            try {
                deleteFile(filename) //context就有的方法
            } catch (e: Exception) {
                e.printStackTrace()
                false
            }
        }
    }

外部存储

读取外部文件

首先要有权限READ_EXTERNAL_STORAGE

//通过contentprovider来查询外部共享媒体文件
    private suspend fun loadPhotosFromExternalStorage(): List<SharedStoragePhoto> {
        return withContext(Dispatchers.IO) {
            val collection = sdk29AndUp { //api29以上
                MediaStore.Images.Media.getContentUri(MediaStore.VOLUME_EXTERNAL)
            } ?: MediaStore.Images.Media.EXTERNAL_CONTENT_URI

            val projection = arrayOf(
                MediaStore.Images.Media._ID,
                MediaStore.Images.Media.DISPLAY_NAME,
                MediaStore.Images.Media.WIDTH,
                MediaStore.Images.Media.HEIGHT,
            )
            val photos = mutableListOf<SharedStoragePhoto>()
            contentResolver.query(
                collection,
                projection,
                null,
                null,
                "${MediaStore.Images.Media.DISPLAY_NAME} ASC"
            )?.use { cursor ->
                val idColumn = cursor.getColumnIndexOrThrow(MediaStore.Images.Media._ID)
                val displayNameColumn = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DISPLAY_NAME)
                val widthColumn = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.WIDTH)
                val heightColumn = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.HEIGHT)

                while(cursor.moveToNext()) {
                    val id = cursor.getLong(idColumn)
                    val displayName = cursor.getString(displayNameColumn)
                    val width = cursor.getInt(widthColumn)
                    val height = cursor.getInt(heightColumn)
                    val contentUri = ContentUris.withAppendedId(
                        MediaStore.Images.Media.EXTERNAL_CONTENT_URI,
                        id
                    )
                    photos.add(SharedStoragePhoto(id, displayName, width, height, contentUri))
                }
                photos.toList()
            } ?: listOf()
        }
    }

写入外部文件

权限WRITE_EXTERNAL_STORAGE

 //通过contentprovider向媒体库写入图片数据
    private suspend fun savePhotoToExternalStorage(displayName: String, bmp: Bitmap): Boolean {
        return withContext(Dispatchers.IO) {
            val imageCollection = sdk29AndUp {
                MediaStore.Images.Media.getContentUri(MediaStore.VOLUME_EXTERNAL_PRIMARY)
            } ?: MediaStore.Images.Media.EXTERNAL_CONTENT_URI

            val contentValues = ContentValues().apply {
                put(MediaStore.Images.Media.DISPLAY_NAME, "$displayName.jpg")
                put(MediaStore.Images.Media.MIME_TYPE, "image/jpeg")
                put(MediaStore.Images.Media.WIDTH, bmp.width)
                put(MediaStore.Images.Media.HEIGHT, bmp.height)
            }
            try {
                contentResolver.insert(imageCollection, contentValues)?.also { uri ->
                    //前面只是加了数据库的值，返回了UIR，
                    //然后我们需要将返回的URI中，写入图片数据
                    contentResolver.openOutputStream(uri).use { outputStream ->
                        if(!bmp.compress(Bitmap.CompressFormat.JPEG, 95, outputStream)) {
                            throw IOException("Couldn't save bitmap")
                        }
                    }
                } ?: throw IOException("Couldn't create MediaStore entry")
                true
            } catch(e: IOException) {
                e.printStackTrace()
                false
            }
        }
    }

删除外部文件

//这里会比较不一样，早期的版本可以直接删除
//Android10之后需要有权限
//没有权限，则需要创建删除请求，系统会有弹窗，让用户来进行确认

 private suspend fun deletePhotoFromExternalStorage(photoUri: Uri) {
        withContext(Dispatchers.IO) {
            try {
                contentResolver.delete(photoUri, null, null)
            } catch (e: SecurityException) {
                val intentSender = when {
                    Build.VERSION.SDK_INT >= Build.VERSION_CODES.R -> {
                        MediaStore.createDeleteRequest(contentResolver, listOf(photoUri)).intentSender
                    }
                    Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q -> {
                        val recoverableSecurityException = e as? RecoverableSecurityException
                        recoverableSecurityException?.userAction?.actionIntent?.intentSender
                    }
                    else -> null
                }
                intentSender?.let { sender ->
                    intentSenderLauncher.launch(
                        IntentSenderRequest.Builder(sender).build()
                    )
                }
            }
        }
    }