图片下载及保存

1. 确定文件的下载路径，context.getExternalFilesDir(“images”)，即app外部存储的files路径，无须动态权限声明
2. 创建URL对象，val url = URL(path)，由图片的下载地址创建
3. 通过url.openConnection()打开连接，获取连接对象
4. 连接conn.connect()
5. 获取输入流，val input: InputStream = conn.getInputStream()
6. 创建输出流，准备写入val fos = FileOutputStream(out)
7. 标准io操作，将读到的字节写入到文件中

try {
    val buf = ByteArray(1024)
    var numRead: Int
    fos.run {
        while ((input.read(buf).also { numRead = it }) != -1) {
            write(buf, 0, numRead)
        }
        flush()
    }
} catch (ex: Exception) {
    ex.printStackTrace()
} finally {
    input.close()
    fos.close()
}

//保存图片到系统相册
/**
* Q以上保存到系统相册中
*/
private fun saveToPicture(name: String, file: File) {
    val values = ContentValues().apply {
        put(MediaStore.Images.Media.DISPLAY_NAME, name)
        put(MediaStore.Images.Media.DESCRIPTION, "This is a alarm pic")
        put(MediaStore.Images.Media.MIME_TYPE, "image/jpeg")
        put(MediaStore.Images.Media.TITLE, "Image.jpg")
        put(MediaStore.Images.Media.RELATIVE_PATH, "Pictures/")
    }
    val external = MediaStore.Images.Media.EXTERNAL_CONTENT_URI
    val resolver = PlatinDriveApp.instance.contentResolver
    val insertUri = resolver.insert(external, values)
    var inputStream: BufferedInputStream? = null
    var outputStream: OutputStream? = null
    try {
        inputStream = BufferedInputStream(FileInputStream(file))
        insertUri?.let {
            outputStream = resolver.openOutputStream(it)
        }
        outputStream?.run {
            val buffer = ByteArray(1024 * 4)
            var len: Int
            while ((inputStream.read(buffer).also { len = it }) != -1) {
                write(buffer, 0, len)
            }
            flush()
        }
    } catch (e: IOException) {
        e.printStackTrace()
    } finally {
        inputStream?.close()
        outputStream?.close()
    }
}