display png file in shinyR - r

Question

I am trying to display a png file using shiny. file is uploaded but not displayed properly. I have included both ui and server code
ui <- fluidPage(
titlePanel("Upload Slide Image"),
sidebarLayout(
sidebarPanel(fileInput("file1", "Choose png File", multiple = TRUE,
accept = c(".png")) ), # Input: Select a file ----
mainPanel(imageOutput("myImage"))
)
)
server <- function(input, output, session){
output$myImage <- renderImage({
outfile <- tempfile(fileext = '.png')
png(outfile, width = 400, height = 300) # Generate the PNG
dev.off()
list(src = outfile,contentType = 'image/png',width = 400, height = 300,
alt = "This is alternate text")
}, deleteFile = TRUE)
}
# Create Shiny app ----
shinyApp(ui, server)

Answer 1

You are not doing anything with input (as mentioned by #RolandASc). Rather you are generating a new png file in your server.
As a source, you need to add input$file1$datapath to use the file that has been uploaded using the UI, as mentioned in this answer.
ui <- fluidPage(
titlePanel("Upload Slide Image"),
sidebarLayout(
sidebarPanel(fileInput("file1", "Choose png File", multiple = TRUE,
accept = c(".png")) ), # Input: Select a file ----
mainPanel(imageOutput("myImage"))
)
)
server <- function(input, output, session){
observe({
if (is.null(input$file1)) return()
output$myImage <- renderImage({
## Following three lines CREATE a NEW image. You do not need them
#outfile <- tempfile(fileext = '.png')
#png(outfile, width = 400, height = 300) # Generate the PNG
#dev.off()
list(src = input$file1$datapath, contentType = 'image/png',width = 400, height = 300,
alt = "This is alternate text")
}, deleteFile = TRUE)
})
}
# Create Shiny app ----
shinyApp(ui, server)
EDIT: I have added a check in observe to cater for error when the app is first run.