B4J Tutorial [BANano] BANanoFiles - A nifty way to read a file text contents without uploading to the server


Licensed User

2010-05-09 Update


A Skeleton based demo is attached.

I was checking the BANanoPromise example code as I needed a way to get a text file contents without having to upload to the server and the process it.

So I extracted some portions of that code out and saved them in a class. Here is the class code:

public Sub readAsText(fr As String) As BANanoPromise
    Dim promise As BANanoPromise 'ignore
    ' calling a single upload
    promise.CallSub(Me, "ReadFileAsText", Array(fr))
    Return promise
End Sub

private Sub ReadFileAsText(FileToRead As Object)
    ' make a filereader
    Dim FileReader As BANanoObject
    FileReader.Initialize2("FileReader", Null)
    ' attach the file (to get the name later)
    FileReader.SetField("file", FileToRead)
    ' make a callback for the onload event
    ' an onload of a FileReader requires a 'event' param
    Dim event As Map
    FileReader.SetField("onload", BANano.CallBack(Me, "OnLoad", Array(event)))
    FileReader.SetField("onerror", BANano.CallBack(Me, "OnError", Array(event)))
    ' start reading the DataURL
    FileReader.RunMethod("readAsText", FileToRead)
End Sub

private Sub OnLoad(event As Map) As String 'ignore
    ' getting our file again (set in UploadFileAndGetDataURL)
    Dim FileReader As BANanoObject = event.Get("target")
    Dim UploadedFile As BANanoObject = FileReader.GetField("file")
    ' return to the then of the UploadFileAndGetDataURL
    BANano.ReturnThen(CreateMap("name": UploadedFile.GetField("name"), "result": FileReader.Getfield("result")))
End Sub

private Sub OnError(event As Map) As String 'ignore
    Dim FileReader As BANanoObject = event.Get("target")
    Dim UploadedFile As BANanoObject = FileReader.GetField("file")
    Dim Abort As Boolean = False
    ' uncomment this if you want to abort the whole operatio
    ' Abort = true
    ' FileReader.RunMethod("abort", Null)
    BANano.ReturnElse(CreateMap("name": UploadedFile.GetField("name"), "result": FileReader.GetField("error"), "abort": Abort))
End Sub
To use this one needs a file input control and trap the change event. I think we know how that can be done.

Here is how I have used it, my class name where the above code is saved is called vm, a banano library compilation.

We have created a skeleton based layout and then we add our invisible file selector here.

Define class in process globals

Private bf As BANanoFiles
Add our invisible component

bf.Initialize.AddFileSelect(Me, "body", "fuconnect")
When a button is clicked, activate the file select

Sub btnReadText_Click (event As BANanoEvent)
End Sub
Then trap the file selector change event and read the contents of the file

Sub fuconnect_change(e As BANanoEvent)
    Dim fileList As List = bf.GetFileListFromTarget(e)
    'no file is selected
    If fileList.size = 0 Then Return
    'only process 1 file
    Dim fr As String = fileList.get(0)
    Dim Result As Map
    Dim promise As BANanoPromise = bf.readAsText(fr)
        'get the json content
        Dim txt As String = Result.get("result")
        Dim compError As String = Result.get("result")
    'nully file component so we can select same file
End Sub


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