FileReader (GWT 2.6.1)

All Superinterfaces:

EventTarget

All Known Implementing Classes:

JsFileReader
```
public interface FileReader
extends EventTarget
```
The FileReader object lets web applications asynchronously read the contents of files (or raw data buffers) stored on the user's computer, using File or Blob objects to specify the file or data to read. File objects may be obtained in one of two ways: from a FileList object returned as a result of a user selecting files using the <input> element, or from a drag and drop operation's DataTransfer object.

To create a FileReader, simply do the following:
```
var reader = new FileReader();
```
See Using files from web applications for details and examples.

Field Summary

Fields
Modifier and Type	Field and Description
`static int`	`DONE` The entire read request has been completed.
`static int`	`EMPTY` No data has been loaded yet.
`static int`	`LOADING` Data is currently being loaded.

Method Summary

Methods
Modifier and Type	Method and Description
`void`	`abort()` Aborts the read operation.
`EventRemover`	`addEventListener(String type, EventListener listener)` Register an event handler of a specific event type on the `EventTarget`.
`EventRemover`	`addEventListener(String type, EventListener listener, boolean useCapture)` Register an event handler of a specific event type on the `EventTarget`.
`boolean`	`dispatchEvent(Event evt)` Dispatch an event to this `EventTarget`.
`FileError`	`getError()` The error that occurred while reading the file.
`EventListener`	`getOnabort()` Called when the read operation is aborted.
`EventListener`	`getOnerror()` Called when an error occurs.
`EventListener`	`getOnload()` Called when the read operation is successfully completed.
`EventListener`	`getOnloadend()` Called when the read is completed, whether successful or not.
`EventListener`	`getOnloadstart()` Called when reading the data is about to begin.
`EventListener`	`getOnprogress()` Called periodically while the data is being read.
`int`	`getReadyState()` Indicates the state of the `FileReader`.
`Object`	`getResult()` The file's contents.
`void`	`readAsArrayBuffer(Blob blob)`
`void`	`readAsBinaryString(Blob blob)` Starts reading the contents of the specified `Blob` , which may be a `File` .
`void`	`readAsDataURL(Blob blob)` Starts reading the contents of the specified `Blob` or `File` .
`void`	`readAsText(Blob blob)` Starts reading the specified blob's contents.
`void`	`readAsText(Blob blob, String encoding)` Starts reading the specified blob's contents.
`void`	`removeEventListener(String type, EventListener listener)` Removes an event listener from the `EventTarget`.
`void`	`removeEventListener(String type, EventListener listener, boolean useCapture)` Removes an event listener from the `EventTarget`.
`void`	`setOnabort(EventListener arg)`
`void`	`setOnerror(EventListener arg)`
`void`	`setOnload(EventListener arg)`
`void`	`setOnloadend(EventListener arg)`
`void`	`setOnloadstart(EventListener arg)`
`void`	`setOnprogress(EventListener arg)`

- Field Detail
  - DONE
```
static final int DONE
```
    The entire read request has been completed.
    
    See Also:
    Constant Field Values
  - EMPTY
```
static final int EMPTY
```
    No data has been loaded yet.
    
    See Also:
    Constant Field Values
  - LOADING
```
static final int LOADING
```
    Data is currently being loaded.
    
    See Also:
    Constant Field Values
- Method Detail
  - getError
```
FileError getError()
```
    The error that occurred while reading the file. Read only.
  - getOnabort
```
EventListener getOnabort()
```
    Called when the read operation is aborted.
  - setOnabort
```
void setOnabort(EventListener arg)
```
  - getOnerror
```
EventListener getOnerror()
```
    Called when an error occurs.
  - setOnerror
```
void setOnerror(EventListener arg)
```
  - getOnload
```
EventListener getOnload()
```
    Called when the read operation is successfully completed.
  - setOnload
```
void setOnload(EventListener arg)
```
  - getOnloadend
```
EventListener getOnloadend()
```
    Called when the read is completed, whether successful or not. This is called after either onload or onerror.
  - setOnloadend
```
void setOnloadend(EventListener arg)
```
  - getOnloadstart
```
EventListener getOnloadstart()
```
    Called when reading the data is about to begin.
  - setOnloadstart
```
void setOnloadstart(EventListener arg)
```
  - getOnprogress
```
EventListener getOnprogress()
```
    Called periodically while the data is being read.
  - setOnprogress
```
void setOnprogress(EventListener arg)
```
  - getReadyState
```
int getReadyState()
```
    Indicates the state of the FileReader. This will be one of the State constants. Read only.
  - getResult
```
Object getResult()
```
    The file's contents. This property is only valid after the read operation is complete, and the format of the data depends on which of the methods was used to initiate the read operation. Read only.
  - abort
```
void abort()
```
    Aborts the read operation. Upon return, the readyState will be DONE.
    
    Parameters
    
    None.
    
    Exceptions thrown
    
    DOM_FILE_ABORT_ERR
    
    abort() was called while no read operation was in progress (that is, the state wasn't LOADING).
    Note: This exception was not thrown by Gecko until Gecko 6.0 (Firefox 6.0 / Thunderbird 6.0 / SeaMonkey 2.3) .
  - addEventListener
```
EventRemover addEventListener(String type,
                            EventListener listener)
```
    Description copied from interface: EventTarget
    
    Register an event handler of a specific event type on the EventTarget.
    
    Specified by:
    
    addEventListener in interface EventTarget
  - addEventListener
```
EventRemover addEventListener(String type,
                            EventListener listener,
                            boolean useCapture)
```
    Description copied from interface: EventTarget
    
    Register an event handler of a specific event type on the EventTarget.
    
    Specified by:
    
    addEventListener in interface EventTarget
  - dispatchEvent
```
boolean dispatchEvent(Event evt)
```
    Description copied from interface: EventTarget
    
    Dispatch an event to this EventTarget.
    
    Specified by:
    
    dispatchEvent in interface EventTarget
  - readAsArrayBuffer
```
void readAsArrayBuffer(Blob blob)
```
    Starts reading the contents of the specified Blob or File . When the read operation is finished, the readyState will become DONE, and the onloadend callback, if any, will be called. At that time, the result attribute contains an ArrayBuffer representing the file's data.
    
    Parameters
    
    blob
    
    The DOM Blob or File to read into the ArrayBuffer.
  - readAsBinaryString
```
void readAsBinaryString(Blob blob)
```
    Starts reading the contents of the specified Blob , which may be a File . When the read operation is finished, the readyState will become DONE, and the onloadend callback, if any, will be called. At that time, the result attribute contains the raw binary data from the file.
    
    Parameters
    
    blob
    
    The DOM Blob or File from which to read.
  - readAsDataURL
```
void readAsDataURL(Blob blob)
```
    Starts reading the contents of the specified Blob or File . When the read operation is finished, the readyState will become DONE, and the onloadend callback, if any, will be called. At that time, the result attribute contains a data: URL representing the file's data.
    
    This method is useful, for example, to get a preview of an image before uploading it:
```
<!doctype html>
<html>
<head>
<meta content="text/html; charset=UTF-8" http-equiv="Content-Type" />
<title>Image preview example</title>
<script type="text/javascript">
oFReader = new FileReader(), rFilter = /^(image\/bmp|image\/cis-cod|image\/gif|image\/ief|image\/jpeg|image\/jpeg|image\/jpeg|image\/pipeg|image\/png|image\/svg\+xml|image\/tiff|image\/x-cmu-raster|image\/x-cmx|image\/x-icon|image\/x-portable-anymap|image\/x-portable-bitmap|image\/x-portable-graymap|image\/x-portable-pixmap|image\/x-rgb|image\/x-xbitmap|image\/x-xpixmap|image\/x-xwindowdump)$/i;

oFReader.onload = function (oFREvent) {
  document.getElementById("uploadPreview").src = oFREvent.target.result;
};

function loadImageFile() {
  if (document.getElementById("uploadImage").files.length === 0) { return; }
  var oFile = document.getElementById("uploadImage").files[0];
  if (!rFilter.test(oFile.type)) { alert("You must select a valid image file!"); return; }
  oFReader.readAsDataURL(oFile);
}
</script>
</head>

<body onload="loadImageFile();">
<form name="uploadForm">
<table>
<tbody>
<tr>
<td><img id="uploadPreview" style="width: 100px; height: 100px;" src="data:image/svg+xml,%3C%3Fxml%20version%3D%221.0%22%3F%3E%0A%3Csvg%20width%3D%22153%22%20height%3D%22153%22%20xmlns%3D%22http%3A//www.w3.org/2000/svg%22%3E%0A%20%3Cg%3E%0A%20%20%3Ctitle%3ENo%20image%3C/title%3E%0A%20%20%3Crect%20id%3D%22externRect%22%20height%3D%22150%22%20width%3D%22150%22%20y%3D%221.5%22%20x%3D%221.500024%22%20stroke-width%3D%223%22%20stroke%3D%22%23666666%22%20fill%3D%22%23e1e1e1%22/%3E%0A%20%20%3Ctext%20transform%3D%22matrix%286.66667%2C%200%2C%200%2C%206.66667%2C%20-960.5%2C%20-1099.33%29%22%20xml%3Aspace%3D%22preserve%22%20text-anchor%3D%22middle%22%20font-family%3D%22Fantasy%22%20font-size%3D%2214%22%20id%3D%22questionMark%22%20y%3D%22181.249569%22%20x%3D%22155.549819%22%20stroke-width%3D%220%22%20stroke%3D%22%23666666%22%20fill%3D%22%23000000%22%3E%3F%3C/text%3E%0A%20%3C/g%3E%0A%3C/svg%3E" alt="Image preview" /></td>
<td><input id="uploadImage" type="file" name="myPhoto" onchange="loadImageFile();" /></td>
</tr>
</tbody>
</table>
<p><input type="submit" value="Send" /></p>
</form>
</body>
</html>
```
    Parameters
    
    file
    
    The DOM Blob or File from which to read.
  - readAsText
```
void readAsText(Blob blob)
```
    Starts reading the specified blob's contents. When the read operation is finished, the readyState will become DONE, and the onloadend callback, if any, will be called. At that time, the result attribute contains the contents of the file as a text string.
    
    Parameters
    
    blob
    
    The DOM Blob or File from which to read.
    
    encoding Optional
    
    A string indicating the encoding to use for the returned data. By default, UTF-8 is assumed if this parameter is not specified.
  - readAsText
```
void readAsText(Blob blob,
              String encoding)
```
    Starts reading the specified blob's contents. When the read operation is finished, the readyState will become DONE, and the onloadend callback, if any, will be called. At that time, the result attribute contains the contents of the file as a text string.
    
    Parameters
    
    blob
    
    The DOM Blob or File from which to read.
    
    encoding Optional
    
    A string indicating the encoding to use for the returned data. By default, UTF-8 is assumed if this parameter is not specified.
  - removeEventListener
```
void removeEventListener(String type,
                       EventListener listener)
```
    Description copied from interface: EventTarget
    
    Removes an event listener from the EventTarget.
    
    Specified by:
    
    removeEventListener in interface EventTarget
  - removeEventListener
```
void removeEventListener(String type,
                       EventListener listener,
                       boolean useCapture)
```
    Description copied from interface: EventTarget
    
    Removes an event listener from the EventTarget.
    
    Specified by:
    
    removeEventListener in interface EventTarget

Interface FileReader

Field Summary

Method Summary

Field Detail

DONE

EMPTY

LOADING

Method Detail

getError

getOnabort

setOnabort

getOnerror

setOnerror

getOnload

setOnload

getOnloadend

setOnloadend

getOnloadstart

setOnloadstart

getOnprogress

setOnprogress

getReadyState

getResult

abort

Parameters

Exceptions thrown

addEventListener

addEventListener

dispatchEvent

readAsArrayBuffer

Parameters

readAsBinaryString

Parameters

readAsDataURL

Parameters

readAsText

Parameters

readAsText

Parameters

removeEventListener

removeEventListener