zk 的Fileupload 一直返回NULL 解决办法
2012-02-25 09:42 OOA 阅读(1979) 评论(0) 编辑 收藏 举报昨天想用Fileupload 控件，可是，上传上去的文件，根本获取不到，从网上查了查，都不行。调试发现，线程没有被阻塞，所以get（）方法总是返回null，最后上了官方找到了解决方法。就是捕获Upload事件来获取上传的文件。以下是官方的说明：http://books.zkoss.org/wiki/ZK_Component_Reference/Essential_Components/Fileupload#Event_Thread_Disabled
ZK Component Reference/Essential Components/Fileupload
From Documentation
Jump to: navigation, search
Search this book:
TOC
Essential Components 
Filedownload 
Contents
[hide]- 1 Fileupload
- 2 Employment/Purpose
- 3 Example
- 4 Supported Events
- 5 Supported Children
- 6 Use Cases
- 7 Version History
Fileupload
- Demonstration: File Upload
- Java API: Fileupload
- JavaScript API: Fileupload
- Style Guide: N/A
Employment/Purpose
There are two ways to use Fileupload as a component to upload files, or invoke Fileupload.get() to open a dialog to upload files.
Use as a Component
Fileupload itself is a component. You can use it directly as follows.
<fileupload label="Upload">
<attribute name="onUpload">
org.zkoss.util.media.Media media = event.getMedia();
//then, you can process media here
</attribute>
</fileupload>
Fileupload is actually a button with upload=true. In other words, the above is equivalent to
<button label="Upload" upload="true">
...
Please refer to Button: Upload for details.
Invoke the Static Method: get
Fileupload provides a set of static methods to simplify file uploading, such as Fileupload.get(), Fileupload.get(String, String), and so on.
The behavior is a little bit different depending on if the event thread is enabled (default: it is disabled[1]).
- ↑ Prior to 5.0, it is default to enabled. Refer to ZK Configuration Reference: disable-event-thread.
Event Thread Disabled
When the event thread is disabled (default), the execution won't be suspended when Fileupload.get() is called. In other words, the returned value is always null. To retrieve the uploaded files, the developer has to listen the onUpload event, which is sent when the uploading is completed.
By default, the onUpload event is sent to all root components. For example, Div will, in the following example, receive the onUpload event since it is the root component:（关键的地方）
<div onUpload="processMedia(event.getMedias());">
<zscript deferred="true"><![CDATA[
import org.zkoss.util.media.Media;
public void processMedia(Media[] media) {
if (media != null) {
for (int i = 0; i < media.length; i++) {
if (media[i] instanceof org.zkoss.image.Image) {
image.setContent(media[i]);
} else {
Messagebox.show("Not an image: " + media[i], "Error",
Messagebox.OK, Messagebox.ERROR);
break; //not to show too many errors
}
}
}
}
]]></zscript>
<vbox>
<button label="Upload" onClick="Fileupload.get(-1);" />
<image id="image" />
</vbox>
</div>
Specify the Target Component
[Since 5.0.2]
If you prefer the event being sent to a particular component, specify the component in the desktop's attribute calledorg.zkoss.zul.Fileupload.target.
For example, we could have the button to receive the onUpload event as follows:
<zk>
<zscript deferred="true"><![CDATA[
import org.zkoss.util.media.Media;
Executions.getCurrent().getDesktop().setAttribute(
"org.zkoss.zul.Fileupload.target", uploadBtn);
public void processMedia(Media[] media) {
if (media != null) {
for (int i = 0; i < media.length; i++) {
if (media[i] instanceof org.zkoss.image.Image) {
image.setContent(media[i]);
} else {
Messagebox.show("Not an image: " + media[i], "Error",
Messagebox.OK, Messagebox.ERROR);
break; //not to show too many errors
}
}
}
}
]]></zscript>
<vbox>
<button id="uploadBtn" label="Upload"
onUpload="processMedia(event.getMedias());"
onClick="Fileupload.get(-1);" />
<image id="image" />
</vbox>
</zk>
Event Thread Enabled
If the event thread is enable, the uploaded file will be returned directly by Fileupload.get() and other static methods, such as:
<zk>
<button label="Upload">
<attribute name="onClick">{
org.zkoss.util.media.Media[] media = Fileupload.get(-1);
if (media != null) {
for (int i = 0; i < media.length; i++) {
if (media[i] instanceof org.zkoss.image.Image) {
org.zkoss.zul.Image image = new org.zkoss.zul.Image();
image.setContent(media[i]);
image.setParent(pics);
} else {
Messagebox.show("Not an image: "+media[i], "Error", Messagebox.OK, Messagebox.ERROR);
break; //not to show too many errors
}
}
}
}</attribute>
</button>
<vbox id="pics" />
</zk>
As shown, Fileupload.get(int) won't return until the end user uploads the files (and/or closes the dialog).
Example
Here is an example that uses Fileupload as a component:
<image id="img" />
Upload your hot shot:
<fileupload label="Upload" onUpload="img.setContent(event.media)" />
Supported Events
Name
Event Type
None
None
- Inherited Supported Events: Button
Supported Children
*NONE
Use Cases
Version
Description
Example Location
Version History
Last Update : 2011/7/29
Version
Date
Content
5.0.2
May 2010
Able to specify a target for the onUpload event sent by Fileupload.get(). Used if the event thread is disabled.
