Problems with tutorial: "Creating a Web Dynpro Tree"

[Former Member]

Hi!

I'm a rookie and therefore I'm practicing on compleating some tutorials like "Creating a Web Dynpro Tree" (https://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/f0ec6622-8da5-2a10-349b-868b6a553efa)

I did just as the tutorial told me to (I think) but still I get a java.lang.NullPointerException when I deploy and run my application.

In the bold line is where it is something wrong:

public static void wdDoModifyView(IPrivateTreeView wdThis, IPrivateTreeView.IContextNode wdContext, com.sap.tc.webdynpro.progmodel.api.IWDView view, boolean firstTime)

{

//@@begin wdDoModifyView

if (firstTime) {

IWDTreeNodeType treeNode = (IWDTreeNodeType) view.getElement("TreeNodeType");

/* parameter mapping from parameter "path" to

• parameter "selectedElement"

*/

treeNode._mappingOfOnAction()._addSourceMapping("path", "selectedElement");

/* parameter mapping from parameter "path" to

• parameter "element".

*/

treeNode._mappingOfOnLoadChildren()._addSourceMapping("path","element");

}

//@@end

}

What I don't understand is what the function/meaning of the parameter path is. The parameters selectedElement and element I do recognize and have written. And I don't understand why there is a difference between the two underscored line of code (see above) even though the comments claim that it does the same kind of mapping.

Best regards

/Johan

[Former Member · Accepted solution]

I never saw a method named "_addSourceMapping()".

Verify that the TreeNodeType instance has exactly the same ID (case-sensitive) than given in the string literal. The "path" parameter will give you the context path describing the tree node. Alternatively you can use the (implicit) parameter named "nodeElement".

Armin

[Former Member · Accepted solution]

I tried to get "addSourceMapping()." underscored so people would better understand what I was referring to but it didn't work and that's why it looked weired.

Thanks for your help Armin, now it works fine.

It was as you said.

if (firstTime) {

IWDTreeNodeType treeNode = (IWDTreeNodeType) view.getElement("TreeNodeType");

When I changed "TreeNodeType" to it's real ID, "TheNode" I didn't get a nullPointerException. I think it must be wrong in the tutorial because I followed the instructions which said to name it "TheNode" but then the author mus have forgot to change it from the default ID ("TreeNodeType").

Best Regards!

/Johan

[Former Member · Accepted solution]

I don't know which version you are using, but if available, better use the "Parameter Mapping" editor (Right-click UI element in "Outline") than the old hack in wdDoModifyView(). This avoids those issues with using string literals.

Armin

[Former Member · Accepted solution]

I'm using Web Dynpro Java in SAP NetWeaver 7.1, so I guess that option is available to me.

Thanks for the tip, to bad I can't give you anymore points 😄

/Johan

[Former Member]

[clarification to message above]

if (firstTime) {

IWDTreeNodeType treeNode = (IWDTreeNodeType) view.getElement("TreeNodeType");

/* parameter mapping from parameter "path" to

• parameter "selectedElement"

*/

treeNode.mappingOfOnAction().addSourceMapping("path", "selectedElement");

/* parameter mapping from parameter "path" to

• parameter "element".

*/

treeNode.mappingOfOnLoadChildren().addSourceMapping("path","element");

}

The bold pieces of code is, according to the comments, supposed to do the same kind of mapping even though there is a difference between them other than the parameter names.