Android: ClassCastException when adding a header view to ExpandableListView

问题

I'm trying to add a header to an ExpandableListView like so:

headerView = View.inflate(this, R.layout.header, null);
expandableListView.addHeaderView(headerView);
expandableListView.setAdapter(new SectionedAdapter(this));

Which gives me the following error:

 12-08 16:23:42.354:
 ERROR/AndroidRuntime(421): Caused by:java.lang.ClassCastException: android.widget.LinearLayout$LayoutParams
 12-08 16:23:42.354:   ERROR/AndroidRuntime(421): at android.widget.ListView.clearRecycledState(ListView.java:504)
 12-08 16:23:42.354: ERROR/AndroidRuntime(421): at android.widget.ListView.resetList(ListView.java:490)
 12-08 16:23:42.354:ERROR/AndroidRuntime(421):at android.widget.ListView.setAdapter(ListView.java:422)
 12-08 16:23:42.354:ERROR/AndroidRuntime(421): at android.widget.ExpandableListView.setAdapter(ExpandableListView.java:475)

This is happening at the call to expandableListView.setAdapter(new SectionedAdapter(this)), but I can't figure out why. Any ideas?

回答1:

Ok, I figured this one out. I got rid of the runtime error by programatically setting the View's LayoutParams to ListView LayoutParams, like so:

headerView.setLayoutParams(new ListView.LayoutParams(ListView.LayoutParams.FILL_PARENT, ListView.LayoutParams.WRAP_CONTENT));

before adding the view. The reason being is found in the Android docs:

http://developer.android.com/reference/android/view/View.html#setLayoutParams(android.view.ViewGroup.LayoutParams)

which states that:

These supply parameters to the parent of this view specifying how it should be arranged. There are many subclasses of ViewGroup.LayoutParams, and these correspond to the different subclasses of ViewGroup that are responsible for arranging their children.

So basically, if you are adding a view to another, you MUST set the LayoutParams of the view to the LayoutParams type that the parent uses, or you will get a runtime error.

回答2:

Even though the above answer might work for many, there is still a better explanation. ClassCastException is the normal behaviour after calling listview.addHeaderView or listview.addFooterView.

The reason is that the initial adapter is wrapped in the HeaderViewListAdapter. To get your adapter use this code.

YourAdapter ya = (YourAdapter) ((HeaderViewListAdapter)lv.getAdapter()).getWrappedAdapter();

Code taken from here

回答3:

In my case this didn't work. I had to set a footerView to my listView before setting it's adapter. First I initialized my loadingView from a layout file in OnCreate method:

LayoutInflater layoutInflater = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
loadingView = layoutInflater.inflate(R.layout.loading_view, null);

Then I used this workaround in the same method:

this.setIsLoading(true);
listView.setAdapter(adapter);
this.setIsLoading(false);

Where

private void setIsLoading(boolean isLoading)
{
    this.isLoading = isLoading;

    if (isLoading) {
        listView.addFooterView(loadingView);
    }
    else {
        listView.removeFooterView(loadingView);
    }
}

回答4:

You should put parent view to your inflated view.

ListView listview = (ListView) findViewById(R.id.listview);
headerView = View.inflate(this, R.layout.header, listview, false); // set listview as parent view
listview.addHeaderView(headerview);

来源：https://stackoverflow.com/questions/4393775/android-classcastexception-when-adding-a-header-view-to-expandablelistview

标签

android

android-linearlayout

expandablelistview

classcastexception