Eclipse Android error when switching to GUI xml - android-layout

Question

I get the following error when I switch from xml to GUI for a preferences layout file:
Exception raised during rendering: com.android.layoutlib.bridge.MockView cannot be cast to android.view.ViewGroup
Exception details are logged in Window > Show View > Error Log
The following classes could not be found:
- PreferenceCategory (Fix Build Path, Edit XML)
- PreferenceScreen (Fix Build Path, Edit XML)
My xml file looks like this:
<?xml version="1.0" encoding="UTF-8"?>
<PreferenceScreen
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
<PreferenceCategory
android:title="Activation">
<CheckBoxPreference
android:title="Title1"
android:defaultValue="false"
android:key="checkbox1">
</CheckBoxPreference>
</PreferenceCategory>
<PreferenceCategory
android:title="Option1">
<PreferenceScreen
android:title="Set Option">
<CheckBoxPreference
android:title="ENABLE OPTION"
android:defaultValue="false"
android:summary="text"
android:key="checkboxOption1">
</CheckBoxPreference>
<CheckBoxPreference
android:title="DISPLAY OPTIONS"
android:defaultValue="false"
android:summary="text"
android:key="checkboxDisplay1">
</CheckBoxPreference>
<EditTextPreference
android:title="OPTION2"
android:name="Option2"
android:summary="text"
android:defaultValue="1"
android:key="editOption2">
</EditTextPreference>
<CheckBoxPreference
android:title="OPTION3"
android:defaultValue="false"
android:summary="text"
android:key="checkboxOption3">
</CheckBoxPreference>
</PreferenceScreen>
</PreferenceCategory>
<PreferenceCategory
android:title="Option4">
<PreferenceScreen
android:title="Set Option4">
<CheckBoxPreference
android:title="OPTION4"
android:defaultValue="false"
android:summary=""
android:key="checkboxOption4">
</CheckBoxPreference>
<CheckBoxPreference
android:title="OPTION5"
android:defaultValue="false"
android:summary="text"
android:key="checkboxOption5">
</CheckBoxPreference>
<EditTextPreference
android:title="OPTION6"
android:name="Option6"
android:summary="text"
android:defaultValue="1"
android:key="editOption6">
</EditTextPreference>
<EditTextPreference
android:title="OPTION7"
android:name="Option7"
android:summary="text"
android:defaultValue="1"
android:key="editOption7">
</EditTextPreference>
<EditTextPreference
android:title="OPTION8"
android:name="Option8"
android:summary="text"
android:defaultValue="1"
android:key="editOption8">
</EditTextPreference>
</PreferenceScreen>
</PreferenceCategory>
<PreferenceCategory
android:title="OPTION9">
<PreferenceScreen
android:title="Option9">
<EditTextPreference
android:title="Option9"
android:name="Option9"
android:summary="text"
android:defaultValue=""
android:key="editOption9">
</EditTextPreference>
</PreferenceScreen>
</PreferenceCategory>
</PreferenceScreen>
Any assistance would be greatly appreciated

Answer 1

I had this problem because I treated the preference list like a normal activity. It's actually completely different. First, you need to move the XML file from res/layout to res/xml (in Eclipse, you have to create this folder manually). You also have to use different Java code:
import android.os.Bundle;
import android.preference.PreferenceActivity;
public class Settings extends PreferenceActivity { //NOT activity!
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Initialize the preference screen defined in /res/xml/preference.xml
addPreferencesFromResource(R.xml.preferences); //NOT setContentView
}
}
You'll get a warning for API level >=11 about addPreferencesFromResource being deprecated. That's because Android wants you to switch to a preference screen based on fragments ("PreferenceFragments"), which is a fair bit more complicated. There's an example here.