Android - App keeps crashing with error - I think it has to do with Preference Fragments

Question

I keep getting an error that has to do with the preferences and I know it has depreciated so I looked here for help http://developer.android.com/reference/android/preference/PreferenceFragment.html

and I did exactly as it says on the bottom part...

Here is the error:

12-04 00:39:37.553: E/AndroidRuntime(1164): FATAL EXCEPTION: main
12-04 00:39:37.553: E/AndroidRuntime(1164): Process: com.proteintracker, PID: 1164
12-04 00:39:37.553: E/AndroidRuntime(1164): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.proteintracker/com.proteintracker.MainPreferenceActivity}: java.lang.ClassCastException: com.proteintracker.MainPreferenceActivity cannot be cast to android.app.Activity
12-04 00:39:37.553: E/AndroidRuntime(1164):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2102)
12-04 00:39:37.553: E/AndroidRuntime(1164):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2226)
12-04 00:39:37.553: E/AndroidRuntime(1164):     at android.app.ActivityThread.access$700(ActivityThread.java:135)
12-04 00:39:37.553: E/AndroidRuntime(1164):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1397)
12-04 00:39:37.553: E/AndroidRuntime(1164):     at android.os.Handler.dispatchMessage(Handler.java:102)
12-04 00:39:37.553: E/AndroidRuntime(1164):     at android.os.Looper.loop(Looper.java:137)
12-04 00:39:37.553: E/AndroidRuntime(1164):     at android.app.ActivityThread.main(ActivityThread.java:4998)
12-04 00:39:37.553: E/AndroidRuntime(1164):     at java.lang.reflect.Method.invokeNative(Native Method)
12-04 00:39:37.553: E/AndroidRuntime(1164):     at java.lang.reflect.Method.invoke(Method.java:515)
12-04 00:39:37.553: E/AndroidRuntime(1164):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
12-04 00:39:37.553: E/AndroidRuntime(1164):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
12-04 00:39:37.553: E/AndroidRuntime(1164):     at dalvik.system.NativeStart.main(Native Method)
12-04 00:39:37.553: E/AndroidRuntime(1164): Caused by: java.lang.ClassCastException: com.proteintracker.MainPreferenceActivity cannot be cast to android.app.Activity
12-04 00:39:37.553: E/AndroidRuntime(1164):     at android.app.Instrumentation.newActivity(Instrumentation.java:1061)
12-04 00:39:37.553: E/AndroidRuntime(1164):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2093)
12-04 00:39:37.553: E/AndroidRuntime(1164):     ... 11 more

Here is my code for the Preference class

    package com.proteintracker;

import android.app.Activity;
import android.os.Bundle;

public class MainPreferenceActivity extends Activity {

      @Override
      public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
       // Display the fragment as the main content.
          getFragmentManager().beginTransaction()
                  .replace(android.R.id.content, new MainPreferenceFragment())
                  .commit();

      }
}

Here is my code for the preference fragment class:

package com.proteintracker;

import android.os.Bundle;
import android.preference.PreferenceFragment;

public class MainPreferenceFragment extends PreferenceFragment {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Load the preferences from an XML resource
        addPreferencesFromResource(R.xml.main_preferences);
    }
}

Here is my xml file for it

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android" android:orderingFromXml="true">

    <EditTextPreference
        android:dialogMessage="Enter grams"
        android:dialogTitle="Protein Grams"
        android:key="gramsPerDay"
        android:title="Grams per day" />

</PreferenceScreen>

and here is the manifest file:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.proteintracker"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="11"
        android:targetSdkVersion="18" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        >
        <activity android:name="MainActivity"><intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter></activity><activity
            android:name="MainPreferenceActivity"
            android:label="@string/app_name" >
        </activity>
        <activity android:name="HelpActivity"></activity>

    </application>

</manifest>

EDIT---

Here is my main activity file:

package com.proteintracker;

import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends Activity {

    private OnClickListener buttonListener = new OnClickListener() {

        @Override
        public void onClick(View v) {
            EditText editText = (EditText)findViewById(R.id.editText1);
            Log.d("ProteinTracker", editText.getText().toString());
        }
    };
    private OnClickListener helpButtonListener = new OnClickListener() {

        @Override
        public void onClick(View v) {

            SharedPreferences preferences = getSharedPreferences("default", MODE_PRIVATE);
            String value = preferences.getString("activityTest", "");
            Log.d("ProteinTracker", value);


            Intent intent = new Intent(MainActivity.this, MainPreferenceActivity.class);
            startActivity(intent);

        }
    };



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if(savedInstanceState != null) {
            Log.d("ProteinTracker", savedInstanceState.getString("keyName"));
        }
        TextView textView = (TextView) findViewById(R.id.mainActivityTextView);
        textView.setText(R.string.test_updating_a_view);

        Button button = (Button)findViewById(R.id.button1);
        button.setOnClickListener(buttonListener );

        Button helpButton = (Button)findViewById(R.id.helpButton);
        helpButton.setOnClickListener(helpButtonListener );

        SharedPreferences preferences = getSharedPreferences("default", MODE_PRIVATE);
        Editor editor = preferences.edit();
        editor.putString("activityTest", "activity value");
        editor.commit();

    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        outState.putString("keyName","string");
        super.onSaveInstanceState(outState);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {

        MenuInflater menuInflater = getMenuInflater();
        menuInflater.inflate(R.menu.main_menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        switch(item.getItemId()) {
            case R.id.settingsMenuItem:
                //launch settings activity

            default:
        }

        return super.onOptionsItemSelected(item);
    }



}

I updated the fragment file and added a new one too and also, have included my main activity file.

I am not sure what I need to do, I am new at Java and Android... thanks!

Answer 1

Fragments need to be added to activities. You should change the name of your fragment from MainPreferenceActivity to MainPreferenceFragment, so you'd have:

public class MainPreferenceFragment extends PreferenceFragment {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // Load the preferences from an XML resource
        addPreferencesFromResource(R.xml.main_preferences);
    }
}

and then have MainPreferenceActivity extending Activity, where you add your fragment:

public class MainPreference Activity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // Display the fragment as the main content.
    getFragmentManager().beginTransaction()
            .replace(android.R.id.content, new MainPreferenceFragment())
            .commit();
    }
}

Read more here.