Dialog fragment cannot be cast to android.app.activity

Question

I am recreating the custom dialog layout on Android Developers. with minor tweaks. I am getting an issue telling me that the dialogfragment cannot be cast to android.app.activity. I am having trouble understandin why I am gettin this error in the logcat.

Logcat:

01-20 22:03:10.317: E/AndroidRuntime(9949): FATAL EXCEPTION: main
01-20 22:03:10.317: E/AndroidRuntime(9949): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.customdialogfragment/com.customdialogfragment.CustomDialogFragment}: java.lang.ClassCastException: com.customdialogfragment.CustomDialogFragment cannot be cast to android.app.Activity
01-20 22:03:10.317: E/AndroidRuntime(9949):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2004)

Activity

public class CustomDialogFragment extends DialogFragment {

    static CustomDialogFragment newInstance() {
        CustomDialogFragment newFragment = new CustomDialogFragment();
        return newFragment;
    }

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {

        AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
        LayoutInflater inflater = getActivity().getLayoutInflater();

        // Inflate and set the layout for the dialog
        // Pass null as the parent view because its going in the dialog layout
        builder.setView(
                inflater.inflate(R.layout.activity_custom_dialog_fragment, null))
                // Add action buttons
                .setPositiveButton("Sign In",
                        new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(DialogInterface dialog, int id) {
                                // sign in the user ...
                            }
                        })
                .setNegativeButton("Cancel",
                        new DialogInterface.OnClickListener() {
                            public void onClick(DialogInterface dialog, int id) {
                                CustomDialogFragment.this.getDialog().cancel();
                            }
                        });
        return builder.create();
    }

    public void showMyDialog() {
        CustomDialogFragment newFragment = new CustomDialogFragment();
        newFragment.show(getFragmentManager(), "custom");
    }
}

Manifest:

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

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="18" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.customdialogfragment.launcher"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

    </application>

</manifest>

XML

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="vertical" >

    <ImageView
        android:layout_width="match_parent"
        android:layout_height="64dp"
        android:background="#FFFFBB33"
        android:contentDescription="@string/app_name"
        android:scaleType="center"
        android:src="@drawable/ic_launcher" />

    <EditText
        android:id="@+id/username"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginBottom="4dp"
        android:layout_marginLeft="4dp"
        android:layout_marginRight="4dp"
        android:layout_marginTop="16dp"
        android:hint="username"
        android:inputType="textEmailAddress" />

    <EditText
        android:id="@+id/password"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginBottom="16dp"
        android:layout_marginLeft="4dp"
        android:layout_marginRight="4dp"
        android:layout_marginTop="4dp"
        android:fontFamily="sans-serif"
        android:hint="password"
        android:inputType="textPassword" />

</LinearLayout>

Answer 1

If you want to show your custom dialog fragment, you don't need to define it in the Manifest, rather you need to create an instance and call its show method in your activity. That's why you are receiving that error. You have in your manifest an activity defined: com.customdialogfragment.launcher, you need to create that activity and then create the fragment inside the activiy.

import android.os.Bundle;
import android.support.v4.app.FragmentActivity;

public class launcher extends FragmentActivity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_activity);

        showMyDialog();
    }

    public void showMyDialog() {    
      CustomDialogFragment newFragment = new CustomDialogFragment();
      newFragment.show(getSupportFragmentManager(), "custom");
    }
}

*Note: you should probably rename the activity MainActivity or something equivalent

Answer 2

DialogFragment is a child of Fragment, so it cannot to be cast to Activity.

3 ways to create a dialog.

1. use AlertDialog, which extends Dialog. Actually it is a Window.
2. use DialogFragment, which extends Fragment.
3. use a dialog style Activity, as the document says.

Showing an activity as a dialog on large screens

Instead of showing a dialog as a fullscreen UI when on small screens, you can accomplish the same result by showing an Activity as a dialog when on large screens. Which approach you choose depends on your app design, but showing an activity as a dialog is often useful when your app is already designed for small screens and you'd like to improve the experience on tablets by showing a short-lived activity as a dialog.

To show an activity as a dialog only when on large screens, apply the Theme.Holo.DialogWhenLarge theme to the manifest element:

<activity android:theme="@android:style/Theme.Holo.DialogWhenLarge" >

This one need definition in manifest.