How to change a theme in Android Studio from NoActionBar to ActionBar-CodePudding

I started a project in Android Studio and apparently the Theme was Theme.NameOfProject.NoActionBar.

This is causing a the following error :

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.weoutdoor/com.example.weoutdoor.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.appcompat.app.ActionBar.setTitle(java.lang.CharSequence)' on a null object reference

The project themes.xml :

<resources xmlns:tools="http://schemas.android.com/tools">
<!-- Base application theme. -->
<style name="Theme.WeOutdoor" parent="Theme.MaterialComponents.DayNight.DarkActionBar">
    <!-- Primary brand color. -->
    <item name="colorPrimary">@color/purple_500</item>
    <item name="colorPrimaryVariant">@color/purple_700</item>
    <item name="colorOnPrimary">@color/white</item>
    <!-- Secondary brand color. -->
    <item name="colorSecondary">@color/teal_200</item>
    <item name="colorSecondaryVariant">@color/teal_700</item>
    <item name="colorOnSecondary">@color/black</item>
    <!-- Status bar color. -->
    <item name="android:statusBarColor" tools:targetApi="l">?attr/colorPrimaryVariant</item>
    <!-- Customize your theme here. -->
</style>

<style name="Theme.WeOutdoor.NoActionBar">
    <item name="windowActionBar">true</item>
    <item name="windowNoTitle">true</item>
</style>

<style name="Theme.WeOutdoor.AppBarOverlay" parent="ThemeOverlay.AppCompat.Dark.ActionBar" />

<style name="Theme.WeOutdoor.PopupOverlay" parent="ThemeOverlay.AppCompat.Light" />

And the AndroidManifest.xml :

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
package="com.example.weoutdoor">

<application
    android:allowBackup="true"
    android:dataExtractionRules="@xml/data_extraction_rules"
    android:fullBackupContent="@xml/backup_rules"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/Theme.WeOutdoor.AppBarOverlay"
    tools:targetApi="31">
    <activity
        android:name=".RegisterActivity"
        android:exported="false" />
    <activity
        android:name=".MainActivity"
        android:exported="true"
        android:theme="@style/Theme.WeOutdoor.NoActionBar">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

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

    </activity>
    <activity android:name=".UserProfileActivity"
        android:exported="true"
        android:theme="@style/Theme.WeOutdoor.AppBarOverlay">

    </activity>
    <activity android:name=".LoginActivity"
        android:exported="true"
        android:theme="@style/Theme.WeOutdoor.AppBarOverlay">

    </activity>

</application>

I tried to change style parent and theme to : ThemeOverlay.AppCompat.Dark.ActionBar

but every time i try to use the code getSupportActionBar().setTitle("WeOutdoor");

i get the mentioned error above.

CodePudding user response：

You're trying to use a ThemeOverlay, which isn't the same as a full Theme. But, honestly, just stick with the NoActionBar theme and create your own toolbar at the top. It's just a layout containing a TextView for the title and some ImageButtons for icons.

CodePudding user response：

This problem might be caused by your theme. Check it again, and make sure that it parents with the Theme.AppCompat.Light.DarkActionBar.

<style name="MyTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <item name="android:windowNoTitle">true</item>
    <item name="windowActionBar">true</item>
    ...
</style>

If your activity extends AppCompatActivity or ActionBarActivity, call getSupportActionBar().

I had the null pointer issue using getSupportActionBar(). My issue was fixed by adding <item name="windowActionBar">true</item> in my styles.xml