Toolbar is not displayed in the editor

Question

Whatever project I design:

The Toolbar is displayed in the emulator but does not appear in the editor.

These errors also appear:

It follows the codes: Styles:

<resources>

<!-- Base application theme. -->
<style name="AppTheme" parent="Base.Theme.AppCompat.Light.DarkActionBar">
    <!-- Customize your theme here. -->
    <item name="colorPrimary">@color/colorPrimary</item>
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="colorAccent">@color/colorAccent</item>
</style>

</resources>

xml:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

Gradle:

apply plugin: 'com.android.application'

android {
compileSdkVersion 28
defaultConfig {
    applicationId "com.example.l.componentes_layout_basicos"
    minSdkVersion 22
    targetSdkVersion 28
    versionCode 1
    versionName "1.0"
    testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}
buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'com.android.support:appcompat-v7:28.0.0-alpha3'
implementation 'com.android.support.constraint:constraint-layout:1.1.2'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.2'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'

}

Answer 1

Colleague you have not implemented the Toolbar, follow how you should do:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

And in the file . java corresponding to this XML screen, put the following:

public class Feedback extends AppCompatActivity {

    private Toolbar toolbar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.tela_feedback);
    //Instanciando, pondo título e adicionando o batão voltar (opcional)
//Lembrando que a partir disso você poderá adicionar mais funcionalidades
        toolbar = findViewById(R.id.toolbar);
        toolbar.setTitle(getResources().getString(R.string.sugestao));
        toolbar.setNavigationIcon(R.drawable.ic_arrow_back);

//Aplicando coor a toolbar
toolbar.setBackgroundColor(getResources().getColor(R.color.unicolor_amareloDark));
            setSupportActionBar(toolbar);
        }

@Override //Método para ativar o botão voltar da toolbar
    public boolean onSupportNavigateUp() {
        onBackPressed();
        return true;
}

    }

In your Style you must change the parent for NoActionBar, as below, so the Actionbar will be hidden:

<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.NoActionBar">
    <!-- Customize your theme here. -->
    <item name="colorPrimary">@color/colorPrimary</item>
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="colorAccent">@color/colorAccent</item>
</style>

</resources>

If there is something else to adjust, comment below