Why is the back arrow in the toolbar not shown?

问题

My Problem is about the android toolbar. I want to activate the back arrow, to go back to the main menu. I used the expression getSupportActionButton.setDisplayHomeAsUpEnabled(true). When I tested the app, the arrow was not shown. I couldn't find any solutions to solve my problem. When I used the getSupportActionButton.setDefaultDisplayHomeAsUpEnabled(true)-expression, I got the error

ActionBar.setDefaultDisplayHomeAsUpEnabled can only be called from within the same library group (groupId=com.android.support)".

package de.julius.antgo2;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;

public class calendar extends AppCompatActivity {

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

        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setTitle(null);
        if(getSupportActionBar() != null){
            getSupportActionBar().setTitle("Test");
            getSupportActionBar().setDisplayHomeAsUpEnabled(true);
            getSupportActionBar().setDisplayShowHomeEnabled(true);
        }
    }

}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
    android:background="@drawable/apppagebackground"
    android:theme="@style/AppTheme"
    tools:context=".calendar">

    <include
        android:id="@+id/toolbar"
        layout="@layout/toolbar"/>

    <LinearLayout
        android:background="#ffffff"
        android:layout_centerHorizontal="true"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">

        <CalendarView
            android:layout_width="match_parent"
            android:layout_height="match_parent"></CalendarView>

    </LinearLayout>

</RelativeLayout>

回答1:

I thihk the calendar view size is hiding the toolbar or maybe the theme has no action bar

回答2:

Below code is working for me

MainActivity.java

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;

public class MainActivity extends AppCompatActivity {

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

        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        if (getSupportActionBar() != null) {
            getSupportActionBar().setTitle("Test");
            getSupportActionBar().setDisplayHomeAsUpEnabled(true);
            getSupportActionBar().setDisplayShowHomeEnabled(true);
        }
    }


}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorAccent"
    android:theme="@style/AppTheme">

    <include
        android:id="@+id/toolbar"
        layout="@layout/layout_toolbar" />

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/toolbar"
        android:layout_centerHorizontal="true"
        android:background="#ffffff">

        <CalendarView
            android:layout_width="match_parent"
            android:layout_height="match_parent" />

    </LinearLayout>

</RelativeLayout>

styles.xml

<resources>

    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.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>

colors.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <color name="colorPrimary">#008577</color>
    <color name="colorPrimaryDark">#00574B</color>
    <color name="colorAccent">#D81B60</color>
</resources>

layout_toolbar.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.Toolbar xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="?attr/actionBarSize"
    android:background="?attr/colorPrimary"
    android:elevation="4dp" />

Please let me know if not working above code

Below is my output

回答3:

If you are using NoActionBar theme then create a toolbar inside layout file. I am using material component theme of new design support library.

Layout file:

<com.google.android.material.appbar.AppBarLayout
    android:id="@+id/AppBar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:fitsSystemWindows="true"
    android:theme="@style/AppTheme.AppBarOverlay">

    <androidx.appcompat.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        app:layout_scrollFlags="scroll|enterAlways"
        app:popupTheme="@style/AppTheme.PopupOverlay"/>
</com.google.android.material.appbar.AppBarLayout>

Styles:

<style name="AppTheme" parent="Theme.MaterialComponents.Light.DarkActionBar" />
<style name="AppTheme.AppBarOverlay" parent="ThemeOverlay.MaterialComponents.Dark" />
<style name="AppTheme.PopupOverlay" parent="ThemeOverlay.MaterialComponents.Light" />

Java File:

Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
toolbar.setTitle("Title");

if (getSupportActionBar() != null) {
       getSupportActionBar().setHomeButtonEnabled(true);
       getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}

来源：https://stackoverflow.com/questions/57258545/why-is-the-back-arrow-in-the-toolbar-not-shown