java setDisplayHomeasUpEnabled可能会产生空点异常

Question

我试图在工具栏中实现一个向上按钮，以重定向到上一个活动。仪表板上的“向上”按钮已编码。JAVA当我点击向上按钮时，它将显示主页

安卓清单。xml

    <activity 安卓:name="fyp.ui_activities.Dashboard"
        安卓:parentActivityName="fyp.ui_activities.Homepage">
        <meta-data 安卓:name="安卓.support.PARENT_ACTIVITY"
            安卓:value="fyp.ui_activities.Homepage"/>
    </activity>

    

主题。xml，我正在使用NoActionBar

仪表板。xml

<安卓x.drawerlayout.widget.DrawerLayout
xmlns:安卓="http://schemas.安卓.com/apk/res/安卓"
xmlns:app="http://schemas.安卓.com/apk/res-auto"
xmlns:tools="http://schemas.安卓.com/tools"
安卓:layout_width="match_parent"
安卓:layout_height="match_parent"
安卓:id="@+id/drawer_layout"
tools:context=".Dashboard">

<LinearLayout
    安卓:layout_width="match_parent"
    安卓:layout_height="match_parent"
    安卓:orientation="vertical"
    >
    <安卓x.appcompat.widget.Toolbar
        安卓:layout_width="match_parent"
        安卓:layout_height="wrap_content"
        安卓:id="@+id/toolbar"
        app:title="@string/dashboardheader"
        app:titleTextColor="@color/font_Primary">
    </安卓x.appcompat.widget.Toolbar>
</LinearLayout>
</安卓x.drawerlayout.widget.DrawerLayout>

仪表板。爪哇

public class Dashboard extends AppCompatActivity {
DrawerLayout drawerLayout;
ActionBarDrawerToggle actionBarDrawerToggle;

TextView speed,rpm,test;
int i,j;
Random rand = new Random();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_dashboard);
    setUpToolbar();
    print();
    createThread();
}

public void setUpToolbar(){
    drawerLayout = findViewById(R.id.drawer_layout);
    Toolbar toolbar = findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    actionBarDrawerToggle  = new ActionBarDrawerToggle(this,drawerLayout,toolbar,R.string.dashboardheader,R.string.dashboardheader);
}

}

错误

java.lang.IllegalArgumentException: No drawer view found with gravity LEFT