我编写了一个包含 3 个 Activity 的测验:1 = QuizActivity,2 = Menu2 和 3 = Menu3。 Activity 1 和 2 运行良好。问题出在 Menu3 中。有一行代码正在创建 Nullpoiner excption:void android.support.v7.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference 当我删除此行时,我可以开始(通过单击抽屉导航上的关于项目(导致 Menu3 Activity )) menu3 Activity 。唯一的问题是,当我省略这一行时,“汉堡图标”(您可以在图片上看到)不再存在。当我离开行代码时,我无法导航到 Menu3,因为当我这样做时,应用程序会强制关闭。我该如何解决这个问题?
菜单 3 java:
package amapps.impossiblequiz;
import static amapps.impossiblequiz.R.id.nv3;
public class Menu3 extends AppCompatActivity {
private DrawerLayout mDrawerLayout3;
private ActionBarDrawerToggle mToggle;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_menu3);
Toolbar mToolbar = (Toolbar) findViewById(R.id.nav_action);
setSupportActionBar(mToolbar);
mDrawerLayout3 = (DrawerLayout) findViewById(R.id.drawerLayout3);
mToggle = new ActionBarDrawerToggle(this, mDrawerLayout3, R.string.open, R.string.close);
mDrawerLayout3.addDrawerListener(mToggle);
mToggle.syncState();
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
NavigationView mNavigationView = (NavigationView) findViewById(nv3);
mNavigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(MenuItem menuItem){
switch (menuItem.getItemId()){
case(R.id.nav_home3):
Intent accountActivity3 = new Intent(getApplicationContext(),QuizActivity.class);
startActivity(accountActivity3);
}
return true;
}
});
}
@Override //Makes that the "Burger" Item, shows the Drawer if someone clicks on the simbol
public boolean onOptionsItemSelected(MenuItem item) {
if (mToggle.onOptionsItemSelected(item)) {
return true;
}
return super.onOptionsItemSelected(item);
}
菜单 3 XML:
<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout
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="amapps.impossiblequiz.Menu3"
android:id="@+id/drawerLayout3">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignParentEnd="true"
android:layout_alignParentRight="true"
android:layout_marginBottom="215dp"
android:layout_marginEnd="42dp"
android:layout_marginRight="42dp"
android:text="Button" />
</RelativeLayout>
<android.support.design.widget.NavigationView
android:layout_width="wrap_content"
android:layout_height="match_parent"
app:menu="@menu/navigation_menu3"
android:layout_gravity="start"
android:id="@+id/nv3"
app:headerLayout="@layout/navigation_header"
app:itemIconTint="@drawable/tint_color_selector2">
</android.support.design.widget.NavigationView>
</android.support.v4.widget.DrawerLayout>
菜单 2 XML:
<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout
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="amapps.impossiblequiz.Menu2"
android:id="@+id/drawerLayout2"
android:orientation="vertical">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<include
layout="@layout/navigation_action"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<RelativeLayout
android:layout_width="wrap_content"
android:layout_height="match_parent">
<TextView
android:id="@+id/textScore2"
android:layout_width="wrap_content"
android:layout_height="50dp"
android:background="#f60"
android:paddingTop="10dp"
android:paddingLeft="35dp"
android:text="Your score is:"
android:textAppearance="@style/TextAppearance.AppCompat"
android:textColor="#ffffff"
android:textSize="20dp"
android:layout_marginTop="28dp"
android:layout_below="@+id/textView2"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
<TextView
android:id="@+id/textHighScore"
android:layout_width="wrap_content"
android:layout_height="50dp"
android:background="#FFAB00"
android:paddingLeft="35dp"
android:paddingRight="100dp"
android:paddingTop="10dp"
android:text="Highest score:"
android:textAppearance="@style/TextAppearance.AppCompat"
android:textColor="#ffffff"
android:textSize="20dp"
android:layout_marginTop="13dp"
android:layout_below="@+id/textScore2"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
<Button
android:id="@+id/tryAgain_button"
android:layout_width="150dp"
android:layout_height="50dp"
android:background="@drawable/bg_pill"
android:onClick="onClick"
android:text="Restart Quiz!"
android:textColor="#ffffff"
android:layout_marginTop="18dp"
android:layout_below="@+id/textHighScore"
android:layout_centerHorizontal="true" />
<TextView
android:id="@+id/textView2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="33dp"
android:text="Stats: play and get trophies!"
android:textAppearance="@style/TextAppearance.AppCompat.Button"
android:textSize="20dp"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true" />
<ImageView
android:id="@+id/statsTrophy"
app:srcCompat="@drawable/statsoftrophy"
android:layout_width="50dp"
android:layout_height="50dp"
android:layout_alignTop="@+id/textHighScore"
android:layout_above="@+id/tryAgain_button"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true" />
<ImageView
android:id="@+id/trophy1"
android:layout_width="80dp"
android:layout_height="80dp"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_below="@+id/tryAgain_button"
android:layout_marginLeft="26dp"
android:layout_marginStart="26dp"
android:layout_marginTop="70dp"
android:visibility="invisible"
app:srcCompat="@drawable/trophy1" />
<ImageView
android:id="@+id/trophy2"
android:layout_width="80dp"
android:layout_height="80dp"
android:layout_alignTop="@+id/trophy1"
android:layout_marginLeft="24dp"
android:layout_marginStart="24dp"
android:layout_toEndOf="@+id/trophy1"
android:layout_toRightOf="@+id/trophy1"
android:visibility="invisible"
app:srcCompat="@drawable/trophy2" />
<Button
android:id="@+id/enablePOPUP"
android:layout_width="80dp"
android:layout_height="30dp"
android:text="Info"
android:alpha="0.30"
android:visibility="invisible"
android:background="@drawable/bg_pill_trophy"
android:textColor="#ffffff"
android:layout_alignTop="@+id/enablePOPUP2"
android:layout_alignLeft="@+id/trophy1"
android:layout_alignStart="@+id/trophy1" />
<Button
android:id="@+id/enablePOPUP2"
android:layout_width="60dp"
android:layout_height="30dp"
android:background="@drawable/bg_pill_trophy"
android:text="Info"
android:textColor="#ffffff"
android:alpha="0.30"
android:visibility="invisible"
android:layout_marginTop="12dp"
android:layout_below="@+id/trophy2"
android:layout_alignLeft="@+id/trophy2"
android:layout_alignStart="@+id/trophy2"
android:layout_alignRight="@+id/trophy2"
android:layout_alignEnd="@+id/trophy2" />
<ImageView
android:id="@+id/trophy3"
android:layout_width="80dp"
android:layout_height="80dp"
android:layout_alignTop="@+id/trophy2"
android:layout_toLeftOf="@+id/statsTrophy"
android:layout_toStartOf="@+id/statsTrophy"
app:srcCompat="@drawable/trophy3"
android:visibility="invisible"/>
<Button
android:id="@+id/enablePOPUP3"
android:layout_width="60dp"
android:layout_height="30dp"
android:background="@drawable/bg_pill_trophy"
android:text="Info"
android:textColor="#ffffff"
android:alpha="0.30"
android:visibility="invisible"
android:layout_alignBottom="@+id/enablePOPUP2"
android:layout_alignLeft="@+id/trophy3"
android:layout_alignStart="@+id/trophy3"
android:layout_alignTop="@+id/enablePOPUP2"
android:layout_alignRight="@+id/trophy3"
android:layout_alignEnd="@+id/trophy3" />
</RelativeLayout>
</LinearLayout>
<android.support.design.widget.NavigationView
android:layout_width="wrap_content"
android:layout_height="match_parent"
app:menu="@menu/navigation_menu2"
android:layout_gravity="start"
android:id="@+id/nv2"
app:headerLayout="@layout/navigation_header"
app:itemIconTint="@drawable/tint_color_selector2">
</android.support.design.widget.NavigationView>
最佳答案
尝试更改 toogle 初始化。可能对您有帮助。
mToggle = new ActionBarDrawerToggle(this, mDrawerLayout3, mToolbar, R.string.open, R.string.close);
编辑 1
我解决了你的问题。你打电话时 getSupportActionBar 你会得到你最近设置的 actionBar。所以,这意味着你的工具栏是空的。检查您的工具栏 ID 是否正确。
附言此外,您可以简单地调用
ActionBar actionBar = setSupportActionBar(mToolbar);
因为 setSupportActionBar()
返回 ActionBar
编辑2
您的 xml 文件中没有工具栏。添加它。
关于java - 抽屉导航错误/空指针异常错误,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/45304655/