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[英]getsupportActionBar().setDisplayHomeAsUpEnabled(true).setDisplayHomeAsUpEnabled(true) throws NullPointerException
[英]getSupportActionBar().setDisplayHomeAsUpEnabled(true); throws NullPointerException
首先,我知道這個問題已經問過了,我花了一個小時研究其他解決方案,主要是從-getActionBar()返回null ,並且沒有一個起作用,所以另一雙眼睛也許可以做點什么。
其他類繼承的NavigationDrawer類:
public class NavigationDrawer extends AppCompatActivity {
String[] mDrawerTitles;
DrawerLayout mDrawerLayout;
ListView mDrawerList;
ActionBarDrawerToggle mDrawerToggle;
String activityTitle;
@Override
protected void onCreate(Bundle savedInstanceState) {
this.requestWindowFeature(Window.FEATURE_NO_TITLE);
super.onCreate(savedInstanceState);
setContentView(R.layout.navigation_drawer_layout);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
mDrawerTitles = getResources().getStringArray(R.array.drawer_array);
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
mDrawerList = (ListView) findViewById(R.id.left_drawer);
activityTitle = getTitle().toString();
getSupportActionBar().setDisplayHomeAsUpEnabled(true); //here is where the error is thrown
getSupportActionBar().setHomeButtonEnabled(true);
addDrawerItems();
navDrawerSetup();
}
MainActiviy擴展了以上內容:
public class MainActivity extends NavigationDrawer {
int[]images={R.drawable.user_manual,R.drawable.tips_tricks, R.drawable.troubleshooting};
Integer printer;
ListView myListView;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
LayoutInflater inflater = (LayoutInflater) this.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View contentView = inflater.inflate(R.layout.activity_main, null, false);
mDrawerLayout.addView(contentView, 0);
}
導航抽屜.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:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior">
<FrameLayout
android:id="@+id/content_frame"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<ListView
android:id="@+id/left_drawer"
android:layout_width="240dp"
android:layout_height="match_parent"
android:layout_gravity="start"
android:background="#999"
android:choiceMode="singleChoice"
android:divider="@android:color/transparent"
android:dividerHeight="0dp" />
</android.support.v4.widget.DrawerLayout>
styles.xml
<resources>
<!-- Base application theme. -->
<style name="AppTheme" parent="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>
<style name="AppTheme.NoActionBar">
<item name="windowActionBar">false</item>
<item name="windowNoTitle">true</item>
</style>
<style name="AppTheme.AppBarOverlay" parent="ThemeOverlay.AppCompat.Dark.ActionBar" />
<style name="AppTheme.PopupOverlay" parent="ThemeOverlay.AppCompat.Light" />
</resources>
activity_main
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 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:fitsSystemWindows="true"
tools:context="com.example.shelleyd.myapplication.MainActivity">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme.AppBarOverlay">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="@style/AppTheme.PopupOverlay" />
</android.support.design.widget.AppBarLayout>
content_main
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:id="@+id/content_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context="com.example.shelleyd.myapplication.MainActivity"
tools:showIn="@layout/activity_main">
<ListView
android:id="@+id/myList"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_gravity="center_vertical"
android:layout_weight="1" />
</LinearLayout>
在NavigationDrawer
活動中,您正在執行setContentView(R.layout.navigation_drawer_layout)
,在navigation_drawer_layout
中沒有任何Toolbar
,這會導致異常。
在NavigationDrawer.class中執行以下操作
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); //This is null
setSupportActionBar(toolbar);
您正在將“活動”工具欄設置為null,因為R.layout.activity_main中沒有帶有R.id.toolbar ID的視圖。 因此,當您嘗試在上面的代碼后設置工具欄時,嘗試在null對象中設置一個屬性,該屬性會產生null指針異常。
刪除活動中的上述兩行,或在R.layout.activity_main布局文件上聲明具有R.id.toolbar ID的工具欄視圖。 這樣做將解決問題。
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