Java NullPointerException 与 android.support.v7.widget.Toolbar
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NullPointerException with android.support.v7.widget.Toolbar
提问by hwg
I am currently trying to implement a navigation drawer in my app. I am having an issue with the Toolbar being null. I have done many searches online and tried many different solutions to no avail. I have not finished writing all the code but I can't launch my app to check the navigation drawer. Can anyone see where I went wrong?
我目前正在尝试在我的应用程序中实现导航抽屉。我遇到了工具栏为空的问题。我在网上做了很多搜索，并尝试了许多不同的解决方案，但无济于事。我还没有写完所有的代码，但我无法启动我的应用程序来检查导航抽屉。谁能看到我哪里出错了？
If there is anything else I need to post, let me know.
如果还有什么我需要发布的，请告诉我。
I included this on all my activity screens
我在我所有的活动屏幕上都包含了这个
<include
android:id="@+id/app_bar"
layout="@layout/app_bar"/>
app_bar.xml
app_bar.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.Toolbar
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:minHeight="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="@style/ThemeOverlay.AppCompat.Dark" >
</android.support.v7.widget.Toolbar>
line 72 of MainActivity
MainActivity 的第 72 行
setSupportActionBar(mToolbar);
Main Activity
主要活动
public class Trans_List extends ActionBarActivity {
private Toolbar mToolbar;
private CharSequence mTitle;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_trans_list);
mToolbar = (Toolbar) findViewById(R.id.app_bar);
setSupportActionBar(mToolbar);
getSupportActionBar().setDisplayShowHomeEnabled(true);
NavigationDrawerFragment drawerFragment = (NavigationDrawerFragment)
getSupportFragmentManager().findFragmentById(R.id.left_drawer);
drawerFragment.setUp((DrawerLayout) findViewById(R.id.drawer_layout), mToolbar);
Style.xml
样式文件
<?xml version="1.0" encoding="utf-8"?>
<resources>
<style name="AppBaseTheme" parent="@style/Theme.AppCompat.Light.DarkActionBar" >
<item name="windowActionBar">false</item>
</style>
<style name="Theme.split" parent="AppBaseTheme">
</style>
<style name="dialog_custom" parent="@style/Theme.AppCompat.Dialog">
<item name="@android:listPreferredItemPaddingLeft">20dip</item>
<item name="@android:listPreferredItemPaddingRight">20dip</item>
<item name="@android:listPreferredItemPaddingStart">20dip</item>
<item name="@android:listPreferredItemPaddingEnd">20dip</item>
</style>
</resources>
LogCat
日志猫
01-07 01:14:29.702 4811-4811/com.lee.yuchan.splt E/AndroidRuntime﹕
FATAL EXCEPTION: main
Process: com.lee.yuchan.splt, PID: 4811
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.lee.yuchan.splt/com.lee.yuchan.splt.Trans_List}:
java.lang.NullPointerException: Attempt to invoke virtual method
'java.lang.CharSequence android.support.v7.widget.Toolbar.getTitle()'
on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access0(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.CharSequence
android.support.v7.widget.Toolbar.getTitle()' on a null object
reference
at android.support.v7.internal.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:95)
at android.support.v7.internal.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:88)
at android.support.v7.internal.app.ToolbarActionBar.<init>(ToolbarActionBar.java:84)
at android.support.v7.app.ActionBarActivityDelegateBase.setSupportActionBar(ActionBarActivityDelegateBase.java:175)
at android.support.v7.app.ActionBarActivity.setSupportActionBar(ActionBarActivity.java:92)
at com.lee.yuchan.splt.Trans_List.onCreate(Trans_List.java:72)
at android.app.Activity.performCreate(Activity.java:5933)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
????????????at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
????????????at android.app.ActivityThread.access0(ActivityThread.java:144)
????????????at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
????????????at android.os.Handler.dispatchMessage(Handler.java:102)
????????????at android.os.Looper.loop(Looper.java:135)
????????????at android.app.ActivityThread.main(ActivityThread.java:5221)
????????????at java.lang.reflect.Method.invoke(Native Method)
????????????at java.lang.reflect.Method.invoke(Method.java:372)
????????????at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
????????????at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Main Activity XML
主要活动 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">
<!-- The main content view -->
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<include
layout="@layout/app_bar"/>
<TextView
android:id="@+id/selectItems"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/select_instr1"
android:textSize="20sp"
android:gravity="center"
android:paddingTop="4sp"
android:paddingBottom="10sp" >
</TextView>
<ListView
android:id="@+id/listView1"
android:layout_width="match_parent"
android:layout_height="0dip"
android:layout_weight="1" >
</ListView>
<Button
android:id="@+id/buttonChecked"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="0dip"
android:background="@drawable/custom_button"
android:textColor="#ffffff"
android:text="@string/next_button" />
</LinearLayout>
<!-- The navigation drawer -->
<fragment
android:id="@+id/left_drawer"
android:layout_width="@dimen/nav_dr"
android:layout_height="match_parent"
android:layout_gravity="start"
app:layout="@layout/fragment_navigation_drawer"
android:name="com.lee.yuchan.splt.NavigationDrawerFragment"
tools:layout="@layout/fragment_navigation_drawer" />
</android.support.v4.widget.DrawerLayout>
采纳答案by hwg
I solved the issue with the toolbar. I realized after hours of searching the web and trying different things, I realized that my code wasn't wrong, it was using layouts from the layout-21 not the layout folder since the emulation for Android 5.0. All modification I had made were in the layout folder. I made the changes to the xml files in the layout-21 folder and the problem was solved. Sorry for the wasted time and post.
我用工具栏解决了这个问题。经过数小时的网络搜索和尝试不同的事情后，我意识到我的代码没有错，它使用的是 layout-21 中的布局，而不是自 Android 5.0 仿真以来的布局文件夹。我所做的所有修改都在布局文件夹中。我对layout-21文件夹中的xml文件进行了修改，问题解决了。抱歉浪费了时间和帖子。
回答by Steve
Set the idattribute in the Toolbarxml like this:
id在Toolbarxml 中设置属性，如下所示：
<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.Toolbar
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/app_bar"
app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:minHeight="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="@style/ThemeOverlay.AppCompat.Dark" >
</android.support.v7.widget.Toolbar>
Then remove it from the includeblock so it looks like this:
然后将其从include块中删除，使其看起来像这样：
<include
layout="@layout/app_bar"/>
And to simplify further you could just remove the includeblock completely and simply insert the Toolbardirectly into the xml where the includewas.
为了进一步简化，您可以完全删除include块，然后将Toolbar直接插入到 xml 所在的include位置。
回答by Raissa Regis
When I had this problem, I configured the layout of the activity and of the toolbar with the same id's
当我遇到这个问题时，我用相同的 id 配置了活动和工具栏的布局
回答by Mahesh V N
<include
android:id="@+id/toolbar"
layout="@layout/tool_bar"/>
android.support.v7.widget.Toolbar.getTitle() on a null object reference happens due to title clashes between ids of and that of the id in toolbar.xml definition . To overcome this issue remove the id in as below and latest Lollipop material design shall work fine with toolbar
android.support.v7.widget.Toolbar.getTitle() 对空对象引用的发生是由于 toolbar.xml 定义中的 id 和 id 之间的标题冲突。为了解决这个问题，删除下面的 id，最新的 Lollipop 材料设计应该可以很好地与工具栏配合使用
<include
layout="@layout/tool_bar"/>
回答by Sash_KP
In my case , i was trying to access the Toolbarinside onAttach()method of a fragment instead of onActivityCreated(), resulting in NullPointerException.
就我而言，我试图访问片段的Toolbar内部onAttach()方法而不是onActivityCreated()，导致NullPointerException.
回答by Mightian
i was struck with the same issue and none of the answer's worked for me, i had actually forgotten to include the toolbar layout in the activity.
我对同样的问题感到震惊，但没有一个答案对我有用，我实际上忘记在活动中包含工具栏布局。
<include layout="@layout/toolbar"/>
回答by bkane56
Answer is a little late but I just ran into this problem.
回答有点晚了，但我刚刚遇到了这个问题。
I had a similar issue and spent 7 hrs messing with it. It worked on 3 of 4 activities just fine but one would crash.
我有一个类似的问题，并花了 7 小时搞乱它。它在 4 个活动中的 3 个上工作得很好，但一个会崩溃。
The only thing that worked for me, and I am not sure why, was to put the:
唯一对我有用的，我不知道为什么，是把：
mToolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(mToolbar);
getSupportActionBar().setDisplayShowHomeEnabled(true);
as the last code in my onCreate. It works perfectly now.
作为我的 onCreate 中的最后一个代码。它现在完美地工作。
回答by Rashed Zzaman
check both line call is ok or not
检查两条线路通话是否正常
setContentView(R.layout.layout_file)
toolbar = (Toolbar) findViewById(R.id.toolbar_top)
回答by Cletus Ajibade
In my own case, i had used
在我自己的情况下，我用过
@Bind(R.id.toolbar)
protected Toolbar toolbar;
at the top of my code but forgot to do
在我的代码顶部但忘了做
ButterKnife.bind(this);
inside onCreate()method
内部onCreate()方法
I hope that helps someone
我希望能帮助某人
Remember to add
记得添加
compile 'com.jakewharton:butterknife:7.0.1'
to your build.gradledependencies and import
到您的build.gradle依赖项并导入
import butterknife.Bind;
import butterknife.ButterKnife;
in your java code and rebuild your app.
在您的 Java 代码中并重建您的应用程序。
回答by nonybrighto
Another possible cause is using a wrong layout in setContentView(R.layout.yourLayout)
另一个可能的原因是在 setContentView(R.layout.yourLayout)
