Android actionbar 如何在单个活动中添加带片段的折叠工具栏 这是我的主要活动

这是我的xml文件

错误日志：

FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{}:
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.Toolbar.setNavigationIcon(int)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.Toolbar.setNavigationIcon(int)' on a null object reference
at com.abc.xyz.abcActivity.onCreate(ProjectDetailsActivity.java:32)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
at android.app.ActivityThread.-wrap11(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

活动主题为：

---

只需将这些代码放入片段中，我就可以从片段中访问actionbar

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    View mView = inflater.inflate(R.layout.activity_detail, container, false);

    final Toolbar toolbar = (Toolbar) mView.findViewById(R.id.toolbar);


    AppCompatActivity activity = (AppCompatActivity) getActivity();
    activity.setSupportActionBar(toolbar);
    activity.setTitle("Project Details");
    activity.getSupportActionBar().setDisplayHomeAsUpEnabled(true);

    CollapsingToolbarLayout collapsingToolbar =
            (CollapsingToolbarLayout)mView.findViewById(R.id.collapsing_toolbar);

---

只需将这些代码放入片段中，我就可以从片段中访问actionbar

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    View mView = inflater.inflate(R.layout.activity_detail, container, false);

    final Toolbar toolbar = (Toolbar) mView.findViewById(R.id.toolbar);


    AppCompatActivity activity = (AppCompatActivity) getActivity();
    activity.setSupportActionBar(toolbar);
    activity.setTitle("Project Details");
    activity.getSupportActionBar().setDisplayHomeAsUpEnabled(true);

    CollapsingToolbarLayout collapsingToolbar =
            (CollapsingToolbarLayout)mView.findViewById(R.id.collapsing_toolbar);

---

找到解决办法了。我只需要在片段中获取活动上下文，然后从那里设置工具栏。得到了解决方案。我只需要在片段中获取活动上下文，然后从那里设置工具栏。

FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{}:
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.Toolbar.setNavigationIcon(int)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.Toolbar.setNavigationIcon(int)' on a null object reference
at com.abc.xyz.abcActivity.onCreate(ProjectDetailsActivity.java:32)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
at android.app.ActivityThread.-wrap11(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

@style/Apptheme.Noactionbar

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    View mView = inflater.inflate(R.layout.activity_detail, container, false);

    final Toolbar toolbar = (Toolbar) mView.findViewById(R.id.toolbar);


    AppCompatActivity activity = (AppCompatActivity) getActivity();
    activity.setSupportActionBar(toolbar);
    activity.setTitle("Project Details");
    activity.getSupportActionBar().setDisplayHomeAsUpEnabled(true);

    CollapsingToolbarLayout collapsingToolbar =
            (CollapsingToolbarLayout)mView.findViewById(R.id.collapsing_toolbar);