java - android.support.design.widget.CollapsingToolbarLayout.setTitle - null 对象引用

Question

我正在做一个 android 项目，我试图在 Activity 中添加自定义工具栏。但是出现以下错误。请帮忙。在 StoryActivity.Java 文件中

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_story);

    CollapsingToolbarLayout collapsingToolbar =
            (CollapsingToolbarLayout) findViewById(R.id.collapsing_toolbar);
    collapsingToolbar.setTitle("Title");
 }

在 Activity_story.xml 中

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
  xmlns:ads="http://schemas.android.com/apk/res-auto"
  android:id="@+id/content_content"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:paddingBottom="@dimen/activity_vertical_margin"
  android:paddingLeft="@dimen/activity_horizontal_margin"
  android:paddingRight="@dimen/activity_horizontal_margin"
  android:paddingTop="@dimen/activity_vertical_margin"
  app:layout_behavior="@string/appbar_scrolling_view_behavior"
  tools:context="com.kidsstorytime.StoryActivity"
  tools:showIn="@layout/app_bar_content">

        <ImageView
            android:layout_width="match_parent"
            android:layout_height="150dp"
            android:id="@+id/contentImageView"
            android:layout_alignParentTop="true"
            android:layout_alignParentLeft="true"
            android:layout_alignParentStart="true"
            android:scaleType="fitXY"
            android:background="@color/colorAccent" />
</RelativeLayout>

在app_bar_story.xml中

<?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.kidsstorytime.MainActivity">
<android.support.design.widget.AppBarLayout android:layout_width="match_parent"
android:layout_height="wrap_content"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:fitsSystemWindows="true"
android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
xmlns:android="http://schemas.android.com/apk/res/android">
    <android.support.design.widget.CollapsingToolbarLayout
        android:id="@+id/collapsing_toolbar"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fitsSystemWindows="true"
        app:contentScrim="?attr/colorPrimary"
        app:expandedTitleMarginEnd="64dp"
        app:expandedTitleMarginStart="48dp"
        app:layout_scrollFlags="scroll|exitUntilCollapsed">

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        app:layout_scrollFlags="scroll|enterAlways"></android.support.v7.widget.Toolbar>

    </android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>

<include layout="@layout/activity_story" />

在AndroidManifest.xml中

 <activity
        android:name=".StoryActivity"
        android:label="@string/title_activity_story"
        android:parentActivityName=".MainActivity"
        android:theme="@style/AppTheme.NoActionBar">
        <meta-data
            android:name="android.support.PARENT_ACTIVITY"

Logcat 错误:

E/AndroidRuntime: FATAL EXCEPTION: main
              Process: com.kidsstorytime, PID: 5633
              java.lang.RuntimeException: Unable to start activity ComponentInfo{com.kidsstorytime/com.kidsstorytime.StoryActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.CollapsingToolbarLayout.setTitle(java.lang.CharSequence)' on a null object reference
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
                  at android.app.ActivityThread.-wrap12(ActivityThread.java)
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
                  at android.os.Handler.dispatchMessage(Handler.java:102)
                  at android.os.Looper.loop(Looper.java:154)
                  at android.app.ActivityThread.main(ActivityThread.java:6077)
                  at java.lang.reflect.Method.invoke(Native Method)
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
               Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.design.widget.CollapsingToolbarLayout.setTitle(java.lang.CharSequence)' on a null object reference
                  at com.beeblebroxlabs.kidsstorytime.StoryActivity.onCreate(StoryActivity.java:30)
                  at android.app.Activity.performCreate(Activity.java:6662)
                  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
                  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)
                  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707) 
                  at android.app.ActivityThread.-wrap12(ActivityThread.java) 
                  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460) 
                  at android.os.Handler.dispatchMessage(Handler.java:102) 
                  at android.os.Looper.loop(Looper.java:154) 
                  at android.app.ActivityThread.main(ActivityThread.java:6077) 
                  at java.lang.reflect.Method.invoke(Native Method) 
                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865) 
                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755) 
            android:value="com.kidsstorytime.MainActivity" />

Answer 1

您正在平展不同的文件

tools:showIn="@layout/app_bar_content">

用这个

tools:showIn="@layout/app_bar_story">

并删除<include layout="@layout/activity_story" /> 来自app_bar_story