android studio上的Java错误

我是android应用程序开发新手，我正在关注buckys教程 目前我在这方面 我按指示做了所有事情，但当我运行应用程序时，我发现这个错误，这是我的日志

12-08 20:42:45.548 2465-2465/com.kimdevelopment.kimmmm I/art: Not late-enabling -Xcheck:jni (already on)
12-08 20:42:45.549 2465-2465/com.kimdevelopment.kimmmm I/art: Late-enabling JIT
12-08 20:42:45.552 2465-2465/com.kimdevelopment.kimmmm I/art: JIT created with code_cache_capacity=2MB compile_threshold=1000
12-08 20:42:45.630 2465-2465/com.kimdevelopment.kimmmm W/System: ClassLoader referenced unknown path: /data/app/com.kimdevelopment.kimmmm-1/lib/x86
12-08 20:42:45.696 2465-2465/com.kimdevelopment.kimmmm D/AndroidRuntime: Shutting down VM
12-08 20:42:45.696 2465-2465/com.kimdevelopment.kimmmm E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.kimdevelopment.kimmmm, PID: 2465
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.kimdevelopment.kimmmm/com.kimdevelopment.kimmmm.MainActivity}: 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: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 'java.lang.CharSequence android.support.v7.widget.Toolbar.getTitle()' on a null object reference
    at android.support.v7.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:98)
    at android.support.v7.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:91)
    at android.support.v7.app.ToolbarActionBar.<init>(ToolbarActionBar.java:73)
    at android.support.v7.app.AppCompatDelegateImplV7.setSupportActionBar(AppCompatDelegateImplV7.java:205)
    at android.support.v7.app.AppCompatActivity.setSupportActionBar(AppCompatActivity.java:99)
    at com.kimdevelopment.kimmmm.MainActivity.onCreate(MainActivity.java:27)
    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)
12-08 20:42:54.014 2465-2465/? I/Process: Sending signal. PID: 2465 SIG: 9

最后是xml文件

<?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"
    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.kimdevelopment.kimmmm.MainActivity"
    tools:showIn="@layout/activity_main">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!" />
</RelativeLayout>

---

您的XML中实际上没有引用工具栏的元素。您需要一个ID为“toolbar”的元素，可能如下所示：

<?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"
    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.kimdevelopment.kimmmm.MainActivity"
    tools:showIn="@layout/activity_main">
    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="@color/blue"
        android:foreground="?android:attr/windowContentOverlay"
        app:theme="@style/Toolbar"/>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!" />
</RelativeLayout>

setContentView(R.layout.main_layout);

您应该更改XML main

RelativeLayout

并为其指定一个id（如其中的元素），然后将内容视图设置为：

<?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"
    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.kimdevelopment.kimmmm.MainActivity"
    tools:showIn="@layout/activity_main">
    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="@color/blue"
        android:foreground="?android:attr/windowContentOverlay"
        app:theme="@style/Toolbar"/>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!" />
</RelativeLayout>

setContentView(R.layout.main_layout);

---

我没有太多地使用工具栏，所以我可能会关闭，但您正在使用一个R.id实例化工具栏，该R.id通常对应于一个XML元素。

比添加指向另一个主题的链接更好，这不是我的问题，如果可以的话，您可以提供帮助。这是同样的问题。您需要读取错误，找出什么是null，以及为什么它是null。这就是链接问题中解释的。但我没有添加或删除任何可能导致此问题的内容。我使用的是Noactionbar主题，我也尝试过，但仍然出现错误我编辑了我的回答。。。希望能有帮助。请再解释一下