大家好，我现在已经面对这个问题几天了。我用google搜索和stackoverflowed但没有人有这个问题的精确解决方案。
是android材料设计的初学者。我试图为我的应用创建一个工具栏，但是一旦使用setSupportActionBar(Toolbar toolbar)，应用程序崩溃，当我摆脱setSupportActionBar(Toolbar toolbar)应用程序运行并且不会崩溃时
这是我的代码..
的build.gradle（模块：APP）
`apply plugin: 'com.android.application'
android {
compileSdkVersion 22
buildToolsVersion "23.0.0 rc3"
defaultConfig {
applicationId "com.example.benson.bestqsystems"
minSdkVersion 9
targetSdkVersion 22
versionCode 1
versionName "1.0"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
}
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
compile 'com.android.support:appcompat-v7:22.2.1'
}
`
styles.xml
`<resources>
<!-- Base application theme. -->
<style name="AppTheme" parent="AppTheme.Base">
<!-- Customize your theme here. -->
</style>
<style name="AppTheme.Base" parent="Theme.AppCompat.NoActionBar">
<item name="colorPrimary">@color/colorPrimary</item>
<item name="colorPrimaryDark">@color/colorPrimaryDark</item>
<item name="colorAccent">@color/colorAccent</item>
</style>
</resources>
`
v21的style.xml
`<?xml version="1.0" encoding="utf-8"?>
<resources>
<style name="AppTheme" parent="AppTheme.Base">
<item name="android:colorPrimary">@color/colorPrimary</item>
<item name="android:colorPrimaryDark">@color/colorPrimaryDark</item>
<item name="android:colorAccent">@color/colorAccent</item>
</style>
</resources>
`
my_app_bar.xml（包含工具栏的布局）
`<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.Toolbar
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:minHeight="?attr/actionBarSize"
android:background="?attr/colorPrimary"
android:id="@+id/app_bar"
xmlns:android="http://schemas.android.com/apk/res/android">
</android.support.v7.widget.Toolbar>`
main_activity布局：
`<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<include layout="@layout/my_app_bar"
/>
<TextView
android:id="@+id/textView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center_horizontal"
android:padding="10dp"
android:text="Large Text"
android:textAppearance="?android:attr/textAppearanceLarge"
android:textSize="35sp" />
<Button
android:id="@+id/testing"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:text="move to second acitivity" />
</LinearLayout>
`
MainActivity.java：
`package com.example.benson.bestqsystems;
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import java.security.MessageDigestSpi;
public class MainAcitvity extends AppCompatActivity implements View.OnClickListener{
private Button move;
private Toolbar toolbar;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_acitvity);
move = (Button) findViewById(R.id.testing);
move.setOnClickListener(this);
setSupportActionBar(toolbar);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main_acitvity, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public void onClick(View v) {
switch(v.getId()){
case R.id.testing:
Message.message(this, "testing please");
startActivity(new Intent(this, Second.class));
break;
}
}
}
`
的AndroidManifest.xml
`<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.benson.bestqsystems" >
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainAcitvity"
android:label="@string/title_activity_main_acitvity" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".Second"
android:label="@string/title_activity_second" >
</activity>
</application>
</manifest>
`
运行我的应用程序后，这是我的logcat
`java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.benson.bestqsystems/com.example.benson.bestqsystems.MainAcitvity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
at android.app.ActivityThread.access$600(ActivityThread.java:123)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4424)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:825)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:592)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at android.support.v7.internal.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:94)
at android.support.v7.internal.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:87)
at android.support.v7.internal.app.ToolbarActionBar.<init>(ToolbarActionBar.java:77)
at android.support.v7.app.AppCompatDelegateImplV7.setSupportActionBar(AppCompatDelegateImplV7.java:198)
at android.support.v7.app.AppCompatActivity.setSupportActionBar(AppCompatActivity.java:96)
at com.example.benson.bestqsystems.MainAcitvity.onCreate(MainAcitvity.java:24)
at android.app.Activity.performCreate(Activity.java:4465)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1051)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
at android.app.ActivityThread.access$600(ActivityThread.java:123)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4424)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:825)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:592)
at dalvik.system.NativeStart.main(Native Method)`
任何人都可以提供帮助，我将非常感激。
答案 0 :(得分：1)
因为你在使用它之前没有初始化toolbar，你只需要添加它。
toolbar = (Toolbar) findViewById(R.id.my_app_bar);
之前：
setSupportActionBar(toolbar);