java - setSupportActionBar(工具栏工具栏) 在我的 Material 项目中不起作用

Question

大家好，我已经面临这个问题几天了。我已经用谷歌搜索和 stackoverflowed 但没有人对这个问题有精确的解决方案。

我是 Android Material 设计的初学者。我正在尝试为我的应用程序创建一个工具栏，但是一旦使用setSupportActionBar(Toolbar工具栏)，当我摆脱setSupportActionBar(Toolbar Toolbar)应用程序时，应用程序崩溃运行并且不会崩溃

这是我的代码..

build.gradle(模块:应用程序)

`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'
}
`

样式.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(包含我的工具栏的布局)

`<?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;
        }
    }
}
`

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。

Answer 1

这是因为你在使用之前没有初始化toolbar，你只需添加这个即可。

toolbar = (工具栏) findViewById(R.id.my_app_bar);

在此之前:

setSupportActionBar(工具栏);