通过AppCompat获取NullPointerException [英] Getting a NullPointerException with AppCompat
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问题描述
我正在尝试使用AppCompat v21在5.0之前的版本中实现材料设计"，但是当我尝试使用新的工具栏"时却遇到了空指针异常.我按照本指南实施了 http://android-developers.blogspot.com.es/2014/10/appcompat-v21-material-design-for-pre.html .但是我找不到导致NPE的错误.
I'm trying to implements 'Material design' for pre-5.0 using AppCompat v21, but I'm getting a null pointer exception when i try to put on the new 'toolbar'. I followed this guide to implement it http://android-developers.blogspot.com.es/2014/10/appcompat-v21-material-design-for-pre.html. But i cant find the error that causes the NPE.
app.gradle
app.gradle
apply plugin: 'com.android.application'
android {
compileSdkVersion 21
buildToolsVersion "21.1.2"
defaultConfig {
applicationId "com.example.alejandrohall.myapplication"
minSdkVersion 14
targetSdkVersion 21
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-v7:21.0.3'
}
toolbar.xml
toolbar.xml
<android.support.v7.widget.Toolbar xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/my_awesome_toolbar"
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:background="?attr/colorPrimary"/>
styles.xml
styles.xml
<resources>
<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
<!-- Customize your theme here. -->
<item name="colorPrimary">@color/material_blue_grey_950</item>
<item name="windowActionModeOverlay">true</item>
</style>
</resources>
activity_mail.xml
activity_mail.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" tools:context=".MainActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="HOLA MUNDO"
android:id="@+id/textView"
android:layout_centerVertical="true"
android:layout_centerHorizontal="true" />
</RelativeLayout>
MainActivity.java 包com.example.alejandrohall.myapplication;
MainActivity.java package com.example.alejandrohall.myapplication;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
public class MainActivity extends ActionBarActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.my_awesome_toolbar);
setSupportActionBar(toolbar);
}
}
错误
Process: com.example.alejandrohall.myapplication, PID: 6461
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.alejandrohall.myapplication/com.example.alejandrohall.myapplication.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2198)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2257)
at android.app.ActivityThread.access$800(ActivityThread.java:139)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5086)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at android.support.v7.internal.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:95)
at android.support.v7.internal.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:88)
at android.support.v7.internal.app.ToolbarActionBar.<init>(ToolbarActionBar.java:84)
at android.support.v7.app.ActionBarActivityDelegateBase.setSupportActionBar(ActionBarActivityDelegateBase.java:175)
at android.support.v7.app.ActionBarActivity.setSupportActionBar(ActionBarActivity.java:92)
at com.example.alejandrohall.myapplication.MainActivity.onCreate(MainActivity.java:17)
at android.app.Activity.performCreate(Activity.java:5248)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1110)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2162)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2257)
at android.app.ActivityThread.access$800(ActivityThread.java:139)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5086)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
推荐答案
您的toolbar.xml不包含在您的activity_main.xml中，因此findViewById(R.id.my_awesome_toolbar)返回null-您需要直接将Toolbar包含在的布局中每个活动.
Your toolbar.xml is not included in your activity_main.xml and therefore findViewById(R.id.my_awesome_toolbar) returns null - you need to include the Toolbar directly into the layout of each activity.
这篇关于通过AppCompat获取NullPointerException的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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