使用findviewbyid android.support.v7.widget.toolbar访问工具栏时的NullP

Question

我使用的是support.v7.widget.Toolbar，它无法通过R.id.xyzname findviewbyid找到工具栏。工具栏和工具栏都返回nil。因此，代码在setSupportActionBar(工具栏)。

当在版本为23的设备中进行测试时，相同的应用程序运行良好；在使用版本为16的设备进行测试时，代码与NullPointer一起崩溃。

这是我的活动

class classActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
int currentApiVersion = Build.VERSION.SDK_INT;
mOpenHelper = new IncidentOpenHelper(getApplicationContext());

setContentView(R.layout.login);
AppBarLayout appBarLayout   = (AppBarLayout) View.inflate(this, R.layout.app_toolbar, null);
// [the above code helped me solve the issue]
android.support.v7.widget.Toolbar toolbars = (android.support.v7.widget.Toolbar) appBarLayout.findViewById(R.id.app_bar_toolbar);

setSupportActionBar(toolbars);

client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();
}
}

这是我的布局.xml

<?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="session_management.LoginActivity">

<include
layout="@layout/app_toolbar"/>
<!--
<android.support.design.widget.AppBarLayout
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:theme="@style/AppTheme.AppBarOverlay">
<android.support.v7.widget.Toolbar
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:id="@+id/app_bar_toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="@style/AppTheme.PopupOverlay" />
</android.support.design.widget.AppBarLayout>
-->
<LinearLayout

</Linear layout>


</android.support.design.widget.CoordinatorLayout>

这是我的依赖

compile fileTree(dir: 'libs', include: ['*.jar'])
testCompile 'junit:junit:4.12'
compile 'com.android.support:multidex:1.0.1'
compile 'com.android.support:appcompat-v7:23.1.1'
compile 'com.android.support:design:23.1.1'
compile 'com.google.http-client:google-http-client-jackson2:1.20.0'
compile 'com.google.api-client:google-api-client-android:1.20.0'
compile 'com.google.code.gson:gson:2.4'
compile project('libraries:volley')
/*                                                                                                                                                                                                                                                                                                                                                                        androidTestCompile 'com.android.support.test.uiautomator:uiautomator-v18:2.1.1'
                                                                                                                                                                                                                                                                                                          */
compile 'com.google.android.gms:play-services-appindexing:8.4.0'
compile project(':cloudendpoint')

}

这是我的app_toolbar.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.AppBarLayout android:layout_height="wrap_content"
android:layout_width="match_parent"
android:theme="@style/AppTheme.AppBarOverlay"
xmlns:android="http://schemas.android.com/apk/res/android">
<android.support.v7.widget.Toolbar
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:id="@+id/app_bar_toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="@style/AppTheme.PopupOverlay" />
</android.support.design.widget.AppBarLayout>

Answer 1

使用v7支持工具栏来支持较低的设备。像这个

android.support.v7.widget.Toolbar toolbar = (android.support.v7.widget.Toolbar) findViewById(R.id.app_bar_toolbar);