Android setSupportActionBar()引发空指针异常
我是android新手,我遵循以下材料设计工具栏教程:Android setSupportActionBar()引发空指针异常,android,Android,我是android新手,我遵循以下材料设计工具栏教程: http://www.android4devs.com/2014/12/how-to-make-material-design-app.html 但是在代码实现之后。logcat中显示了以下错误: 04-01 19:16:10.214 2246-2253/com.example.bhaskar.ddit_results E/art﹕ Failed sending reply to debugger: Broken pipe 04-0
http://www.android4devs.com/2014/12/how-to-make-material-design-app.html
但是在代码实现之后。logcat中显示了以下错误:
04-01 19:16:10.214 2246-2253/com.example.bhaskar.ddit_results E/art﹕ Failed sending reply to debugger: Broken pipe
04-01 19:16:11.985 2246-2246/com.example.bhaskar.ddit_results E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.bhaskar.ddit_results, PID: 2246
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.bhaskar.ddit_results/com.example.bhaskar.ddit_results.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:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
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.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.bhaskar.ddit_results.MainActivity.onCreate(MainActivity.java:41)
at android.app.Activity.performCreate(Activity.java:5933)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
我搜索了这个问题,没有找到任何解决方案。希望,有人识别出此错误并对此有一个快速的答案-否则,如果需要,我可以提供更多信息。任何帮助都将得到感谢。在添加任何
视图之前,您需要调用setContentView
,例如工具栏
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main); // <-- call this first
toolbar = (Toolbar) findViewById(R.id.toolbar); // <-- setup views after
setSupportActionBar(toolbar);
setTitle("DDIT_Results");
}
从此,所有菜单项都显示在工具栏中,
通过标准选项菜单回调填充
在添加工具栏之前,您需要从样式中删除操作,如
<style name="AppTheme" parent="Theme.AppCompat.NoActionBar">
<item name="android:windowActionBar">false</item>
<item name="android:windowNoTitle">true</item>
</style>
现在,您可以在“活动”工具栏中看到,请确保在“活动内部清单”中添加主题
<activity
android:name=".MainActivity"
android:label="@string/app_name"
android:theme="@style/AppTheme.NoActionBar" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
然后在style.xml中为上面使用的主题定义此属性
<style name="AppTheme.NoActionBar">
<item name="windowActionBar">false</item>
<item name="windowNoTitle">true</item>
</style>
假的
真的
只需导入
android.support.v7.widget.Toolbar;
不是
在搜索视图之前,您应该先调用setContentView
。谢谢您的快速回复。它起了作用,帮助很大。:)很明显,很简单,但这是一个疏忽。救了我一天。
<android.support.v7.widget.Toolbar
android:id=”@+id/my_awesome_toolbar”
android:layout_height=”wrap_content”
android:layout_width=”match_parent”
android:minHeight=”?attr/actionBarSize”
android:background=”?attr/colorPrimary” />
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.blah);
final Toolbar toolbar = (Toolbar) findViewById(R.id.my_awesome_toolbar);
setSupportActionBar(toolbar);
}
<style name="AppTheme" parent="Theme.AppCompat.NoActionBar">
<item name="android:windowActionBar">false</item>
<item name="android:windowNoTitle">true</item>
</style>
<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.Toolbar xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/appbar"
android:theme="@style/AppTheme"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="?attr/colorPrimary"
android:minHeight="?attr/actionBarSize" />
<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">
<include
android:id="@+id/tool_bar"
layout="@xml/toolbar" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/hello_world" />
</RelativeLayout>
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar actionbar = (Toolbar) findViewById(R.id.tool_bar);
setSupportActionBar(actionbar);
}
}
<activity
android:name=".MainActivity"
android:label="@string/app_name"
android:theme="@style/AppTheme.NoActionBar" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<style name="AppTheme.NoActionBar">
<item name="windowActionBar">false</item>
<item name="windowNoTitle">true</item>
</style>
android.support.v7.widget.Toolbar;
android.widget.Toolbar;