Java ActionBarActivity getSupportActionBar().hide() 抛出 NullPointerException
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ActionBarActivity getSupportActionBar().hide() throws NullPointerException
提问by Abi-
Call
称呼
if (getSupportActionBar() != null)
getSupportActionBar().hide();
or just:
要不就：
getActionBar()
in android.support.v7.app.ActionBarActivity I get such exception:
在 android.support.v7.app.ActionBarActivity 我得到这样的异常：
...
java.lang.NullPointerException
at android.support.v7.app.ActionBarImplICS.hide(ActionBarImplICS.java:302)
at android.support.v7.app.ActionBarImplJB.hide(ActionBarImplJB.java:20)
...
EDIT:it just happens when activity have Theme:
编辑：它只是在活动有主题时发生：
<style name="MyTheme" parent="Theme.AppCompat.Light">
<item name="android:windowNoTitle">true</item>
<item name="android:windowFullscreen">false</item>
</style>
note:
笔记：
getSupportActionBar()
do not return null
不返回空
回答by gunar
Having Theme.AppCompat.Lightboth for pre-ICS and post-ICS will definitely cause issues. The way of doing this is to set a MyThemein:
在Theme.AppCompat.LightICS 之前和 ICS之后同时使用肯定会导致问题。这样做的方法是设置一个MyTheme：
values/styles.xml. This will extend fromTheme.AppCompat.Light. Ex:<style name="MyTheme" parent="Theme.AppCompat.Light">values-v11/styles.xml. This will extend from aHolotheme. Ex:<style name="MyTheme" parent="android:Theme.Holo.Light">
values/styles.xml. 这将从Theme.AppCompat.Light. 前任：<style name="MyTheme" parent="Theme.AppCompat.Light">values-v11/styles.xml. 这将从一个Holo主题延伸。前任：<style name="MyTheme" parent="android:Theme.Holo.Light">
In this way, Android knows what kind of theme to load based on runtime device host API.
这样，Android 就知道要根据运行时设备主机 API 加载什么样的主题。
Don't call getActionBar()once you extend from ActionBarActivity. On post-ICS devices this will run, but for lower API devices you will get a runtime not supported methodException or something equivalent.
不要打电话getActionBar()，一旦你从延伸ActionBarActivity。在后 ICS 设备上，这将运行，但对于较低的 API 设备，您将获得运行时not supported method异常或类似的东西。
回答by Abi-
As I understand
我认为
if (getSupportActionBar() != null)
getSupportActionBar().hide();
is no correct!
Becouse getSupportActionBar()return not-null instance of
(android.support.v7.app.ActionBarImplICS)
不正确！因为getSupportActionBar()返回（android.support.v7.app.ActionBarImplICS）的非空实例
after that we can call hide function (getSupportActionBar().hide();)
之后我们可以调用隐藏函数( getSupportActionBar().hide();)
but inside this function we will have NullPointerException because variable mActionBarinside
android.support.v7.app.ActionBarImplICS instance == null
http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/4.3_r2.1/android/support/v7/app/ActionBarImplICS.java#302
但是在这个函数里面我们会有 NullPointerException 因为变量mActionBar里面 android.support.v7.app.ActionBarImplICS 实例 == null
http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/ android/4.3_r2.1/android/support/v7/app/ActionBarImplICS.java#302
As I understand inside constructor of android.support.v7.app.ActionBarImplICS
据我了解在 android.support.v7.app.ActionBarImplICS 的构造函数中
mActionBar = activity.getActionBar();
return null, because our Activity does not have ActionBar via Theme
返回 null，因为我们的 Activity 没有通过 Theme 的 ActionBar
<style name="MyTheme" parent="Theme.AppCompat.Light">
<item name="android:windowNoTitle">true</item>
<item name="android:windowFullscreen">false</item>
</style>
回答by ruidge
meet the same problem ,but I use code to set fullscreen and noActionbar below instead of theme in xml:
遇到同样的问题，但我使用代码在下面设置全屏和 noActionbar 而不是 xml 中的主题：
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
getSupportActionBar().hide();
setContentView(R.layout.page_welcome);
initViews();
}
this code runs well before ICS but crashs caused by NullPointException above ICS,After some experiments,I got the solution:delete one line code which set no title as below:
这段代码在ICS之前运行良好，但是由于ICS上面的NullPointException导致崩溃，经过一些实验，我得到了解决方案：删除一行没有设置标题的代码如下：
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
// requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
getSupportActionBar().hide();
setContentView(R.layout.page_welcome);
initViews();
}
Then it works well at all platforms. : )
然后它在所有平台上都能很好地工作。:)
回答by Yar
In short:
<item name="android:windowNoTitle">true</item>may be used with Activityonly, NOT ActionBarActivity
简而言之：
<item name="android:windowNoTitle">true</item>只能用于Activity，不可以ActionBarActivity
On the other hand,getSupportActionBar().hide();may be used with ActionBarActivity
另一方面，getSupportActionBar().hide();可以与ActionBarActivity
