如何使用此方法getActionBar（）。setDisplayHomeAsUpEnabled（true）;

-4

我得到錯誤：如何使用此方法getActionBar（）。setDisplayHomeAsUpEnabled（true）;

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_peripheral); 
    getActionBar().setDisplayHomeAsUpEnabled(true);//on this line i am getting error 
    mListViewHeader = (View) getLayoutInflater().inflate(R.layout.peripheral_list_services_header, null, false); 

    connectViewsVariables(); 

    final Intent intent = getIntent(); 
    mDeviceName = intent.getStringExtra(EXTRAS_DEVICE_NAME); 
    mDeviceAddress = intent.getStringExtra(EXTRAS_DEVICE_ADDRESS); 
    mDeviceRSSI = intent.getIntExtra(EXTRAS_DEVICE_RSSI, 0) + " db"; 
    mDeviceNameView.setText(mDeviceName); 
    mDeviceAddressView.setText(mDeviceAddress); 
    mDeviceRssiView.setText(mDeviceRSSI); 
    getActionBar().setTitle(mDeviceName); 

    // mListView.addHeaderView(mListViewHeader); 
// mListView.setOnItemClickListener(listClickListener); 
}

的logcat：

time: Shutting down VM 
06-27 11:52:11.363 31628-31628/com.example.android.bleiqn E/AndroidRuntime: FATAL EXCEPTION: main 
    Process: com.example.android.bleiqn, PID: 31628 
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.bleiqn/com.example.android.bleiqn.PeripheralActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2423) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2483) 
     at android.app.ActivityThread.access$900(ActivityThread.java:153) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1349) 
     at android.os.Handler.dispatchMessage(Handler.java:102) 
     at android.os.Looper.loop(Looper.java:148) 
     at android.app.ActivityThread.main(ActivityThread.java:5441) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628) 
    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference 
     at com.example.android.bleiqn.PeripheralActivity.onCreate(PeripheralActivity.java:32) 
     at android.app.Activity.performCreate(Activity.java:6303) 
     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1108) 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2376) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2483)  
     at android.app.ActivityThread.access$900(ActivityThread.java:153)  
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1349)  
     at android.os.Handler.dispatchMessage(Handler.java:102)  
     at android.os.Looper.loop(Looper.java:148)  
     at android.app.ActivityThread.main(ActivityThread.java:5441)  
     at java.lang.reflect.Method.invoke(Native Method)  
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738)  
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628)

我該如何解決呢？

來源

2017-06-27 neha

檢查這個https://stackoverflow.com/questions/34278878/如何提供導航與工具欄-v7-工具欄上的主頁按鈕您必須首先設置工具欄。 – amarok

很難從您的活動類中判斷錯誤，它可能發生在您的主題，佈局或操作欄類型中。最好也發佈xml文件。

它看起來像你要調用操作欄而不添加操作欄佈局，這就是爲什麼它給空對象引用。

如果您已將操作欄添加爲工具欄，請從工具欄創建對象並將其設置爲操作欄，如setSupportActionBar（toolbar）;

希望這會有所幫助。

來源

2017-06-27 06:52:22 KZoNE

添加工具欄在XML文件中：

<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"> 

<android.support.design.widget.AppBarLayout 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:theme="@style/AppTheme.AppBarOverlay"> 

    <android.support.v7.widget.Toolbar 
     android:id="@+id/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> 

<include layout="@layout/content_capture_and_upload_loan_paper" /> 

<android.support.design.widget.FloatingActionButton 
    android:id="@+id/fab" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_gravity="bottom|end" 
    android:layout_margin="@dimen/fab_margin" 
    android:src="@android:drawable/ic_dialog_email" />

和活動的文件中使用工具欄的ID：

Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
    setSupportActionBar(toolbar);  
    getSupportActionBar().setDefaultDisplayHomeAsUpEnabled(true);

來源

2017-06-27 07:12:32

如何使用此方法getActionBar（）。setDisplayHomeAsUpEnabled（true）;

回答

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