我試圖在RegisterActivity的Action Bar中添加按鈕,但它將我帶出應用程序而沒有崩潰,並且警告告訴我setDisplayHomeAsUpEnabled可能會產生NullPonterException,我遵循Android Developer控制檯中的指令,並且看到很多類似於我的案例,但冷卻沒有實現我的案件的答案的問題,所以我需要一個來幫助我的案件。 這裏是我的代碼:setDisplayHomeAsUpEnabled產生NullPonterException
RegisterActivity:
public class RegisterActivity extends AppCompatActivity {
private Toolbar mToolbar;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_register);
mToolbar = (Toolbar) findViewById(R.id.register_toolbar);
setSupportActionBar(mToolbar);
getSupportActionBar().setTitle("Creat Account");
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setDisplayShowHomeEnabled(true);
}
}
我試試這個,但也沒有工作:
if (getSupportActionBar() != null) {
getSupportActionBar().setTitle("Creat Account");
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setDisplayShowHomeEnabled(true);
}
activity_register.xml:
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
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"
tools:context="com.mohamed71.lapitchat.RegisterActivity">
<include
android:id="@+id/register_toolbar"
layout="@layout/app_bar_layout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
tools:layout_editor_absoluteX="8dp"
tools:layout_editor_absoluteY="0dp" />
app_bar_layout.xml:
<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.Toolbar
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/main_app_bar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@color/colorPrimary"
android:theme="@style/Base.ThemeOverlay.AppCompat.Dark.ActionBar"
android:minHeight="?attr/actionBarSize"
>
</android.support.v7.widget.Toolbar>
AndriodMainifest.xml:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.mohamed71.lapitchat">
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.INTERNET" />
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".StartActivity" />
<activity
android:name=".RegisterActivity"
android:parentActivityName=".StartActivity" />
</application>
的可能的複製[什麼是空指針異常,以及如何解決?(https://stackoverflow.com/questions/218384/什麼 - 是 - 一 - NullPointerException異常和知識-DO-I-FIX-IT) – Zoe