我正在尝试向我的应用添加后退按钮功能。
但是,当我尝试像这样添加backButton的ID时,
Button back = findViewById(R.id.backButton);
back.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v) {
finish();
}
}
它只是说它的符号缺失。
我正在猜测该按钮的xml引用不存在,可以在哪里添加它。导航栏(后退和主页按钮等)也未显示在android studio应用程序的底部,有没有启用该功能的方法?
答案 0 :(得分:1)
您正在寻找的是BottomNavigationView。
您应该将ID放在onNavigationItemSelected
中。
MainActivty
public class MainActivity extends AppCompatActivity {
private TextView mTextMessage;
private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
= new BottomNavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
switch (item.getItemId()) {
case R.id.navigation_home:
mTextMessage.setText(R.string.title_home);
return true;
case R.id.back:
finish();
return true;
}
return false;
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
BottomNavigationView navView = findViewById(R.id.nav_view);
mTextMessage = findViewById(R.id.message);
navView.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
}
}
activity_main
<?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:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<TextView
android:id="@+id/message"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="@dimen/activity_horizontal_margin"
android:layout_marginLeft="@dimen/activity_horizontal_margin"
android:layout_marginTop="@dimen/activity_vertical_margin"
android:text="@string/title_home"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<android.support.design.widget.BottomNavigationView
android:id="@+id/nav_view"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="0dp"
android:layout_marginEnd="0dp"
android:background="?android:attr/windowBackground"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:menu="@menu/bottom_nav_menu" />
</android.support.constraint.ConstraintLayout>
在菜单文件夹下创建xml文件
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item
android:id="@+id/navigation_home"
android:icon="@drawable/ic_home_black_24dp"
android:title="@string/title_home" />
<item
android:id="@+id/back"
android:icon="@drawable/back"
android:title="@string/title_dashboard" />
</menu>