如何将底部导航栏实现到 android 应用程序中？

Question

这是一段 Java 代码。 当我点击BottomNavigationView 中的项目时，Android 应用程序停止，它应该打开一个片段。

public class MainActivity extends AppCompatActivity {

       private BottomNavigationView bottomNavigationView;
       private BottomNavigationView bottomNavigationView;


       @Override
       protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            bottomNavigationView = (BottomNavigationView) findViewById(R.id.bottomNavigationView);

            bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {

                @Override
                public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                    FragmentManager fragmentManager = getSupportFragmentManager();
                    FragmentTransaction transaction = fragmentManager.beginTransaction();

与 if-then 和 if-then-else 语句不同，switch 语句可以有多个可能的执行路径：

            switch (item.getItemId()) {

                case R.id.item0:
                    transaction.replace(R.id.content, new Item0_Fragment()).commit();
                    return true;
                case R.id.item1:
                    transaction.replace(R.id.content, new Item1_Fragment()).commit();
                    return true;
                case R.id.item2:
                    transaction.replace(R.id.content, new Item2_Fragment()).commit();
                    return true;
                case R.id.item3:
                    transaction.replace(R.id.content, new Item3_Fragment()).commit();

                    return true;
            }
            return false;
        }

            });
        }

Answer 1

首先，您确实声明了两次 BottomNavigationView。其次，您没有编写完整的代码，而将可能重要的部分放在一边。但是我确实为此编写了代码。尝试阅读我的代码或只是复制和粘贴。你只需要创建你的片段，如果需要帮助，请告诉我。

MainActivity.java

public class MainActivity extends AppCompatActivity  {

List<Fragment> fragmentList;
MyAdapter myAdapter;
ViewPager viewPager;

BottomNavigationView bottomNavigationView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Log.i(TAG,"onCreate()");

    fragmentList = new ArrayList<>();
    fragmentList.add(new Fragment1());
    fragmentList.add(new Fragment2());

    bottomNavigationView = findViewById(R.id.bottomNavigationView);
    viewPager = findViewById(R.id.viewPagerAppActivity);

    myAdapter = new MyAdapter(getSupportFragmentManager());
    viewPager.setAdapter(myAdapter);
    viewPager.setCurrentItem(0);

    bottomNavigationView.setOnNavigationItemSelectedListener(botNavViewItemSelectedListener());

}

public BottomNavigationView.OnNavigationItemSelectedListener botNavViewItemSelectedListener() {
    return new BottomNavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem item) {

            switch (item.getItemId()) {
                case R.id.itemFragment1:

                    viewPager.setCurrentItem(0);
                    break;

                case R.id.itemFragment2:

                    viewPager.setCurrentItem(1);
                    break;
            }

            return true;
        }
    };
}

public class MyAdapter extends FragmentStatePagerAdapter {

    public MyAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        return fragmentList.get(position);
    }

    @Override
    public int getCount() {
        return fragmentList.size();
    }
}
}

activity_main.xml

<android.support.constraint.ConstraintLayout android:layout_width="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical"
    android:layout_height="match_parent"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <android.support.v4.view.ViewPager
        android:id="@+id/viewPagerAppActivity"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toTopOf="@id/bottomNavigationView"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        android:layout_marginBottom="0dp"
        app:layout_constraintTop_toTopOf="parent"
        android:layout_marginTop="0dp"
        app:layout_constraintVertical_bias="1.0" />

    <android.support.design.widget.BottomNavigationView
        app:menu="@menu/menu_bottom"
        android:id="@+id/bottomNavigationView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:itemBackground="@color/colorPrimary"
        app:itemIconTint="@drawable/bottom_bar_item_selector"
        app:itemTextColor="@drawable/bottom_bar_item_selector"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent" />

</android.support.constraint.ConstraintLayout>

menu_bottom.xml 填充我的导航菜单

<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <item android:id="@+id/itemFragment1" android:title="Frag1" android:enabled="true" app:showAsAction="always|withText" android:icon="@mipmap/ic_launcher"/>
    <item android:id="@+id/itemFragment2" android:title="Frag2" android:enabled="true" app:showAsAction="always|withText" android:icon="@mipmap/ic_launcher"/>


</menu>

Answer 2

*片段点击http://www.truiton.com/2017/01/android-bottom-navigation-bar-example/

*用于活动

以下代码使活动的底部导航（与片段相同）

第 1 步：创建一个 BaseActivity 并将其命名为 BaseActivity

BaseActivity.java

public abstract class BaseActivity extends AppCompatActivity implements 
BottomNavigationView.OnNavigationItemSelectedListener{

protected BottomNavigationView navigationView;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(getContentViewId());

    navigationView = findViewById(R.id.navigation);
    navigationView.setOnNavigationItemSelectedListener(this);
    BottomNavigationViewHelper.disableShiftMode(navigationView);

}

@Override
protected void onStart() {
    super.onStart();
    updateNavigationBarState();
}

@Override
public void onPause() {
    super.onPause();

}

@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
    int itemId = item.getItemId();
    if (itemId == R.id.menuBuilding) {
        startActivity(new Intent(this, ActivityA.class));
    } else if (itemId == R.id.menuChat) {
        startActivity(new Intent(this, ActivityB.class));
    } else if (itemId == R.id.menuProfile) {
        startActivity(new Intent(this, ActivityC.class));
    }
    overridePendingTransition(0, 0);
    finish();
    return true;
}

private void updateNavigationBarState() {
    int actionId = getNavigationMenuItemId();
    selectBottomNavigationBarItem(actionId);
}

void selectBottomNavigationBarItem(int itemId) {
    Menu menu = navigationView.getMenu();
    for (int i = 0, size = menu.size(); i < size; i++) {
        MenuItem item = menu.getItem(i);
        boolean shouldBeChecked = item.getItemId() == itemId;
        if (shouldBeChecked) {
            item.setChecked(true);
            break;
        }
    }
}

abstract int getContentViewId();

abstract int getNavigationMenuItemId();
}

第 2 步： 创建一个子活动并将其命名为 ActivityA 并复制粘贴以下代码

ActivityA.java

public class ActivityA extends BaseActivity implements {

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

}

@Override
int getContentViewId() {
    return R.layout.activity_a_layout;
}

@Override
int getNavigationMenuItemId() {
    return R.id.menuBuilding;
}
}

类似创建ActivityB.java和ActivityC.java。使这两个类类似于ActivityA.java。但不同的是ActivityA.java返回

@Override
  int getNavigationMenuItemId() {
     return R.id.menuBuilding;
 }

和

ActivityB.java 返回

@Override
int getNavigationMenuItemId() {
    return R.id.menuChat;
}

和

ActivityC.java返回`

@Override
int getNavigationMenuItemId() {
    return R.id.menuProfile;
}

同时为两个 java 类创建布局并将 activity_a_layout.xml 代码复制粘贴到 ActivityB.java 和 ActivityC.java 的两个布局中

第 3 步：创建一个名为 activity_a_layout 的布局并复制粘贴以下代码

'activity_a_layout.xml'

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:app="http://schemas.android.com/apk/res-auto"
 >


 <RelativeLayout
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:layout_below="@+id/toolbar"
  android:background="@android:color/white">
  <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Coming soon..."
      android:textSize="19sp"
      android:textStyle="bold"
      android:layout_centerInParent="true"/>
</RelativeLayout>
<include
    android:id="@+id/navigation"
    layout="@layout/bottom_navigation"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true" />

</RelativeLayout>

第四步：

创建一个名为 bottom_navigation 的布局并复制粘贴以下代码

bottom_navigation.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.BottomNavigationView 
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/navigation"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@color/dark_grey"
app:itemIconTint="@drawable/nav_item_menu_selector"
app:itemTextColor="@drawable/nav_item_menu_selector"
app:menu="@menu/bottom_nav_items" />

步骤 5：在 res 中创建一个 menu 文件夹并在 menu 中创建一个名为 bottom_nav_items 的文件并复制粘贴以下代码

bottom_nav_items.xml

 <menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto">
<item
    android:id="@+id/menuChat"
    android:icon="@drawable/ic_chat"
    android:title="Chat" />
<item
    android:id="@+id/menuBuilding"
    android:icon="@drawable/ic_building_white"
    android:title="Company" />
<item
    android:id="@+id/menuProfile"
    android:icon="@drawable/menu_item_profile"
    android:title="Profile"
    app:itemTextColor="@android:color/transparent" />
</menu>

**不要忘记在清单中声明 ActivityA.java,ActivityB.java 和 ActivityC.java

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