Android底层导航

Question

我已经在我的应用程序中实现了一个底部导航栏，问题是无论我在仪表板图标上的哪个活动都是突出显示的。我如何得到它，因此，无论我在哪个活动是突出显示的？

public class Dashboard extends AppCompatActivity
    implements View.OnClickListener
{

private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
        = new BottomNavigationView.OnNavigationItemSelectedListener()
{
    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item)
    {
        switch (item.getItemId())
        {
            case R.id.navigation_request:
                Intent r = new Intent(Dashboard.this, Request.class);
                startActivity(r);
                finish();
                break;
            case R.id.navigation_settings:
                Intent s = new Intent(Dashboard.this, AppSettings.class);
                startActivity(s);
                finish();
                break;
        }
        return false;
    }
};

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_dashboard);

BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation);
    navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
}

这是我的XML菜单文件

<?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/navigation_request"
    android:icon="@drawable/ic_request_icon"
    android:title="@string/title_request" />

<item
    android:id="@+id/navigation_settings"
    android:icon="@drawable/ic_icon_settings"
    android:title="@string/title_settings" />

</menu>

下面是如何在我的activity_dashboard中使用导航

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">

<FrameLayout
    android:id="@+id/content"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="1">

<!-- ONLY TEXTVIEWS ARE HERE -->

</FrameLayout>



<android.support.design.widget.BottomNavigationView
    android:id="@+id/navigation"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom"
    android:background="?android:attr/windowBackground"
    app:menu="@menu/navigation" />

</LinearLayout>

Answer 1

不建议使用所有重复BottomNavigationView及其相关代码(如OnNavigationItemSelectedListener等)的许多不同的BottomNavigationView实例。相反，当用户与Activity交互时，您通常会使用一个BottomNavigationView和多个Fragment实例，这些实例是.replace()d进入内容区域。

话虽如此，让我们看看能否解决你的问题。

这个谜题有两块。第一个问题很简单:您必须指出您的BottomNavigationView中应该选择哪一项。这可以通过调用setSelectedItemId()来实现。将类似的内容添加到onCreate()方法中。

    navigation.setSelectedItemId(R.id.navigation_settings);

第二个问题则要复杂一些。当您调用setSelectedItemId()时，系统会表现得好像用户已经点击了该项一样。换句话说，您的OnNavigationItemSelectedListener将被触发。

在查看您发布的侦听器时，我注意到您总是return false。如果您检查了onNavigationItemSelected()的文档，您会发现

返回：true以显示所选项，如果不应选择该项，则返回false

因此，如果不将侦听器更改为返回setSelectedItemId()，对true的调用就无法工作。

如果将调用setSelectedItemId()放在您的setOnNavigationItemSelectedListener()调用之前，仍然可以使用调用来解决问题，但这只是掩盖了问题。如果希望点击的项目以选定的形式出现，最好将侦听器修复为返回true。

Answer 2

步骤-1将下面的代码放入应用程序级Build.gradle中

implementation 'androidx.navigation:navigation-fragment:2.3.0'

implementation 'com.google.android.material:material:1.2.1'

implementation 'androidx.navigation:navigation-ui:2.3.0'

步骤2将下面的代码放入activity_main.xml中

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingTop="?attr/actionBarSize">

    <com.google.android.material.bottomnavigation.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" />

    <fragment
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toTopOf="@id/nav_view"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

将下面的代码放入菜单/_nav_menu.xml

<?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/navigation_dashboard"
        android:icon="@drawable/ic_dashboard_black_24dp"
        android:title="Orders" />
    <item
        android:id="@+id/navigation_notifications"
        android:icon="@drawable/ic_notifications_black_24dp"
        android:title="Services" />
    <item
        android:id="@+id/navigation_account"
        android:icon="@drawable/ic_notifications_black_24dp"
        android:title="Account" />
</menu>

步骤-4将下面的代码放入MainActivity.java中

import android.os.Bundle;
import android.view.MenuItem;

import com.example.bottomnavigationdemo.ui.account.AccountFragment;
import com.example.bottomnavigationdemo.ui.dashboard.DashboardFragment;
import com.example.bottomnavigationdemo.ui.home.HomeFragment;
import com.example.bottomnavigationdemo.ui.notifications.NotificationsFragment;
import com.google.android.material.bottomnavigation.BottomNavigationView;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentTransaction;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import androidx.navigation.ui.AppBarConfiguration;
import androidx.navigation.ui.NavigationUI;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        BottomNavigationView navView = findViewById(R.id.nav_view);
        navView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                switch (item.getItemId()) {
                    case R.id.navigation_home:
                        Fragment fragment = new HomeFragment();
                        getSupportFragmentManager().beginTransaction()
                                .replace(R.id.nav_host_fragment, fragment, fragment.getClass().getSimpleName())
                                .commit();
                        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
                        transaction.replace(R.id.nav_host_fragment, fragment, fragment.getClass().getSimpleName());
                        transaction.commit();
                        return true;

                    case R.id.navigation_dashboard:
                        Fragment fragment2 = new DashboardFragment();
                        transaction = getSupportFragmentManager().beginTransaction();
                        transaction.replace(R.id.nav_host_fragment, fragment2, fragment2.getClass().getSimpleName());

                        transaction.commit();
                        return true;

                    case R.id.navigation_notifications:
                        Fragment fragment3 = new NotificationsFragment();
                        transaction = getSupportFragmentManager().beginTransaction();
                        transaction.replace(R.id.nav_host_fragment, fragment3, fragment3.getClass().getSimpleName());
                        transaction.commit();
                        return true;

                    case R.id.navigation_account:
                        Fragment fragment4 = new AccountFragment();
                        transaction = getSupportFragmentManager().beginTransaction();
                        transaction.replace(R.id.nav_host_fragment, fragment4, fragment4.getClass().getSimpleName());
                        transaction.commit();
                        return true;
                }
                return true;
            }

        });
    }

}

步骤-5将下面的代码放入HomeFragment.java中

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;

import com.example.bottomnavigationdemo.R;
import com.example.bottomnavigationdemo.ui.dashboard.DashboardFragment;

public class HomeFragment extends Fragment {

    public View onCreateView(@NonNull LayoutInflater inflater,
                             ViewGroup container, Bundle savedInstanceState) {
        View root = inflater.inflate(R.layout.fragment_home, container, false);
        return root;
    }
}

Answer 3

只需使用方法setSelectedItemId(int id)，让我们将项目标记为选定项，就好像它是被点击的一样。

如下所示：

BottomNavigationView bottomNavigationView;
bottomNavigationView = (BottomNavigationView) 
findViewById(R.id.bottomNavigationView);
bottomNavigationView.setSelectedItemId(R.id.my_menu_item_id);