Question

我正在使用底部导航栏的项目中工作，但是当我运行该应用程序时，只有点击底部导航栏菜单项中的图标，片段活动才会自动出现。

屏幕截图：

当我点击任何片段活动时，空白活动首先出现，然后出现。

这是我的代码：

BottomNavigation.java

import android.content.DialogInterface;
import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.design.widget.BottomNavigationView;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.MenuItem;
import android.widget.FrameLayout;

public class BottomNavigation extends AppCompatActivity {

    private BottomNavigationView mMianNav;
    private FrameLayout mMainFrame;
    private AllResturant allResturant;
    private UserProfile userprofile;
    private ActivityUser activityUser;

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

        mMainFrame = (FrameLayout) findViewById(R.id.main_frame);
        mMianNav = (BottomNavigationView) findViewById(R.id.main_nav);

        allResturant = new AllResturant();
        userprofile = new UserProfile();
        activityUser = new ActivityUser();

        //Listener for handling selection events on bottom navigation items
        mMianNav.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {

                switch (menuItem.getItemId()) {

                    case R.id.toprofile:
                        setFragment(userprofile);
                        return true;

                    case R.id.tohome:
                        setFragment(allResturant);
                        return true;

                    case R.id.toactivity:
                        setFragment(activityUser);
                        return true;

                    case R.id.tologout:
                        logout();
                        return true;

                    default:
                        return false;
                }
            }

            private void logout() {
                Intent intent = new Intent(BottomNavigation.this, Registration.class);
                intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
                startActivity(intent);
                finish();
            }

        });
    }

    private void setFragment(Fragment fragment) {
        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.main_frame, fragment);
        fragmentTransaction.commit();

    }
}

BottomNavigation.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=".BottomNavigation">

    <android.support.design.widget.BottomNavigationView
        android:id="@+id/main_nav"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:layout_alignParentEnd="true"
        android:layout_alignParentBottom="true"
        app:itemIconTint="@color/nav_items_color"
        app:itemTextColor="@color/nav_items_color"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="1.0"
        app:menu="@menu/nav_items" />

    <FrameLayout
        android:id="@+id/main_frame"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_above="@+id/main_nav"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        app:layout_constraintBottom_toTopOf="@+id/main_nav"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">

    </FrameLayout>
</android.support.constraint.ConstraintLayout>

它将如何自动显示？

Answer 1

设置UI后，请自行设置第一个片段。在onCreate()方法的最后一行添加下面的行。

setFragment(userprofile);

失败原因

因为您的活动开始时未调用onNavigationItemSelected，所以在用户切换屏幕时会调用它。

Answer 2

按以下说明修改创建的内容

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

    mMainFrame = (FrameLayout) findViewById(R.id.main_frame);
    mMianNav = (BottomNavigationView) findViewById(R.id.main_nav);

    allResturant = new AllResturant();
    userprofile = new UserProfile();
    activityUser = new ActivityUser();

       setFragment(userprofile);

    //Listener for handling selection events on bottom navigation items
    mMianNav.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {

            switch (menuItem.getItemId()) {

                case R.id.toprofile:
                    setFragment(userprofile);
                    return true;

                case R.id.tohome:
                    setFragment(allResturant);
                    return true;

                case R.id.toactivity:
                    setFragment(activityUser);
                    return true;

                case R.id.tologout:
                    logout();
                    return true;

                default:
                    return false;
            }
        }

        private void logout() {
            Intent intent = new Intent(BottomNavigation.this, Registration.class);
            intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
            startActivity(intent);
            finish();
        }

    });
}

Answer 3

您的代码几乎是完美的。您唯一要做的就是在创建Fragment时给Activity充气。

创建Activity后，您需要使用此行向您想要的Fragment充气一次：

setFragment(userprofile);

实例化片段后，可以将其放入onCreate方法中。之后，您的OnNavigationItemSelectedListener将负责填充片段。

片段活动不会自动显示

3 个答案:

失败原因