java - 检查用户是否选择了 fragment 项目

Question

我想检查用户是否选择了 fragment 项目[主页、搜索、发布、通知、个人资料]，如果用户选择了其中任何一个，我想禁止在所选 fragment Activity 之前再次选择相同的 Activity 。

另外，在“主页” Activity 中，我有一个包含 X 个项目的回收器 View ，如果我再次单击主页 Activity 而不是禁用它，我想移动适配器以查看回收器 View 中的第一个项目 [灵感来自 Instagram 的想法]您单击主页，它会将您定向到顶部帖子。

我尝试调用fragmentactivity的Id但无法工作

package com.capstone.araba;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.os.Handler;
import android.view.MenuItem;

import com.capstone.araba.Fragments.HomeFragment;
import com.capstone.araba.Fragments.NotificationFragment;
import com.capstone.araba.Fragments.ProfileFragment;
import com.capstone.araba.Fragments.SearchFragment;
import com.google.android.material.bottomnavigation.BottomNavigationView;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;

import java.util.Objects;

import androidx.fragment.app.Fragment;
import androidx.swiperefreshlayout.widget.SwipeRefreshLayout;


public class MainActivity extends AppCompatActivity {

    BottomNavigationView bottom_navigation;
    Fragment selectedfragment = null;
    private FirebaseUser user;
    private static MainActivity mInstance;



    public static synchronized MainActivity getInstance() {
        return mInstance;
    }

    public void setConnectivityListener(ConnectivityReceiver.ConnectivityReceiverListener listener) {
        ConnectivityReceiver.connectivityReceiverListener = listener;
    }

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

        mInstance = this;

        bottom_navigation = findViewById(R.id.bottom_navigation);
        bottom_navigation.setOnNavigationItemSelectedListener(navigationItemSelectedListener);


        Bundle intent = getIntent().getExtras();
        if (intent != null){
            String publisher = intent.getString("publisherid");

            SharedPreferences.Editor editor = getSharedPreferences("PREFS", MODE_PRIVATE).edit();
            editor.putString("profileid", publisher);
            editor.apply();

            getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                    new ProfileFragment()).commit();
        } else {
            getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                    new HomeFragment()).commit();
        }

    }


    private BottomNavigationView.OnNavigationItemSelectedListener navigationItemSelectedListener =
            new BottomNavigationView.OnNavigationItemSelectedListener() {

                @Override
                public boolean onNavigationItemSelected( MenuItem item) {
                    user = FirebaseAuth.getInstance().getCurrentUser();

                    switch (item.getItemId()){
                        case R.id.nav_home:
                            selectedfragment = new HomeFragment();

                            break;
                        case R.id.nav_search:
                            selectedfragment = new SearchFragment();
                            break;
                        case R.id.nav_add:
                            selectedfragment = null;
                            startActivity(new Intent(MainActivity.this, PostActivity.class));
                            break;
                        case R.id.nav_heart:
                            selectedfragment = new NotificationFragment();
                            break;
                        case R.id.nav_profile:
                            if(user != null) {
                                SharedPreferences.Editor editor = getSharedPreferences("PREFS", MODE_PRIVATE).edit();
                                editor.putString("profileid", Objects.requireNonNull(FirebaseAuth.getInstance().getCurrentUser()).getUid());
                                editor.apply();
                                selectedfragment = new ProfileFragment();
                                break;
                            }
                            else{
                                Intent i = new Intent(MainActivity.this, GuestActivity.class);
                                startActivity(i);
                            }
                    }
                    if (selectedfragment != null) {
                        getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,
                                selectedfragment).commit();
                    }

                    return true;
                }
            };
}

因此，这背后的想法是不要让 Activity 每次我单击我已经所在的 fragment Activity 时总是重新启动或刷新...

Answer 1

覆盖onNavigationItemReselected(...):

• 检查主页是否已选择，然后执行您想要的操作。

这应该可以解决这两个问题，因为当您重新选择搜索、发布或其他任何内容时，您没有在被覆盖的方法中涵盖该案例，因此它不会执行任何操作。