从 MainActivity 调用 Fragment 中的方法

Question

我的应用程序包含一个 MainActivity，其中包含一个 TabLayout。第二个选项卡有一个 RecyclerView 允许通过单击来选择项目。初始状态如左图所示。 When one or more items are selected however, a overlaying Toolbar is shown with the options to (from left to right) copy, edit, delete or deselect the items.这种情况如中图所示

When for example the deselect option is chosen, the Toolbar should hide and the items should be deselected.问题是我不知道如何让 RecyclerView 的 ListAdapter 知道应该取消选择那些项目。选择取消选择选项的当前结果如右图所示，因此 Toolbar 隐藏但项目没有取消选择。

困难在于 RecyclerView 在第二个片段中，称为 Fragment2，而带有选项的 Toolbar 是 MainActivity 布局的一部分. Fragment2 包含方法 deselect。此方法工作正常，但无法从 MainActivity.

调用它

为了解决这个问题，我尝试使用接口，但没有成功。第二种方式是在下面提供的代码中实现的。我试图在 onOptionsItemSelected 方法中调用 deselect，但它告诉我 fragment2 == null。我也尝试按照的建议进行操作，但我不知道在哪里给 fragment2 一个标签以及在我的情况下使用什么容器 ID。

如果您知道如何通过修改此方法或使用完全不同的方法来解决此问题，请告诉我！

MainActivity

import android.animation.Animator;
import android.content.Intent;
import android.graphics.PorterDuff;
import android.os.Build;
import android.support.design.widget.TabLayout;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.content.ContextCompat;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewAnimationUtils;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    ViewPager mViewPager;
    TabLayout tabLayout;
    Integer currentTab, fragmentID;
    boolean itemsSelected;

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


        mViewPager = findViewById(R.id.viewpager_main_activity);
        tabLayout = findViewById(R.id.tablayout_main_activity);
        tabLayout.setupWithViewPager(mViewPager);
        itemsSelected = false;

        displayDefaultAppbar();
        handleFragments(mViewPager);
        currentTab = handleStartupFragment(mViewPager, savedInstanceState);
    }

    private void displayDefaultAppbar() {
        final Toolbar toolbar = findViewById(R.id.toolbar_main_activity);
        TabLayout tabLayout = findViewById(R.id.tablayout_main_activity);
        setSupportActionBar(toolbar);
        if (getSupportActionBar() != null) {
            getSupportActionBar().setTitle(getResources().getString(R.string.app_name));
        }
        toolbar.setVisibility(View.VISIBLE);
        tabLayout.setVisibility(View.VISIBLE);
    }

    private void handleFragments(ViewPager mViewPager) {
        SectionsPagerAdapter mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
        mViewPager.setAdapter(mSectionsPagerAdapter);
        tabLayout.addOnTabSelectedListener(new TabLayout.ViewPagerOnTabSelectedListener(mViewPager) {
            @Override
            public void onTabSelected(TabLayout.Tab tab) {
                super.onTabSelected(tab);
                int tabIconColor = ContextCompat.getColor(MainActivity.this, android.R.color.holo_red_dark);
                if(tab.getIcon() != null) {
                    tab.getIcon().setColorFilter(tabIconColor, PorterDuff.Mode.SRC_IN);
                }
                currentTab = tab.getPosition();
                handleToolbarOptions(currentTab);
            }

            @Override
            public void onTabUnselected(TabLayout.Tab tab) {
                super.onTabUnselected(tab);
                int tabIconColor = ContextCompat.getColor(MainActivity.this, android.R.color.black);
                if(tab.getIcon() != null) {
                    tab.getIcon().setColorFilter(tabIconColor, PorterDuff.Mode.SRC_IN);
                }
            }

            @Override
            public void onTabReselected(TabLayout.Tab tab) {
                super.onTabReselected(tab);
            }
        });
    }

    private Integer handleStartupFragment(ViewPager mViewPager, Bundle savedInstanceState) {
        Intent intent = getIntent();
        Integer startupFragment;
        tabLayout.getTabAt(0).setText("1");
        tabLayout.getTabAt(1).setText("2");
        tabLayout.getTabAt(2).setText("3");
        if(intent.hasExtra("initialFragment")){
            Bundle bd = getIntent().getExtras();
            startupFragment = bd.getInt("initialFragment");
        } else {
            startupFragment = 1;
        }
        if (savedInstanceState == null) {
            mViewPager.setCurrentItem(startupFragment);
        }
        return startupFragment;
    }

    @Override
    public void onAttachFragment(Fragment fragment) {
        super.onAttachFragment(fragment);
        fragmentID = fragment.getId();
    }

    private void handleToolbarOptions(Integer currentTab) {
        Toolbar toolbar = findViewById(R.id.toolbar_main_activity);
        if (currentTab == 1) {
            toolbar.getMenu().clear();
            toolbar.inflateMenu(R.menu.fragment2);
        } else {
            toolbar.getMenu().clear();
            toolbar.inflateMenu(R.menu.other);
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        Toolbar toolbar = findViewById(R.id.toolbar_main_activity_selected);
        if (toolbar.isShown()) {
            getMenuInflater().inflate(R.menu.selected, menu);
        } else if (currentTab == 1) {
            getMenuInflater().inflate(R.menu.fragment2, menu);
        } else {
            getMenuInflater().inflate(R.menu.other, menu);
        }
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        if (item.getItemId() == R.id.selected_close) {
            if (findViewById(R.id.toolbar_main_activity_selected) != null) {
                hideSelectedToolbar();
                Fragment2 fragment2 = (Fragment2) getSupportFragmentManager().findFragmentById(R.id.tablayout_main_activity);
                if(fragment2 == null) {
                    Toast.makeText(this,"null",Toast.LENGTH_SHORT).show();
                } else if (!fragment2.isAdded()) {
                    Toast.makeText(this,"Not added",Toast.LENGTH_SHORT).show();
                } else {
                    fragment2.deselect();
                }
            }
            return true;
        } else {
            return super.onOptionsItemSelected(item);
        }
    }

    public void displaySelectedToolbar() {
        final Toolbar toolbar = findViewById(R.id.toolbar_main_activity_selected);
        toolbar.setVisibility(View.VISIBLE);
        if (Build.VERSION.SDK_INT >= 21) {
            toolbar.addOnLayoutChangeListener(new View.OnLayoutChangeListener() {
                @Override
                public void onLayoutChange(View view, int left, int top, int right, int bottom, int oldLeft, int oldTop, int oldRight, int oldBottom) {
                    Animator animator = ViewAnimationUtils.createCircularReveal(toolbar, toolbar.getWidth(), 0, 0,toolbar.getWidth());
                    animator.setDuration(ANIMATION_DURATION);
                    toolbar.removeOnLayoutChangeListener(this);
                    animator.start();
                }
            });
        }
        toolbar.setTitleTextColor(ContextCompat.getColor(MainActivity.this, android.R.color.black));
        setSupportActionBar(toolbar);
    }

    public void hideSelectedToolbar() {
        final Toolbar toolbar = findViewById(R.id.toolbar_main_activity_selected);
        if (Build.VERSION.SDK_INT >= 21) {
            Animator animator = ViewAnimationUtils.createCircularReveal(toolbar, toolbar.getWidth(), 0, toolbar.getWidth(), 0);
            animator.setDuration(ANIMATION_DURATION);
            animator.start();
            animator.addListener(new Animator.AnimatorListener() {
                @Override
                public void onAnimationStart(Animator animator) {

                }

                @Override
                public void onAnimationEnd(Animator animator) {
                    toolbar.setVisibility(View.GONE);
                    displayDefaultAppbar();
                }

                @Override
                public void onAnimationCancel(Animator animator) {

                }

                @Override
                public void onAnimationRepeat(Animator animator) {

                }
            });
        } else {
            toolbar.setVisibility(View.GONE);
            displayDefaultAppbar();
        }
    }

    private class SectionsPagerAdapter extends FragmentPagerAdapter {

        private SectionsPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int position) {
            switch (position) {
                case 0:
                    return new Fragment1();
                case 1:
                    return new Fragment2();
                case 2:
                    return new Fragment3();
                default:
                    return null;
            }
        }

        @Override
        public int getCount() {
            return 3;
        }
    }
}

片段2

import android.content.Context;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.CheckBox;
import android.widget.TextView;
import java.util.ArrayList;

public class Fragment2 extends Fragment {

    ListAdapter adapter;
    RecyclerView rv;
    ArrayList<TestItem> list;
    Integer selected, selectedOld;

    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment2, container, false);

        selected = 0;
        selectedOld = 0;

        list = new ArrayList<>();
        list.add(new TestItem("Item 1",false));
        list.add(new TestItem("Item 2",false));
        list.add(new TestItem("Item 3",false));
        list.add(new TestItem("Item 4",false));
        list.add(new TestItem("Item 5",false));
        list.add(new TestItem("Item 6",false));

        rv = rootView.findViewById(R.id.rv_fragment2);
        adapter = new ListAdapter(getActivity());
        rv.setAdapter(adapter);
        rv.setLayoutManager(new LinearLayoutManager(getActivity()));

        return rootView;
    }

    private void handleToolbar() {
        if (selected == 1 && selectedOld == 0) {
            if (getActivity() != null) {
                ((MainActivity) getActivity()).displaySelectedToolbar();
            }
        } else if (selected == 0 && selectedOld == 1) {
            if (getActivity() != null) {
                ((MainActivity) getActivity()).hideSelectedToolbar();
            }
        }
    }

    public void deselect() {
        for (int i=0; i<list.size(); i++) {
            list.get(i).setSelected(false);
        }
        adapter.notifyDataSetChanged();
        rv.setAdapter(adapter);
    }
}

activity_main.xml

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

    <android.support.design.widget.AppBarLayout
        android:id="@+id/appbarlayout_main_activity"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar_main_activity"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            app:layout_collapseMode="pin"
            app:layout_scrollFlags="scroll|enterAlways|snap"
            android:background="?attr/colorPrimary"
            android:visibility="visible"/>

        <android.support.design.widget.TabLayout
            android:id="@+id/tablayout_main_activity"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"/>

    </android.support.design.widget.AppBarLayout>

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager_main_activity"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar_main_activity_selected"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="@color/colorAccent"
        android:translationZ="4dp"
        android:visibility="invisible"/>

</android.support.design.widget.CoordinatorLayout>

fragment2.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:id="@+id/root_fragment2"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/rv_fragment2"
        android:paddingTop="150dp"
        android:paddingBottom="10dp"
        android:paddingStart="10dp"
        android:paddingEnd="10dp"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scrollbars="vertical"
        android:splitMotionEvents="false"
        android:clipToPadding="false"/>

</LinearLayout>

Answer 1

您可以使用的一种解决方案是 LocalBroadcastManager as you can see in this question.

片段2

private BroadcastReceiver mMessageReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            // you will be notified here, you can do your stuff(deselect) here
            String message = intent.getStringExtra("my_message");
            Log.d("receiver_message", "my_message = " + message);
        }
    };

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment2, container, false);

        LocalBroadcastManager.getInstance(getActivity()).registerReceiver(mMessageReceiver,
                new IntentFilter("my_event_tag"));

        return rootView;

    }

    @Override
    public void onDestroy() {
        LocalBroadcastManager.getInstance(getActivity()).unregisterReceiver(mMessageReceiver);
        super.onDestroy();
    }

MainActivity

private void callDeselectFromMainActivity() {
    Intent intent = new Intent("my_event_tag");
    intent.putExtra("my_message", "This is text should go to fragment...");
    LocalBroadcastManager.getInstance(this).sendBroadcast(intent);
}

当你从MainActivity调用callDeselectFromMainActivity方法时。它应该调用Fragment2中的onReceive方法。

Answer 2

您可以这样添加 class：

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.view.ViewGroup;

public class MainTabsPagerAdapter extends FragmentStatePagerAdapter {

    int mNoOfTabs;

    private OneFragment oneFragment;
    private TwoFragment twoFragment;
    private ThreeFragment threeFragment;

    public MainTabsPagerAdapter(FragmentManager fm, int numberOfTabs) {
        super(fm);
        mNoOfTabs = numberOfTabs;
    }

    @Override
    public Fragment getItem(int position) {
        switch (position) {
            case 0:
                return new oneFragment();
            case 1:
                return new twoFragment();
            case 2:
                return new threeFragment();
        }
        return null;
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        Fragment createdFragment = (Fragment) super.instantiateItem(container, position);
        switch(position){
            case 0:
                oneFragment = (OneFragment) createdFragment;
                break;
            case(1):
                twoFragment = (TwoFragment) createdFragment;
                break;
            case(2):
                threeFragment = (ThreeFragment) createdFragment;
                break;
        }
        return createdFragment;
    }

    public OneFragment getOneFragment() {
        return oneFragment;
    }

    public TwoFragment getTwoFragment() {
        return twoFragment;
    }

    public ThreeFragment getThreeFragment() {
        return threeFragment;
    }

    @Override
    public int getCount() {
        return mNoOfTabs;
    }
}

然后在你的 MainActivity 中添加：

@Override
protected void onCreate(Bundle savedInstanceState) {
    final String ONE_FRAGMENT = getString(R.string.one_fragment);
    final String TWO_FRAGMENT = getString(R.string.two_fragment);
    final String THREE_FRAGMENT = getString(R.string.three_fragment);

    mainTabLayout.addTab(mainTabLayout.newTab().setText(ONE_FRAGMENT));
    mainTabLayout.addTab(mainTabLayout.newTab().setText(TWO_FRAGMENT));
    mainTabLayout.addTab(mainTabLayout.newTab().setText(THREE_FRAGMENT));

    tabsPagerAdapter = new MainTabsPagerAdapter(getSupportFragmentManager(), mainTabLayout.getTabCount());
    mainViewPager.setAdapter(tabsPagerAdapter);
    mainViewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(mainTabLayout));
    mainTabLayout.addOnTabSelectedListener(this);
}

@Override
public void onTabSelected(TabLayout.Tab tab) {
    mainViewPager.setCurrentItem(tab.getPosition());
    mainToolbar.setTitle(firstCharToUpperCase(String.valueOf(tab.getText())));
}

@Override
public void onTabUnselected(TabLayout.Tab tab) {

}

@Override
public void onTabReselected(TabLayout.Tab tab) {

}

如果你想获得例如 OneFragment，你可以调用：

OneFragment oneFragment = tabsPagerAdapter.getOneFragment();
oneFragment.doSomething();

从 MainActivity 调用 Fragment 中的方法

Call method in Fragment from MainActivity

android

android-fragments

android-studio

android-recyclerview

android-tablayout