java - 如何初始化在 Activity 中定义的界面，该界面是通过 TabLayout 使用 ViewPager 设置的 3 个 fragment 实现的？

Question

我有一个 Activity ，其中包含带有 3 个 fragment 的 ViewPager 的 TabLayout 设置这 3 个 fragment 包含一些各自独特的方法，需要在单击按钮时调用它们，该按钮是菜单中的菜单项，将为这 3 个 fragment 的父 Activity 进行扩展。

现在我无法初始化名为 OnMenuSaveButonClickListener 的 Activity 中定义的界面，因为我收到错误:

Caused by: java.lang.ClassCastException: com.blah.blah.EditProductInfoActivity cannot be cast to com.blah.blah.EditProductInfoActivity$OnMenuSaveButonClickListener
   at com.blah.blah.EditProductInfoActivity.onCreate(EditProductInfoActivity.java:53)

使用 ViewPager 的父 Activity 代码(在 TabLayout 中包含 fragment ):

public class EditProductInfoActivity extends AppCompatActivity {

    TabLayout tabLayout;
    ViewPager mViewPager;
    OnMenuSaveButonClickListener mCallback;

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

        tabLayout = (TabLayout) findViewById(R.id.tabs);
        mViewPager = (ViewPager) findViewById(R.id.v_pager_prod);

        mCallback = (OnMenuSaveButonClickListener) this;  //line:53 with error
        initViewPager();

    private void initViewPager() {
        ArrayList<Fragment> fragments = new ArrayList<>();
        fragments.add(new CatalogueItemInfoFragment());
        fragments.add(new CatalogueItemInventoryFragment());
        fragments.add(new CatalogueItemNotesFragment());

        ProductTabsViewPagerAdapter productTabs = new ProductTabsViewPagerAdapter(
                getSupportFragmentManager(),this, fragments);
        mViewPager.setAdapter(productTabs);

        tabLayout.setupWithViewPager(mViewPager);
        tabLayout.getTabAt(0).setText("Product Info");
        tabLayout.getTabAt(1).setText("Inventory");
        tabLayout.getTabAt(2).setText("Notes");

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.item_info_menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        switch (item.getItemId()){
            case R.id.item_check:
                mCallback.onMenuButonClick();
                return true;

            default: return super.onOptionsItemSelected(item);
        }

    }

    public interface OnMenuSaveButonClickListener{
        void onMenuButonClick();
    }

}

ViewPager Adpater 类的代码:

public class ProductTabsViewPagerAdapter extends FragmentPagerAdapter {

    private Context context;
    private List<Fragment> fragments;

    public ProductTabsViewPagerAdapter(FragmentManager fm, Context context, List<Fragment> fragments) {

        super(fm);
        this.context = context;
        this.fragments = fragments;

    }

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

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

fragment 1 的代码:

public class CatalogueItemInfoFragment extends Fragment implements EditProductInfoActivity.OnMenuSaveButonClickListener {
    ...
    ...

    public void setItemFromItemForm(){

        productViewModel.setSize(productSizeText.getText().toString());
        productViewModel.setSizeSelection(productSizeSelectionText.getText().toString());
        productViewModel.setColor(productColorText.getText().toString());

    }

    @Override
    public void onMenuButonClick() {
        setItemFromItemForm();
    }

}

fragment 2 的代码:

public class CatalogueItemInventoryFragment extends Fragment implements EditProductInfoActivity.OnMenuSaveButonClickListener {

...
...

    private void setItemInventoryInfo() { 
         productViewModel.setAvailableQuantity(Integer.parseInt(availableQtyText.getText().toString()));
         productViewModel.setIsOutOfStock(outOfStockSwitch.isChecked());
         productViewModel.setIsShowOutOfStock(showOutOfStockSwitch.isChecked());
         productViewModel.setIsForceAllowOrder(forceAllowOrderSwitch.isChecked());
    }

    @Override
    public void onMenuButonClick() {

        setItemInventoryInfo();

    }

}

fragment 3 的代码:

public class CatalogueItemNotesFragment extends Fragment implements EditProductInfoActivity.OnMenuSaveButonClickListener {
    ...
    ...

    private void setItemMoreDetails() {

        mStaticProduct.setNotes(productNotesText.getText().toString());
        productViewModel.setNotes(productNotesText.getText().toString());

    }

    @Override
    public void onMenuButonClick() {
        setItemMoreDetails();
    }
}

Answer 1

1. 从 TabLayout 获取选定的选项卡位置，以便您可以定位当前可见的 fragment

   int selectedTab = tabLayout.getSelectedTabPosition();

2. 从该 fragment 调用OnMenuSaveButonClickListener实现方法

   ((OnMenuSaveButonClickListener)fragments.get(selectedTab)).onMenuButonClick();

此代码位于您的 Activity 中的onOptionsItemSelected您可以将该逻辑放入函数中，以避免对其他菜单项选项重复相同的行。

确保从代码中删除 mCallback 及其分配。

我建议您还从 Activity 中删除 OnMenuSaveButonClickListener 接口(interface)定义，并将其放在它自己的 .java (OnMenuSaveButonClickListener.java) > 松散耦合中。