Square：从今天开始抛弃Fragment吧！

• 原文链接 : Advocating Against Android Fragments
• 原文作者 : Pierre-Yves Ricau
• 译文出自 : 开发技术前线 www.devtf.cn
• 译者 : chaossss
• 校对者: 这里校对者的github用户名
• 状态 : 完成

switch (f.mState) { case Fragment.INITIALIZING: if (f.mSavedFragmentState != null) {
            f.mSavedViewState = f.mSavedFragmentState.getSparseParcelableArray(
                    FragmentManagerImpl.VIEW_STATE_TAG);
            f.mTarget = getFragment(f.mSavedFragmentState,
                    FragmentManagerImpl.TARGET_STATE_TAG); if (f.mTarget != null) {
                f.mTargetRequestCode = f.mSavedFragmentState.getInt(
                        FragmentManagerImpl.TARGET_REQUEST_CODE_STATE_TAG, 0);
            }
            f.mUserVisibleHint = f.mSavedFragmentState.getBoolean(
                    FragmentManagerImpl.USER_VISIBLE_HINT_TAG, true); if (!f.mUserVisibleHint) {
                f.mDeferStart = true; if (newState > Fragment.STOPPED) {
                    newState = Fragment.STOPPED;
                }
            }
        } // ... }

class BackStackRecord extends FragmentTransaction { int commitInternal(boolean allowStateLoss) { if (mCommitted) throw new IllegalStateException("commit already called");
        mCommitted = true; if (mAddToBackStack) {
            mIndex = mManager.allocBackStackIndex(this);
        } else {
            mIndex = -1;
        }
        mManager.enqueueAction(this, allowStateLoss); return mIndex;
    }
}

DialogFragment dialogFragment = new DialogFragment() { @Override public Dialog onCreateDialog(Bundle savedInstanceState) { ... }
};
dialogFragment.show(fragmentManager, tag);

android.support.v4.app.Fragment$InstantiationException:
    Unable to instantiate fragment com.squareup.MyActivity$1:
    make sure class name exists, is public, and has an empty constructor that is public

public class HeadlinesFragment extends ListFragment { OnHeadlineSelectedListener mCallback; public interface OnHeadlineSelectedListener { void onArticleSelected(int position);
  } @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
    setListAdapter( new ArrayAdapter<String>(getActivity(),
            R.layout.fragment_list,
            Ipsum.Headlines));
  } @Override public void onAttach(Activity activity) { super.onAttach(activity);
    mCallback = (OnHeadlineSelectedListener) activity;
  } @Override public void onListItemClick(ListView l, View v, int position, long id) {
    mCallback.onArticleSelected(position);
    getListView().setItemChecked(position, true);
  }
}

public class ListFragmentActivity extends Activity implements HeadlinesFragment.OnHeadlineSelectedListener { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
    setContentView(R.layout.news_articles); if (findViewById(R.id.fragment_container) != null) { if (savedInstanceState != null) { return;
      }
      HeadlinesFragment firstFragment = new HeadlinesFragment();
      firstFragment.setArguments(getIntent().getExtras());
      getFragmentManager()
          .beginTransaction()
          .add(R.id.fragment_container, firstFragment)
          .commit();
    }
  } public void onArticleSelected(int position) {
    ArticleFragment articleFrag =
        (ArticleFragment) getFragmentManager()
            .findFragmentById(R.id.article_fragment); if (articleFrag != null) {
      articleFrag.updateArticleView(position);
    } else {
      ArticleFragment newFragment = new ArticleFragment();
      Bundle args = new Bundle();
      args.putInt(ArticleFragment.ARG_POSITION, position);
      newFragment.setArguments(args);
      getFragmentManager()
          .beginTransaction()
          .replace(R.id.fragment_container, newFragment)
          .addToBackStack(null)
          .commit();
    }
  }
}

public interface Container { void showItem(String item); boolean onBackPressed();
}

public class MainActivity extends Activity { private Container container; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
    setContentView(R.layout.main_activity);
    container = (Container) findViewById(R.id.container);
  } public Container getContainer() { return container;
  } @Override public void onBackPressed() { boolean handled = container.onBackPressed(); if (!handled) {
      finish();
    }
  }
}

public class ItemListView extends ListView { public ItemListView(Context context, AttributeSet attrs) { super(context, attrs);
  } @Override protected void onFinishInflate() { super.onFinishInflate(); final MyListAdapter adapter = new MyListAdapter();
    setAdapter(adapter);
    setOnItemClickListener(new OnItemClickListener() { @Override public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        String item = adapter.getItem(position);
        MainActivity activity = (MainActivity) getContext();
        Container container = activity.getContainer();
        container.showItem(item);
      }
    });
  }
}

<com.squareup.view.SinglePaneContainer  xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:id="@+id/container" > <com.squareup.view.ItemListView  android:layout_width="match_parent" android:layout_height="match_parent" /> </com.squareup.view.SinglePaneContainer>

<com.squareup.view.DualPaneContainer  xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="horizontal" android:id="@+id/container" > <com.squareup.view.ItemListView  android:layout_width="0dp" android:layout_height="match_parent" android:layout_weight="0.2" /> <include layout="@layout/detail" android:layout_width="0dp" android:layout_height="match_parent" android:layout_weight="0.8" /> </com.squareup.view.DualPaneContainer>

public class DualPaneContainer extends LinearLayout implements Container { private MyDetailView detailView; public DualPaneContainer(Context context, AttributeSet attrs) { super(context, attrs);
  } @Override protected void onFinishInflate() { super.onFinishInflate();
    detailView = (MyDetailView) getChildAt(1);
  } public boolean onBackPressed() { return false;
  } @Override public void showItem(String item) {
    detailView.setItem(item);
  }
}

public class SinglePaneContainer extends FrameLayout implements Container { private ItemListView listView; public SinglePaneContainer(Context context, AttributeSet attrs) { super(context, attrs);
  } @Override protected void onFinishInflate() { super.onFinishInflate();
    listView = (ItemListView) getChildAt(0);
  } public boolean onBackPressed() { if (!listViewAttached()) {
      removeViewAt(0);
      addView(listView); return true;
    } return false;
  } @Override public void showItem(String item) { if (listViewAttached()) {
      removeViewAt(0);
      View.inflate(getContext(), R.layout.detail, this);
    }
    MyDetailView detailView = (MyDetailView) getChildAt(0);
    detailView.setItem(item);
  } private boolean listViewAttached() { return listView.getParent() != null;
  }
}

public class MyDetailView extends LinearLayout { TextView textView;
  DetailPresenter presenter; public MyDetailView(Context context, AttributeSet attrs) { super(context, attrs);
    presenter = new DetailPresenter();
  } @Override protected void onFinishInflate() { super.onFinishInflate();
    presenter.setView(this);
    textView = (TextView) findViewById(R.id.text);
    findViewById(R.id.button).setOnClickListener(new OnClickListener() { @Override public void onClick(View v) {
        presenter.buttonClicked();
      }
    });
  } public void setItem(String item) {
    textView.setText(item);
  }
}

class EditDiscountPresenter { // ... public void saveDiscount() {
    EditDiscountView view = getView();
    String name = view.getName(); if (isBlank(name)) {
      view.showNameRequiredWarning(); return;
    } if (isNewDiscount()) {
      createNewDiscountAsync(name, view.getAmount(), view.isPercentage());
    } else {
      updateNewDiscountAsync(discountId, name, view.getAmount(),
        view.isPercentage());
    }
    close();
  }
}

@Test public void cannot_save_discount_with_empty_name() {
  startEditingLoadedPercentageDiscount();
  when(view.getName()).thenReturn("");
  presenter.saveDiscount();
  verify(view).showNameRequiredWarning();
  assertThat(isSavingInBackground()).isFalse();
}

public class DetailFragment extends Fragment { @Override public View onCreateView(LayoutInflater inflater,
    ViewGroup container, Bundle savedInstanceState) { return inflater.inflate(R.layout.my_detail_view, container, false);
  }
}