Recyclerview在整个生命周期中都是空的

问题描述 投票：0回答：3

我有一个问题，让我疯了，并在网上搜索几个小时，但无法找到解决方案。我想在将新数据添加到列表时在recyclelerview中的第一个视图上设置动画。但我不能因为recyclerview为null。

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    orientation = getResources().getConfiguration().orientation;

    model = ViewModelProviders.of(getActivity()).get(ViewModelAdvices.class);
    model.getAdvices().observe(this, new Observer <List <Advice>>() {

        //Update recyclerview automatically when data is changed
        @Override
        public void onChanged(List <Advice> advices) {
            filtered_advices_list.clear();
            filtered_advices_list.addAll(advices);
            adapter_recycler_view.notifyDataSetChanged();

        }
    });
}

@Override
public void onResume() {
    super.onResume();
    Animation animation = AnimationUtils.loadAnimation(getContext(), R.anim.test_item);
    View v = recycler_view.getChildAt(0);
    v.startAnimation(animation);

}



@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.show_advices_fragment, container, false);

    setupLayoutDifferences(view);

    recycler_view = (RecyclerView) view.findViewById(R.id.recycler_view);
    layout_manager = new LinearLayoutManager(getContext());
    recycler_view.setLayoutManager(layout_manager);
    adapter_recycler_view = new AdapterRV(filtered_advices_list);
    recycler_view.setAdapter(adapter_recycler_view);

 spinner_1 = (Spinner) view.findViewById(R.id.spinner_1);
    adapter_spinner_1 = ArrayAdapter.createFromResource(view.getContext(), R.array.categories, android.R.layout.simple_spinner_item);
    adapter_spinner_1.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spinner_1.setAdapter(adapter_spinner_1);

    spinner_1.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
        @Override
        public void onItemSelected(AdapterView <?> parent, View view, int position, long id) {
            String category = spinner_1.getItemAtPosition(spinner_1.getSelectedItemPosition()).toString();
            model.setCategory(category);
        }
        @Override
        public void onNothingSelected(AdapterView <?> parent) { }
    });

    return view;
    }
}

show_advices_fragment

    <LinearLayout 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"
        android:orientation="vertical"
        android:background="@color/colorBlueGreen"
        android:paddingBottom="6dp">



    <Spinner
            android:id="@+id/spinner_1"
            android:layout_width="match_parent"
            android:layout_height="50dp"
            android:backgroundTint="@color/colorBlack" />

        <RelativeLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="bottom">

            <Button
                android:id="@+id/button_add_activity"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_alignParentBottom="true"
                android:layout_marginTop="6dp"
                android:layout_marginLeft="6dp"
                android:layout_marginRight="6dp"
                android:visibility="gone"
                android:text="@string/button_add_activity" />

            <androidx.recyclerview.widget.RecyclerView
                android:id="@+id/recycler_view"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:layout_above="@+id/button_add_activity"
                android:background="@color/colorLightGrey"
                android:scrollbars="vertical"
                />

        </RelativeLayout>

    </LinearLayout>

list_item_activity_main

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="4dp"
android:background="@color/colorWhite"
android:orientation="horizontal"
android:paddingBottom="5dp"
android:paddingTop="5dp"
android:paddingLeft="3dp"
android:paddingRight="3dp"
android:weightSum="3">

<TextView
    android:id="@+id/text_view_advice"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@drawable/border"
    android:textColor="@color/colorPrimary"
    android:paddingRight="4dp"
    android:layout_weight="1"
    android:text="TextView" />

<TextView
    android:id="@+id/text_view_author"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:textColor="@color/colorGrey"
    android:layout_weight="2"
    android:gravity="center"
    android:text="TextView" />

 </LinearLayout>

和test_item

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android"
    android:duration="@android:integer/config_longAnimTime">

    <translate
        android:interpolator="@android:anim/decelerate_interpolator"
        android:fromXDelta="100%p"
        android:toXDelta="0"
        />

    <alpha
        android:fromAlpha="0.5"
        android:toAlpha="1"
        android:interpolator="@android:anim/accelerate_decelerate_interpolator"
        />

</set>

在onResume中，我想在上一个生命周期中，并且已经在onCreateView中构建了recyclerview。我想在我到达onResume之前完成了recyclerview aint的建立，但我怎么能解决这个问题呢？如果我在片段已经加载时使用鼠标点击进行动画，它可以工作，但是当我切换片段并且再次构建recyclerview时，它不起作用。

java android
3个回答
0
投票

试试这个

@Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        orientation = getResources().getConfiguration().orientation;

        model = ViewModelProviders.of(getActivity()).get(ViewModelAdvices.class);
        model.getAdvices().observe(this, new Observer<List<Advice>>() {

            //Update recyclerview automatically when data is changed
            @Override
            public void onChanged(List<Advice> advices) {
                filtered_advices_list.clear();
                filtered_advices_list.addAll(advices);

            }
        });
    }

    @Override
    public void onResume() {
        super.onResume();
        Animation animation = AnimationUtils.loadAnimation(getContext(), R.anim.test_item);
        View v = recycler_view.getChildAt(0);
        v.startAnimation(animation);

    }


    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.show_advices_fragment, container, false);

        setupLayoutDifferences(view);

        recycler_view = (RecyclerView) view.findViewById(R.id.recycler_view);
        layout_manager = new LinearLayoutManager(getContext());
        recycler_view.setLayoutManager(layout_manager);
        populateAdapter();


        spinner_1 = (Spinner) view.findViewById(R.id.spinner_1);
        adapter_spinner_1 = ArrayAdapter.createFromResource(view.getContext(), R.array.categories, android.R.layout.simple_spinner_item);
        adapter_spinner_1.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinner_1.setAdapter(adapter_spinner_1);

        spinner_1.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                String category = spinner_1.getItemAtPosition(spinner_1.getSelectedItemPosition()).toString();
                model.setCategory(category);
            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {
            }
        });

        if (adapter_recycler_view != null){
            adapter_recycler_view.notifyDataSetChanged();
        }

        return view;
    }

    private void populateAdapter() {
        adapter_recycler_view = new AdapterRV(filtered_advices_list);
        recycler_view.setAdapter(adapter_recycler_view);
    }
0
投票

你不能依赖于片段中的onResume()，因为在某些Android版本上它不是100％在onCreateView()之后调用（更多细节在Fragment onResume() & onPause() is not called on backstack）。因此，您可能尚未完成片段布局创建。

您可以等到RecyclerView完成使用OnGlobalLayoutListener对所有项目进行充气，然后显示第一项的动画：

recycler_view.getViewTreeObserver()
             .addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
                 @Override
                public void onGlobalLayout() {

                  // show the animation
                  Animation animation = AnimationUtils.loadAnimation(getContext(), R.anim.test_item);
                  View v = recycler_view.getChildAt(0);
                  v.startAnimation(animation);

                  // remove listener so that this won't be called multiple time.
                  recycler_view.getViewTreeObserver().removeOnGlobalLayoutListener(this);
            }
        });
0
投票

谢谢你试图帮助我。问题是我的应用程序可能不是最好的组织，因此在我的recyclerview完成从ViewModel获取的列表之前，所有内容都会运行。但是在一个单独的线程上做动画就像一个魅力，然后我也可以完全控制动画。

if(action.equals("addData")) {

            Thread thread = new Thread() {
                @Override
                public void run() {
                    try {

                        boolean recycler_view_loading = true;

                        while(recycler_view_loading ) {
                            sleep(250);

                            if (recycler_view.getChildAt(0) != null) {

                                Animation animation = AnimationUtils.loadAnimation(getContext(), R.anim.item_animation_side);
                                View v = recycler_view.getChildAt(0);
                                v.startAnimation(animation);
                                recycler_view_loading  = false;
                            }
                        }
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            };
            thread.start();
        }
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