Android使用碎片的最佳实践——写个新闻应用

看了《第二行代码》一段时间了，这次按照书上的内容，用碎片写个新闻应用。
先新建一个空项目day07_FragmentBestPractice

一、一个新闻就是一个碎片

1、单个新闻的布局

news_content_frag.xml
头部显示新闻标题，正文显示新闻内容，中间使用一条细线View将其分隔开

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="match_parent">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/visibility_layout"
        android:orientation="vertical"
        android:visibility="invisible">

        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/news_title"
            android:gravity="center"
            android:padding="10dp"
            android:textSize="20sp"/>

        <View
            android:layout_width="match_parent"
            android:layout_height="1dp"
            android:background="#000"/>

        <TextView
            android:id="@+id/news_content"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1"
            android:padding="15dp"
            android:textSize="18sp" />

    </LinearLayout>
    
    <View
        android:layout_width="1dp"
        android:layout_height="match_parent"
        android:layout_alignParentLeft="true"
        android:background="#000"/>

</RelativeLayout>

2、将布局变成碎片

NewsContentFragment.java，其中用refresh()将标题和内容加载单个新闻的布局

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

    public void refresh(String newsTitle, String newsContent){
        View visibilityLayout = getView().findViewById(R.id.visibility_layout);
        visibilityLayout.setVisibility(View.VISIBLE);
        TextView newsTitleText = getView().findViewById(R.id.news_title);
        TextView newsContentText = getView().findViewById(R.id.news_content);
        newsTitleText.setText(newsTitle);
        newsContentText.setText(newsContent);
    }
}

二、一页新闻就是一个活动

新建一个活动NewsContentActivity和其对应的布局news_content.xml

1、一页新闻的布局

news_content.xml此时可以直接引入碎片类

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

</LinearLayout>

2、 将标题和内容传入碎片

NewsContentActivity.java
用FragmentManager的findFragmentById()得到NewsContentFragment实例，调用其refresh()方法就可以让其显示数据

public class NewsContentActivity extends AppCompatActivity {
    public static void actionStart(Context context, String newsTitle, String newsContent){
        Intent intent = new Intent(context, NewsContentActivity.class);
        intent.putExtra("news_title", newsTitle);
        intent.putExtra("news_content", newsContent);
        context.startActivity(intent);
    }

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

        String newsTitle = getIntent().getStringExtra("news_title"); // 获取传入的新闻标题
        String newsContent = getIntent().getStringExtra("news_content");
        NewsContentFragment newsContentFragment = (NewsContentFragment) getSupportFragmentManager().findFragmentById(R.id.news_content_fragment);
        newsContentFragment.refresh(newsTitle,newsContent);
    }
}

三、一堆新闻放到一个碎片

1、添加依赖库

app/build.gradle添加滚动控件Recyclerview

implementation 'androidx.recyclerview:recyclerview:1.0.0'

2、新闻列表的布局

news_titile_frag.xml

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

    <androidx.recyclerview.widget.RecyclerView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/news_title_recycler_view"/>

</LinearLayout>

子项布局news_item.xml
padding是内边距，android:ellipsize是文本超出控件宽度时的缩略方式，end指在尾部缩略

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/news_title"
    android:maxLines="1"
    android:ellipsize="end"
    android:textSize="18sp"
    android:paddingLeft="10dp"
    android:paddingRight="10dp"
    android:paddingTop="15dp"
    android:paddingBottom="15dp">
</TextView>

3、将布局变成碎片

NewsTitileFragment.java

public class NewsTitleFragment extends Fragment {
    private boolean isTwoPane;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.news_title_frag, container, false);
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        isTwoPane = getActivity().findViewById(R.id.news_content_layout) != null;
    }
}

在onActivityCreated()中，通过其能否在活动中找到id为news_content_layout的View来判断当前是单双页模式，这就要借助限定符了，下面我们将实现它

四、一张新闻列表是一个活动

1、默认单页模式

修改主布局activity_main.xml

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

    <fragment
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/news_title_fragment"
        android:name="com.example.day07_fragmentbestpractice.NewsTitleFragment"/>

</FrameLayout>

2、双页模式

新建layout-sw600dp目录，创建主布局activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    
    <fragment
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:id="@+id/news_title_fragment"
        android:name="com.example.day07_fragmentbestpractice.NewsTitleFragment"/>
    
    <FrameLayout
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="3"
        android:id="@+id/news_content_layout">
        
        <fragment
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:id="@+id/news_content_fragment"
            android:name="com.example.day07_fragmentbestpractice.NewsContentFragment"/>
        
    </FrameLayout>

</LinearLayout>

双页模式中有id为news_content_layout的View，这样刚才的第三步就不会报错了

3、类和适配器

我们在新闻列表页使用RecyclerView展示数据，所以要在这里建立对应的类和适配器

a、新闻类

News.java，新闻实体类

public class News {
    private String title;
    private String content;
    
    public String getTitle(){
        return title;
    }
    public void setTitile(String title){
        this.title = title;
    }
    
    public String getContent(){
        return content;
    }
    
    public void setContent(String content){
        this.content = content;
    }
}

b、适配器

修改NewsTitleFragment.java，将适配器作为内部类添加进去，可以直接访问内部变量

public class NewsTitleFragment extends Fragment {
    private boolean isTwoPane;
    
    ......

    class NewsAdapter extends RecyclerView.Adapter<NewsAdapter.ViewHolder>{
        private List<News> mNewsList;

        class ViewHolder extends RecyclerView.ViewHolder{
            TextView newsTitleText;
            public ViewHolder(View view){
                super(view);
                newsTitleText = (TextView) view.findViewById(R.id.news_title);
            }
        }

        @NonNull
        @Override
        public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.news_item, parent, false);
            final ViewHolder holder = new ViewHolder(view);
            view.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    News news = mNewsList.get(holder.getAdapterPosition());
                    if(isTwoPane){
                        NewsContentFragment newsContentFragment = (NewsContentFragment) getFragmentManager().findFragmentById(R.id.news_content_fragment);
                        newsContentFragment.refresh(news.getTitle(), news.getContent());
                    }else {
                        NewsContentActivity.actionStart(getActivity(),news.getTitle(),news.getContent());
                    }
                }
            });
            return holder;
        }
        
        public NewsAdapter(List<News> newsList) {
            mNewsList = newsList;
        }

        @Override
        public int getItemCount() {
            return mNewsList.size();
        }

        @Override
        public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
            News news = mNewsList.get(position);
            holder.newsTitleText.setText(news.getTitle());
        }
    }
}

五、一个新闻应用一下子完成

1、填充数据

修改NewsTitleFragment.java，完成初始化

public class NewsTitleFragment extends Fragment {

    ......

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.news_title_frag, container, false);
        RecyclerView newsTitleRecyclerView = view.findViewById(R.id.news_title_recycler_view);
        LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
        newsTitleRecyclerView.setLayoutManager(layoutManager);
        NewsAdapter adapter = new NewsAdapter(getNews());
        newsTitleRecyclerView.setAdapter(adapter);
        return view;
    }

    private List<News> getNews(){
        List<News> newsList = new ArrayList<>();
        for (int i = 1;i <= 100; i++){
            News news = new News();
            news.setTitle("这是新闻标题 "+ i);
            news.setContent(getRandomLengthContent("This is news content"+ i + "."));
            newsList.add(news);
        };
        return newsList;
    }

    private String getRandomLengthContent(String content) {
        Random random = new Random();
        int length = random.nextInt(20)+1;
        StringBuilder builder = new StringBuilder();
        for (int i = 0;i<length;i++){
            builder.append(content);
        }
        return builder.toString();
    }

}

2、运行

未点击标题

点击标题后


效果很不错！