Material Design UI Widgets

 Android L 開發者預覽支持庫提供兩個新的Widgets，RecyclerView和CardView。使用這兩個Widgets能夠顯示覆雜的Listview和卡片佈局，這兩個Widgets默認使用Material design。

 

RecyclerView

    RecyclerView是一個更高級柔性版本的Listview，RecyclerView是一個能包含不少視圖的容器，它能完美的處理循環和滾動。在item動態變化的Listview使用RecyclerView。

 

RecyclerView使用很簡單，由於它提供了：

一、定位item的佈局管理器

二、常見的item操做默認動畫

 

你可以靈活的爲RecyclerView自定義佈局管理器和動畫。

使用RecyclerView，必須使用指定一個adapter、定義一個佈局管理器。建立adapter必須繼承自RecyclerView.Adapter。實施的細節須要看數據類型和須要的視圖。

   RecyclerView widget

 

 

    RecyclerView 提供了 LayoutManager，RecylerView 不負責子 View 的佈局，咱們能夠自定義 LayoutManager 來實現不一樣的佈局效果，目前只提供了LinearLayoutManager。 LinearLayoutManager 能夠指定方向，默認是垂直， 能夠指定水平， 這樣就輕鬆實現了水平的 ListView。

 

RecyclerView Demo：

一、佈局文件

 

<!-- A RecyclerView with some commonly used attributes -->
<android.support.v7.widget.RecyclerView
    android:id="@+id/my_recycler_view"
    android:scrollbars="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

二、Activity文件

public class MyActivity extends Activity {
    private RecyclerView mRecyclerView;
    private RecyclerView.Adapter mAdapter;
    private RecyclerView.LayoutManager mLayoutManager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.my_activity);
        mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);

        // improve performance if you know that changes in content
        // do not change the size of the RecyclerView
        mRecyclerView.setHasFixedSize(true);

        // use a linear layout manager
        mLayoutManager = new LinearLayoutManager(this);
        mRecyclerView.setLayoutManager(mLayoutManager);

        // specify an adapter (see also next example)
        mAdapter = new MyAdapter(myDataset);
        mRecyclerView.setAdapter(mAdapter);
    }
    ...
}
To create a simple adapter:

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
    private String[] mDataset;

    // Provide a reference to the type of views that you are using
    // (custom viewholder)
    public static class ViewHolder extends RecyclerView.ViewHolder {
        public TextView mTextView;
        public ViewHolder(TextView v) {
            super(v);
            mTextView = v;
        }
    }

    // Provide a suitable constructor (depends on the kind of dataset)
    public MyAdapter(String[] myDataset) {
        mDataset = myDataset;
    }

    // Create new views (invoked by the layout manager)
    @Override
    public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,
                                                   int viewType) {
        // create a new view
        View v = LayoutInflater.from(parent.getContext())
                               .inflate(R.layout.my_text_view, null);
        // set the view's size, margins, paddings and layout parameters
        ...
        ViewHolder vh = new ViewHolder(v);
        return vh;
    }

    // Replace the contents of a view (invoked by the layout manager)
    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        // - get element from your dataset at this position
        // - replace the contents of the view with that element
        holder.mTextView.setText(mDataset[position]);

    }

    // Return the size of your dataset (invoked by the layout manager)
    @Override
    public int getItemCount() {
        return mDataset.length;
    }
}

三、Recycler adapter

 

 

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
    private String[] mDataset;

    // Provide a reference to the type of views that you are using
    // (custom viewholder)
    public static class ViewHolder extends RecyclerView.ViewHolder {
        public TextView mTextView;
        public ViewHolder(TextView v) {
            super(v);
            mTextView = v;
        }
    }

    // Provide a suitable constructor (depends on the kind of dataset)
    public MyAdapter(String[] myDataset) {
        mDataset = myDataset;
    }

    // Create new views (invoked by the layout manager)
    @Override
    public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,
                                                   int viewType) {
        // create a new view
        View v = LayoutInflater.from(parent.getContext())
                               .inflate(R.layout.my_text_view, null);
        // set the view's size, margins, paddings and layout parameters
        ...
        ViewHolder vh = new ViewHolder(v);
        return vh;
    }

    // Replace the contents of a view (invoked by the layout manager)
    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        // - get element from your dataset at this position
        // - replace the contents of the view with that element
        holder.mTextView.setText(mDataset[position]);

    }

    // Return the size of your dataset (invoked by the layout manager)
    @Override
    public int getItemCount() {
        return mDataset.length;
    }
}

RecyclerView 的標準化了 ViewHolder， 編寫 Adapter 面向的是 ViewHoder 而不在是View 了， 複用的邏輯被封裝了， 寫起來更加簡單。

 

 

CardView

 

 

CardView繼承自FrameLayout類，能夠在一個卡片佈局中一致性的顯示內容，卡片能夠包含圓角和陰影。

 

能夠使用android:elevation屬性，建立一個陰影的卡片。

 

怎樣指定CardView的屬性：

一、使用android:cardCornerRadius屬性指定圓角半徑

二、使用CardView.setRadius 設置圓角半徑。

三、使用 android:cardBackgroundColor屬性設置卡片顏色

 

在建立佈局文件中建立CardView：

 

<!-- A CardView that contains a TextView -->
<android.support.v7.widget.CardView
    xmlns:card_view="http://schemas.android.com/apk/res-auto"
    android:id="@+id/card_view"
    android:layout_gravity="center"
    android:layout_width="200dp"
    android:layout_height="200dp"
    card_view:cardCornerRadius="4dp">

    <TextView
        android:id="@+id/info_text"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</android.support.v7.widget.CardView>