Material Design UI Widgets

Android L 开发者预览支持库提供两个新的Widgets，RecyclerView和CardView。使用这两个Widgets可以显示复杂的Listview和卡片布局，这两个Widgets默认使用Material design。

RecyclerView

RecyclerView是一个更高级柔性版本的Listview，RecyclerView是一个能包含很多视图的容器，它能完美的处理循环和滚动。在item动态变化的Listview使用RecyclerView。

RecyclerView使用很简单，因为它提供了：

1、定位item的布局管理器

2、常见的item操作默认动画

你能够灵活的为RecyclerView自定义布局管理器和动画。

使用RecyclerView，必须使用指定一个adapter、定义一个布局管理器。创建adapter必须继承自RecyclerView.Adapter。实施的细节需要看数据类型和需要的视图。



RecyclerView widget

RecyclerView 提供了 LayoutManager，RecylerView 不负责子 View 的布局，我们可以自定义 LayoutManager 来实现不同的布局效果，目前只提供了LinearLayoutManager。 LinearLayoutManager 可以指定方向，默认是垂直， 可以指定水平， 这样就轻松实现了水平的 ListView。

RecyclerView Demo：

1、布局文件

[html] view
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<!-- 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"/>

2、Activity文件

[java] view
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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;

}

}

3、Recycler adapter

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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 的标准化了 ViewHolder， 编写 Adapter 面向的是 ViewHoder 而不在是View 了， 复用的逻辑被封装了， 写起来更加简单。

CardView

CardView继承自FrameLayout类，可以在一个卡片布局中一致性的显示内容，卡片可以包含圆角和阴影。

可以使用android:elevation属性，创建一个阴影的卡片。

怎样指定CardView的属性：

1、使用android:cardCornerRadius属性指定圆角半径

2、使用CardView.setRadius 设置圆角半径。

3、使用 android:cardBackgroundColor属性设置卡片颜色

在创建布局文件中创建CardView：

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<!-- 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>