Android L中的RecyclerView 、CardView 、Palette的使用
Android L版本中新增了RecyclerView、CardView 、Palette。RecyclerView、CardView为用于显示复杂视图的新增Widget。Palette作为调色板类,可以让你从图像中提取突出的颜色。
RecyclerView
RecyclerView作为替代ListView使用,RecyclerView标准化了ViewHolder,ListView中convertView是复用的,在RecyclerView中,是把ViewHolder作为缓存的单位了,然后convertView作为ViewHolder的成员变量保持在ViewHolder中,也就是说,假设没有屏幕显示10个条目,则会创建10个ViewHolder缓存起来,每次复用的是ViewHolder,所以他把getView这个方法变为了onCreateViewHolder。 ViewHolder更适合多种子布局的列表,尤其IM的对话列表。RecyclerView不提供setOnItemClickListener方法,你可以在ViewHolder中添加事件。
RecyclerView可以实现横向、纵向滑动视图:
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, 可以设置成水平。
RecyclerView Demo:
1、布局文件
<!-- 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"/>
2、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; } }
3、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; } }
设置横向:
@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_recycler_view_horizontal); // specify an adapter (see also next example) List<MyAdapter.Item> itemList = new ArrayList<MyAdapter.Item>(); for (int i = 0; i < 100; i++) itemList.add(new MyAdapter.Item("Item " + i, "world")); mAdapter = new MyAdapter(itemList); mRecyclerViewHorizontal = (RecyclerView) findViewById(R.id.my_recycler_view_horizontal); mRecyclerViewHorizontal.setHasFixedSize(true); // use a linear layout manager LinearLayoutManager mLayoutManager = new LinearLayoutManager(this); mLayoutManager.setOrientation(LinearLayoutManager.HORIZONTAL); mRecyclerViewHorizontal.setLayoutManager(mLayoutManager); mRecyclerViewHorizontal.setAdapter(mAdapter); }
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:
<!-- 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>
Palette
Palette从图像中提取突出的颜色,这样可以把色值赋给ActionBar、或者其他,可以让界面整个色调统一,效果见上图(Palette)。
Palette这个类中提取以下突出的颜色:
Vibrant (有活力)
Vibrant dark(有活力 暗色)
Vibrant light(有活力 亮色)
Muted (柔和)
Muted dark(柔和 暗色)
Muted light(柔和 亮色)
提取色值代码如下:
Bitmap bm = BitmapFactory.decodeResource(getResources(), item.image); Palette palette = Palette.generate(bm); if (palette.getLightVibrantColor() != null) { name.setBackgroundColor(palette.getLightVibrantColor().getRgb()); getSupportActionBar().setBackgroundDrawable(new ColorDrawable(palette.getLightVibrantColor().getRgb())); } }