Android5.0(lollipop)新特性介绍（一）

今年6月的Google I/O大会上，Android L的初次见面我相信让会让很多android粉丝有些小激动和小期待，当然作为开发者的我来说，激动不言而喻，毕竟这是自08年以来改变最大的一个版本。新的设计语言(Material Design),5000多个新增api。废话不多说，今天要说的基本都是在Android5.0中很常见，也算是对自己学习的一种记录。

1.CardView

顾名思义，CardView 卡片视图，继承自framelayout，可以通过设置圆角以及阴影来展示带有像卡片一样的效果

用法：在布局声明CardView（注意：需要引入android-support-v7-cardview.jar）

<span style="font-size:14px;"><android.support.v7.widget.CardView
            android:id="@+id/cardview"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:elevation="100dp"
            card_view:cardBackgroundColor="@color/cardview_initial_background"
            card_view:cardCornerRadius="8dp"
            android:layout_marginLeft="@dimen/margin_large"
            android:layout_marginRight="@dimen/margin_large">
            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_margin="@dimen/margin_medium"
                android:text="@string/cardview_contents"/>
</android.support.v7.widget.CardView></span>

在Activity中通过调用mCardView.setRadius(progress)与mCardView.setElevation(progress)方法来分别设置CardView的圆角和阴影。

2.RecyclerView

RecyclerView的出现可以替代ListView和GridView，它标准化了ViewHolder，之前我们在写ListView的Adapter时需要自定义ViewHolder来提升ListView速度。使用RecyclerView的时候必须要设置LayoutManager，它会通知系统以什么样的布局来展示RecyclerView，目前系统提供了2种LayoutManager，LinearLayoutManager和GridLayoutManager对应着线性和格子，当然了也可以自定义LayoutManager来满足各种需求

用法：布局文件中声明RecyclerView(注意：需要引入android-support-v7-recyclerview.jar)

<span style="font-size:14px;"><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">
    <RadioGroup
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center_horizontal"
        android:orientation="horizontal"
        android:checkedButton="@+id/linear_layout_rb">
        <RadioButton android:id="@+id/linear_layout_rb"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/linear_layout_manager"/>
        <RadioButton android:id="@+id/grid_layout_rb"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/grid_layout_manager"/>
    </RadioGroup>

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
</LinearLayout></span>

在Activity中调用如下代码

<span style="font-size:14px;">mRecyclerView = (RecyclerView) rootView.findViewById(R.id.recyclerView);
//类似listview
mRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
//类似grdiview
mRecyclerView.setLayoutManager(new GridLayoutManager(getActivity(), 3));
mAdapter = new CustomAdapter(mDataset);
// Set CustomAdapter as the adapter for RecyclerView.
mRecyclerView.setAdapter(mAdapter);</span>

CustomAdapter代码如下

<span style="font-size:14px;">public class CustomAdapter extends RecyclerView.Adapter<CustomAdapter.ViewHolder> {
    private static final String TAG = "CustomAdapter";

    private String[] mDataSet;

    /**
     * Provide a reference to the type of views that you are using (custom ViewHolder)
     */
    public static class ViewHolder extends RecyclerView.ViewHolder {
        private final TextView textView;

        public ViewHolder(View v) {
            super(v);
            // Define click listener for the ViewHolder's View.
            v.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                }
            });
            textView = (TextView) v.findViewById(R.id.textView);
        }

        public TextView getTextView() {
            return textView;
        }
    }

    /**
     * Initialize the dataset of the Adapter.
     *
     * @param dataSet String[] containing the data to populate views to be used by RecyclerView.
     */
    public CustomAdapter(String[] dataSet) {
        mDataSet = dataSet;
    }

    // Create new views (invoked by the layout manager)
    @Override
    public ViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
        // Create a new view.
        View v = LayoutInflater.from(viewGroup.getContext())
                .inflate(R.layout.text_row_item, viewGroup, false);

        return new ViewHolder(v);
    }

    // Replace the contents of a view (invoked by the layout manager)
    @Override
    public void onBindViewHolder(ViewHolder viewHolder, final int position) {
        // Get element from your dataset at this position and replace the contents of the view
        // with that element
        viewHolder.getTextView().setText(mDataSet[position]);
        viewHolder.getTextView().setPadding(0, position, 0, 0);
    }

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

今天先介绍到这里，后续还会介绍FloatActionBar,触摸反馈，Activity过场动画等。

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