android控件之CardView布局（卡片布局）

1.简介：CardView是用于实现卡片布局效果的重要控件，由appcompat-v7库提供，实际上CardView也是一个Fram

              eLayout,只是额外提供了圆角和阴影等效果，看上去由立体感。

               *app:cardCornerRadius属性制定卡片圆角的弧度。

               *app:elevation属性制定卡片的高度。即投影范围。

  *AppBarLayout:实际上是一个垂直方向上的LinearLayout，在内部做了很多滚动事件的封装，通过它可以解决Recycl

    e覆盖Toolbar的问题。

     解决步骤：1.将Toolbar嵌套到AppBarLayout中

                         2.给RecyclerView制定一个布局行为。app:layout_behavior="@string/appbar_scrolling_view_behavior"

    可以实现的效果：在嵌套的Toolbar中设置：app:layout_scrollFlags="scroll|enterAlways|snap"；scroll表示RecycleView

     向上滑动的时候，Toolbar会跟着一起向上滚动并实现隐藏，enterAlways表示RecycleView向下滚动的时候，Toolbar

     会跟着一起向下滚动并重新显示。snap表示当Toolbar还没有完全隐藏或者显示的时候，会根据当前滚动的距离，自

      动选择显示还是隐藏。

2.添加依赖

implementation 'com.android.support:cardview-v7:27.1.1'

3.fruit_item.xml布局

4.主布局

5.FruitAdapter和实体类

public class Fruit {
    private String name;
    private int imageId;

    public Fruit(String name, int imageId) {
        this.name = name;
        this.imageId = imageId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getImageId() {
        return imageId;
    }

    public void setImageId(int imageId) {
        this.imageId = imageId;
    }
}

public class FruitAdapter extends RecyclerView.Adapter{
    private Context mContext;
    private List mFruitList;

    public FruitAdapter(List fruitList){
        mFruitList=fruitList;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        if (mContext==null){
            mContext=parent.getContext();
        }
        View view=LayoutInflater.from(mContext).inflate(R.layout.fruit_item,
                parent,false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        Fruit fruit=mFruitList.get(position);
        holder.fruitName.setText(fruit.getName());
        Glide.with(mContext).load(fruit.getImageId()).into(holder.fruitImage);
    }

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

    static class ViewHolder extends RecyclerView.ViewHolder{
        CardView cardView;
        ImageView fruitImage;
        TextView fruitName;

        public ViewHolder(View itemView) {
            super(itemView);
            cardView= (CardView) itemView;
            fruitImage=itemView.findViewById(R.id.fruit_image);
            fruitName=itemView.findViewById(R.id.fruit_name);
        }
    }
}

6.代码

public class CardViewActiivity extends AppCompatActivity {
    private RecyclerView recyclerView;
    private DrawerLayout mDrawerLayout;
    private Fruit[] fruits={new Fruit("Apple",R.drawable.mm),
    new Fruit("Banana",R.drawable.mm),new Fruit("Orange",R.drawable.mm),
            new Fruit("Watermelon",R.drawable.mm),new Fruit("Pear",R.drawable.mm),
            new Fruit("Grape",R.drawable.mm),new Fruit("Pineapple",R.drawable.mm),
            new Fruit("Strawerry",R.drawable.mm),new Fruit("Cherry",R.drawable.mm),
            new Fruit("Mango",R.drawable.mm)};
    private List fruitList=new ArrayList<>();
    private FruitAdapter adapter;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.navigationview_activity);
        recyclerView=findViewById(R.id.recycle_view);
        initFruit();
        GridLayoutManager layoutManager=new GridLayoutManager(this,2);
        recyclerView.setLayoutManager(layoutManager);
        adapter=new FruitAdapter(fruitList);
        recyclerView.setAdapter(adapter);
    }

    private void initFruit(){
        fruitList.clear();
        for (int i=0;i<50;i++){
            Random random=new Random();
            int index=random.nextInt(fruits.length);
            fruitList.add(fruits[index]);
        }
    }
}