Android《第六章：RecycleView》

作者: 泅渡者 | 来源:发表于2017-09-30 10:22 被阅读82次

在这一章我会主要介绍一些比较新的组件的使用，这里相信大家好多人都已经在使用RecyclerView了吧？那我这里会简单的应用下RecyclerView。
RecyclerView是support.v7包中的控件，可以说是ListView和GridView的增强升级版。

RecyclerView的基本用法

RecyclerView 主要是用来显示大量数据集合时防止视图多次渲染。它提供了一种插拔式的体验，高度的解耦，异常的灵活，通过设置它提供的不同LayoutManager，ItemDecoration , ItemAnimator实现令人瞠目的效果。
我们来创建一个示例项目RecycleViewTest：
首先我们需要获得Recycle View的支持：

image.png

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.bsoft.recycleviewtest.MainActivity">

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

item_home.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical"
              android:layout_width="match_parent"
              android:layout_height="wrap_content">
    <TextView
        android:id="@+id/tv_desc"
        android:layout_width="match_parent"
        android:layout_height="49dp"
        android:text=""
        android:gravity="center"/>
</LinearLayout>

我们为了演示就不再去写特别复杂的界面了，接下来我们看看MainActivity.class。


public class MainActivity extends AppCompatActivity {

    private RecyclerView ryc_view;
    private TestAdapter adapter;
    private List<String> mDatas;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        initData();
        adapter = new TestAdapter(this, mDatas);
        ryc_view = (RecyclerView) findViewById(R.id.ryc_view);
        ryc_view.setLayoutManager(new LinearLayoutManager(this));
        ryc_view.setAdapter(adapter);
    }

    private void initData() {

        mDatas = new ArrayList<String>();
        for (int i = 'A'; i < 'z'; i++) {
            mDatas.add("" + (char) i);
        }

    }
}

TestAdapter.class

/**
 * Created by 泅渡者
 * Created on 2017/9/30.
 */

class TestAdapter extends RecyclerView.Adapter<TestAdapter.ViewHolder> {
    private Context mcontext;
    private List<String> mdata;

    public TestAdapter(Context mcontext, List<String> mdata) {
        this.mcontext = mcontext;
        this.mdata = mdata;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {


        ViewHolder holder = new ViewHolder(LayoutInflater.from(mcontext).inflate(R.layout.item_home, parent,
                false));
        return holder;
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        holder.tv_desc.setText(mdata.get(position));
    }

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

    public class ViewHolder extends RecyclerView.ViewHolder {

        TextView tv_desc;

        public ViewHolder(View itemView) {
            super(itemView);
            tv_desc = (TextView) itemView.findViewById(R.id.tv_desc);
        }
    }
}

到这里我们的第一个RecyclerView例子就已经可以运行了。

image.png

是不是很丑，对了我们发现RecycleView怎么没有分割线呢。但是RecycleView组件是没有Divider来设置的，这时大部分人想到的是我会在Item布局底部加一条线，同样也能解决问题。
但其实RecycleView 是有提供使用的mRecyclerView.addItemDecoration() ；
代码如下：

/**
 * This class is from the v7 samples of the Android SDK. It's not by me!
 *
 * See the license above for details.
 */
public class DividerItemDecoration extends RecyclerView.ItemDecoration {

    private static final int[] ATTRS = new int[]{
            android.R.attr.listDivider
    };

    public static final int HORIZONTAL_LIST = LinearLayoutManager.HORIZONTAL;

    public static final int VERTICAL_LIST = LinearLayoutManager.VERTICAL;

    private Drawable mDivider;

    private int mOrientation;

    public DividerItemDecoration(Context context, int orientation) {
        final TypedArray a = context.obtainStyledAttributes(ATTRS);
        mDivider = a.getDrawable(0);
        a.recycle();
        setOrientation(orientation);
    }

    public void setOrientation(int orientation) {
        if (orientation != HORIZONTAL_LIST && orientation != VERTICAL_LIST) {
            throw new IllegalArgumentException("invalid orientation");
        }
        mOrientation = orientation;
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent) {

        if (mOrientation == VERTICAL_LIST) {
            drawVertical(c, parent);
        } else {
            drawHorizontal(c, parent);
        }

    }


    public void drawVertical(Canvas c, RecyclerView parent) {
        final int left = parent.getPaddingLeft();
        final int right = parent.getWidth() - parent.getPaddingRight();

        final int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            final View child = parent.getChildAt(i);
            android.support.v7.widget.RecyclerView v = new android.support.v7.widget.RecyclerView(parent.getContext());
            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                    .getLayoutParams();
            final int top = child.getBottom() + params.bottomMargin;
            final int bottom = top + mDivider.getIntrinsicHeight();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }

    public void drawHorizontal(Canvas c, RecyclerView parent) {
        final int top = parent.getPaddingTop();
        final int bottom = parent.getHeight() - parent.getPaddingBottom();

        final int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            final View child = parent.getChildAt(i);
            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                    .getLayoutParams();
            final int left = child.getRight() + params.rightMargin;
            final int right = left + mDivider.getIntrinsicHeight();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }

    @Override
    public void getItemOffsets(Rect outRect, int itemPosition, RecyclerView parent) {
        if (mOrientation == VERTICAL_LIST) {
            outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
        } else {
            outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
        }
    }
}

运行结果如下：

image.png

可以看到我们要完成一个ListView效果事如此的麻烦那么为什么官方还在大力推荐呢？接着往下看！

LayoutManager

上面实现了类似ListView样子的Demo，通过使用其默认的LinearLayoutManager。

RecyclerView.LayoutManager吧，这是一个抽象类，好在系统提供了3个实现类：

LinearLayoutManager 现行管理器，支持横向、纵向。
GridLayoutManager 网格布局管理器
StaggeredGridLayoutManager 瀑布就式布局管理器
上面我们已经初步体验了下LinearLayoutManager，接下来看GridLayoutManager。

GridLayoutManager
我们尝试去实现类似GridView，秒秒钟的事情：

//mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
mRecyclerView.setLayoutManager(new GridLayoutManager(this,4));

只需要修改LayoutManager即可，还是很nice的。
当然了，改为GridLayoutManager以后，对于分割线，前面的DividerItemDecoration就不适用了,因为每个Item一行，这样是没问题的。而GridLayoutManager时，一行有多个childItem，这样就多次绘制了，并且GridLayoutManager时，Item如果为最后一列（则右边无间隔线）或者为最后一行（底部无分割线）。
针对上述，我们编写了DividerGridItemDecoration。

public class DividerGridItemDecoration extends RecyclerView.ItemDecoration
{

    private static final int[] ATTRS = new int[] { android.R.attr.listDivider };
    private Drawable mDivider;

    public DividerGridItemDecoration(Context context)
    {
        final TypedArray a = context.obtainStyledAttributes(ATTRS);
        mDivider = a.getDrawable(0);
        a.recycle();
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, State state)
    {

        drawHorizontal(c, parent);
        drawVertical(c, parent);

    }

    private int getSpanCount(RecyclerView parent)
    {
        // 列数
        int spanCount = -1;
        LayoutManager layoutManager = parent.getLayoutManager();
        if (layoutManager instanceof GridLayoutManager)
        {

            spanCount = ((GridLayoutManager) layoutManager).getSpanCount();
        } else if (layoutManager instanceof StaggeredGridLayoutManager)
        {
            spanCount = ((StaggeredGridLayoutManager) layoutManager)
                    .getSpanCount();
        }
        return spanCount;
    }

    public void drawHorizontal(Canvas c, RecyclerView parent)
    {
        int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++)
        {
            final View child = parent.getChildAt(i);
            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                    .getLayoutParams();
            final int left = child.getLeft() - params.leftMargin;
            final int right = child.getRight() + params.rightMargin
                    + mDivider.getIntrinsicWidth();
            final int top = child.getBottom() + params.bottomMargin;
            final int bottom = top + mDivider.getIntrinsicHeight();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }

    public void drawVertical(Canvas c, RecyclerView parent)
    {
        final int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++)
        {
            final View child = parent.getChildAt(i);

            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                    .getLayoutParams();
            final int top = child.getTop() - params.topMargin;
            final int bottom = child.getBottom() + params.bottomMargin;
            final int left = child.getRight() + params.rightMargin;
            final int right = left + mDivider.getIntrinsicWidth();

            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }

    private boolean isLastColum(RecyclerView parent, int pos, int spanCount,
            int childCount)
    {
        LayoutManager layoutManager = parent.getLayoutManager();
        if (layoutManager instanceof GridLayoutManager)
        {
            if ((pos + 1) % spanCount == 0)// 如果是最后一列，则不需要绘制右边
            {
                return true;
            }
        } else if (layoutManager instanceof StaggeredGridLayoutManager)
        {
            int orientation = ((StaggeredGridLayoutManager) layoutManager)
                    .getOrientation();
            if (orientation == StaggeredGridLayoutManager.VERTICAL)
            {
                if ((pos + 1) % spanCount == 0)// 如果是最后一列，则不需要绘制右边
                {
                    return true;
                }
            } else
            {
                childCount = childCount - childCount % spanCount;
                if (pos >= childCount)// 如果是最后一列，则不需要绘制右边
                    return true;
            }
        }
        return false;
    }

    private boolean isLastRaw(RecyclerView parent, int pos, int spanCount,
            int childCount)
    {
        LayoutManager layoutManager = parent.getLayoutManager();
        if (layoutManager instanceof GridLayoutManager)
        {
            childCount = childCount - childCount % spanCount;
            if (pos >= childCount)// 如果是最后一行，则不需要绘制底部
                return true;
        } else if (layoutManager instanceof StaggeredGridLayoutManager)
        {
            int orientation = ((StaggeredGridLayoutManager) layoutManager)
                    .getOrientation();
            // StaggeredGridLayoutManager 且纵向滚动
            if (orientation == StaggeredGridLayoutManager.VERTICAL)
            {
                childCount = childCount - childCount % spanCount;
                // 如果是最后一行，则不需要绘制底部
                if (pos >= childCount)
                    return true;
            } else
            // StaggeredGridLayoutManager 且横向滚动
            {
                // 如果是最后一行，则不需要绘制底部
                if ((pos + 1) % spanCount == 0)
                {
                    return true;
                }
            }
        }
        return false;
    }

    @Override
    public void getItemOffsets(Rect outRect, int itemPosition,
            RecyclerView parent)
    {
        int spanCount = getSpanCount(parent);
        int childCount = parent.getAdapter().getItemCount();
        if (isLastRaw(parent, itemPosition, spanCount, childCount))// 如果是最后一行，则不需要绘制底部
        {
            outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
        } else if (isLastColum(parent, itemPosition, spanCount, childCount))// 如果是最后一列，则不需要绘制右边
        {
            outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
        } else
        {
            outRect.set(0, 0, mDivider.getIntrinsicWidth(),
                    mDivider.getIntrinsicHeight());
        }
    }
}

那我们看看运行结果：

image.png

Click and LongClick

RecyclerView虽然好，但是并没有提供ClickListener和LongClickListener。不过我们也可以自己去添加，只是会多了些代码而已。
示例代码如下

class TestAdapter extends RecyclerView.Adapter<TestAdapter.ViewHolder> {
    private Context mcontext;
    private List<String> mdata;

    public interface OnItemClickLitener
    {
        void onItemClick(View view, int position);
        void onItemLongClick(View view , int position);
    }

    private OnItemClickLitener mOnItemClickLitener;

    public void setOnItemClickLitener(OnItemClickLitener mOnItemClickLitener)
    {
        this.mOnItemClickLitener = mOnItemClickLitener;
    }

    public TestAdapter(Context mcontext, List<String> mdata) {
        this.mcontext = mcontext;
        this.mdata = mdata;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        ViewHolder holder = new ViewHolder(LayoutInflater.from(mcontext).inflate(R.layout.item_home, parent,
                false));
        return holder;
    }

    @Override
    public void onBindViewHolder(final ViewHolder holder, int position) {
        holder.tv_desc.setText(mdata.get(position));
        if (mOnItemClickLitener != null)
        {
            holder.itemView.setOnClickListener(new View.OnClickListener()
            {
                @Override
                public void onClick(View v)
                {
                    int pos = holder.getLayoutPosition();
                    mOnItemClickLitener.onItemClick(holder.itemView, pos);
                }
            });

            holder.itemView.setOnLongClickListener(new View.OnLongClickListener()
            {
                @Override
                public boolean onLongClick(View v)
                {
                    int pos = holder.getLayoutPosition();
                    mOnItemClickLitener.onItemLongClick(holder.itemView, pos);
                    return false;
                }
            });
        }
    }

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

    public class ViewHolder extends RecyclerView.ViewHolder {

        TextView tv_desc;

        public ViewHolder(View itemView) {
            super(itemView);
            tv_desc = (TextView) itemView.findViewById(R.id.tv_desc);
        }
    }
}

  adapter.setOnItemClickLitener(new TestAdapter.OnItemClickLitener() {

            @Override
            public void onItemClick(View view, int position) {
                Toast.makeText(MainActivity.this, position + " click",
                        Toast.LENGTH_SHORT).show();
            }

            @Override
            public void onItemLongClick(View view, int position) {
                Toast.makeText(MainActivity.this, position + " long click",
                        Toast.LENGTH_SHORT).show();
            }
        });

自此RecyclerView的基本用法就做了大概的介绍，现在如果要使用我们大可以找一些封装好的库，使用也方便。

Android《第六章：RecycleView》

RecyclerView的基本用法

LayoutManager

Click and LongClick

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