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
item_home.xml
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 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();
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 {
private Context mcontext;
private List mdata;
public TestAdapter(Context mcontext, List 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 {
private Context mcontext;
private List 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 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。