Android RecyclerView線性布局詳解(1)

2019-10-23 19:45:05

字體：大中小

來源：轉載

供稿：網(wǎng)友

RecyclerView是Android 5.0新增的控件，在android-support-v7下面。官方文檔對RecycleView介紹很簡潔到位，如下：

A flexible view for providing a limited window into a large data set.
大概意思就是說：在有限大小的窗口里顯示大量數(shù)據(jù)的一個靈活的view。

下面是ReccleView繼承圖：

Android,RecyclerView,線性布局

看到這里我們自然想到了與之類似的控件ListView，RecyclerView和ListView都是在有限的屏幕區(qū)域里維護少量的View來進行顯示大量的數(shù)據(jù)，其實RecyclerView是ListView的升級版，功能更加強大，更加靈活，擴展性更強，Google建議使用RecycleView替代ListView。

下面是RecycleView結構圖：

Android,RecyclerView,線性布局

RecycleView主要包括以下幾個部件：

1. RecyclerView.Adapter

數(shù)據(jù)和視圖的分離設計是程序解耦和可維護的重要指標，RecycleView作為展示大量數(shù)據(jù)的view肯定是遵循這個設計的，ListView也不例外。通過繼承RecycleView.Adapter即可輕松實現(xiàn)自己的adapter，主要重寫RecycleView.Adapter的下面三個方法即可實現(xiàn)：

public MyRecycleViewAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) public void onBindViewHolder(MyRecycleViewAdapter.MyViewHolder holder, int position)public int getItemCount()

上面MyRecycleViewAdapter是我自己定義的ViewHolder

2. ViewHolder

ViewHolder用來保存列表中item view引用的類，這樣做的目的是重用item視圖，從而提高性能。
在ListView中，ViewHolder不是ListView自帶的，是需要自己定義的，當然你也可以不使用ViewHolder，這樣的后果就是ListView每次調用getView()方法的時候都會調用findViewById()方法，要知道findViewById()性能很差，它通過遞歸的方式去從view樹中找特定的子view的，最終往往帶來很差的性能體驗，所以使用ViewHolder也成了優(yōu)化ListView最重要的手段。
在RecyclerView中，Android內置了RecyclerView.ViewHolder，這意味著ViewHolder使用成了必須。

3. 分割線 RecycleView.ItemDecoration

ListView添加分割線很簡單，只需在ListView的xml中配置”divider”屬性即可，如：

android:dividerHeight="2dp"android:divider="@color/red"

但RecycleView添加分割線是比較麻煩的，并且默認是不帶分割線的。但實際開發(fā)中一般都需要分割線，使用RecycleView.ItemDecoration為RecycleView添加分割線

4. 布局管理器 LayoutManager

RecycleView支持多種布局模式：

1、LinearLayoutManager
線性布局管理器，支持水平布局和垂直布局兩種
2、GridLayoutManager
網(wǎng)格布局管理器
3、StaggerdGridLayoutManager
錯列的網(wǎng)格布局管理器，可以實現(xiàn)瀑布流列表

RecycleView使用時和ListView很類似，直接看一個簡單的例子，分別展示一個垂直方向和水平方向上的列表，并且都支持使用顏色和圖片做分割線，效果圖如下：

Android,RecyclerView,線性布局

1. MainActivity

package com.cjl.recycleviewtest;...public class MainActivity extends AppCompatActivity { private VerticalFragment mVerticalFragment; private HorizontalFragment mHorizontalFragment; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); //垂直 mVerticalFragment = new VerticalFragment(); //水平 mHorizontalFragment = new HorizontalFragment(); //默認為設置垂直 getFragmentManager().beginTransaction().replace(R.id.activity_main, mVerticalFragment).commit(); } @Override public boolean onCreateOptionsMenu(Menu menu) { MenuInflater inflater = getMenuInflater(); inflater.inflate(R.menu.menu_recycleview, menu); return super.onCreateOptionsMenu(menu); } @Override public boolean onOptionsItemSelected(MenuItem item) { int id = item.getItemId(); switch (id) {  //垂直方向  case R.id.vertical:  VerticalFragment mVerticalFragment = new VerticalFragment();  getFragmentManager().beginTransaction().replace(R.id.activity_main, mVerticalFragment).commit();  break;  //水平方向  case R.id.horizontal: getFragmentManager().beginTransaction().replace(R.id.activity_main, mHorizontalFragment).commit();  break; } return super.onOptionsItemSelected(item); }}

MainActivity布局文件 R.layout.activity_main

<?xml version="1.0" encoding="utf-8"?><FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/activity_main" android:layout_width="match_parent" android:layout_height="match_parent"></FrameLayout>

2. 垂直方向上 VerticalFragment

public class VerticalFragment extends Fragment implements View.OnClickListener{ private RecyclerView mRecycleViewDrawable; private RecyclerView mRecycleViewColor; private LinearLayoutManager mManagerColor; private LinearLayoutManager mManagerDrawable; private List<String> mData; private Button mDrawable; private Button mColor; private MyRecycleViewAdapter mRecycleViewAdapter; @Nullable @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View view = inflater.inflate(R.layout.fragment_vertical_layout, container, false); mRecycleViewDrawable = (RecyclerView) view.findViewById(R.id.recycleview_drawable); mRecycleViewColor = (RecyclerView) view.findViewById(R.id.recycleview_color); mDrawable = (Button) view.findViewById(R.id.btn_drawable); mDrawable.setOnClickListener(this); mColor = (Button) view.findViewById(R.id.btn_color); mColor.setOnClickListener(this); //1. 顏色分割線 mManagerColor = new LinearLayoutManager(getActivity()); mManagerColor.setOrientation(LinearLayoutManager.VERTICAL); mRecycleViewColor.setLayoutManager(mManagerColor); //設置顏色分割線 mRecycleViewColor.addItemDecoration(new LinearDivider(getActivity(), LinearLayoutManager.VERTICAL, 10, this.getResources().getColor(R.color.colorAccent))); //2. 圖片分割線 mManagerDrawable = new LinearLayoutManager(getActivity()); mManagerDrawable.setOrientation(LinearLayoutManager.VERTICAL); mRecycleViewDrawable.setLayoutManager(mManagerDrawable); //設置圖片分割線 Drawable drawable = ContextCompat.getDrawable(getActivity(), R.mipmap.divider); mRecycleViewDrawable.addItemDecoration(new LinearDivider(getActivity(), LinearLayoutManager.VERTICAL, 20, drawable)); mData = new ArrayList<String>(); initData(mData); //自定義adapter mRecycleViewAdapter = new MyRecycleViewAdapter(getActivity(), R.layout.item_vertical_recycleview, mData); //設置adapter mRecycleViewColor.setAdapter(mRecycleViewAdapter); mRecycleViewDrawable.setAdapter(mRecycleViewAdapter); return view; } private void initData(List<String> dataList) { for (int i = 0; i < 30; i++) {  dataList.add("item" + i); } } @Override public void onClick(View view) { int id = view.getId(); switch (id){  case R.id.btn_drawable:  mRecycleViewColor.setVisibility(View.INVISIBLE);  mRecycleViewDrawable.setVisibility(View.VISIBLE);  break;  case R.id.btn_color:  mRecycleViewColor.setVisibility(View.VISIBLE);  mRecycleViewDrawable.setVisibility(View.INVISIBLE);  break; } }}

VerticalFragment 的布局文件 R.layout.fragment_vertical_layout

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent"> <android.support.v7.widget.RecyclerView android:id="@+id/recycleview_drawable" android:layout_width="match_parent" android:layout_height="match_parent" android:layout_marginBottom="60dp"/> <android.support.v7.widget.RecyclerView android:id="@+id/recycleview_color" android:layout_width="match_parent" android:layout_height="match_parent" android:layout_marginBottom="60dp" android:visibility="invisible"/> <LinearLayout android:id="@+id/lilayout" android:orientation="horizontal" android:layout_width="match_parent" android:layout_height="wrap_content" android:weightSum="2" android:layout_alignParentBottom="true"> <Button  android:id="@+id/btn_drawable"  android:layout_width="wrap_content"  android:layout_height="50dp"  android:text="圖片分割線"  android:gravity="center"  android:layout_weight="1"  android:background="@color/colorPrimary"/> <Button  android:id="@+id/btn_color"  android:layout_width="wrap_content"  android:layout_height="50dp"  android:text="顏色分割線"  android:gravity="center"  android:layout_weight="1"  android:background="@color/mytv"/> </LinearLayout></RelativeLayout>

3. 直接繼承RecyclerView.Adapter

public class MyRecycleViewAdapter extends RecyclerView.Adapter<MyRecycleViewAdapter.MyViewHolder> { private LayoutInflater mLayoutInflater; private List<String> mDataList; private int mItemLayout; public MyRecycleViewAdapter(Context context, int itemLayout, List<String> datalist) { mLayoutInflater = LayoutInflater.from(context); mItemLayout = itemLayout; mDataList = datalist; } @Override public MyRecycleViewAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { return new MyViewHolder(mLayoutInflater.inflate(mItemLayout, parent, false)); } @Override public void onBindViewHolder(MyRecycleViewAdapter.MyViewHolder holder, int position) { holder.mTextView.setText(mDataList.get(position)); } @Override public int getItemCount() { return mDataList.size(); } class MyViewHolder extends RecyclerView.ViewHolder { private TextView mTextView; public MyViewHolder(View itemView) {  super(itemView);  mTextView = (TextView) itemView.findViewById(R.id.tv); } }}

item布局文件 item_vertical_recycleview.xml

<?xml version="1.0" encoding="utf-8"?><FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="wrap_content"> <TextView android:id="@+id/tv" android:gravity="center" android:layout_width="match_parent" android:layout_height="60dp"/></FrameLayout>

4. 分割線 RecyclerView.ItemDecoration

public class LinearDivider extends RecyclerView.ItemDecoration { private Drawable mDividerDarwable; private int mOrientation; private int mDividerHight = 1; private Paint mColorPaint; public final int[] ATRRS = new int[]{  android.R.attr.listDivider }; /* orientation 方向 */ public LinearDivider(Context context, int orientation) { final TypedArray ta = context.obtainStyledAttributes(ATRRS); this.mDividerDarwable = ta.getDrawable(0); ta.recycle(); setOrientation(orientation); } /* int orientation 方向 int dividerHight 分割線的線寬 Drawable dividerDrawable 充當分割線的圖片 */ public LinearDivider(Context context, int orientation, int dividerHight, Drawable dividerDrawable) { this(context, orientation); mDividerHight = dividerHight; mDividerDarwable = dividerDrawable; } /* int orientation 方向 int dividerHight 分割線的線寬 int dividerColor 分割線的顏色 */ public LinearDivider(Context context, int orientation, int dividerHight, int dividerColor) { this(context, orientation); mDividerHight = dividerHight; mColorPaint = new Paint(); mColorPaint.setColor(dividerColor); } public void setOrientation(int orientation) { if (orientation != LinearLayoutManager.HORIZONTAL && orientation != LinearLayoutManager.VERTICAL) {  throw new IllegalArgumentException("方向參數(shù)錯誤！"); } mOrientation = orientation; } @Override public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) { super.onDraw(c, parent, state); if (mOrientation == LinearLayoutManager.HORIZONTAL) {  drawHorizontalDivider(c, parent); } else {  drawVirticalDivider(c, parent); } } //畫垂直分割線 public void drawVirticalDivider(Canvas c, RecyclerView parent) { int left = parent.getPaddingLeft(); int right = parent.getWidth() - parent.getPaddingRight(); 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.getBottom() + params.bottomMargin;  final int bottom = top + mDividerHight;  if (mDividerDarwable != null) {  mDividerDarwable.setBounds(left, top, right, bottom);  mDividerDarwable.draw(c);  }  if (mColorPaint != null) {  c.drawRect(left, top, right, bottom, mColorPaint);  } } } //畫水平分割線 public void drawHorizontalDivider(Canvas c, RecyclerView parent) { int top = parent.getPaddingTop(); int bottom = parent.getHeight() - parent.getPaddingBottom(); final int childCount = parent.getChildCount(); for (int i = 0; i < childCount; i++) {  final View child = parent.getChildAt(i);  RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();  final int left = child.getRight() + params.rightMargin;  final int right = left + mDividerHight;  if (mDividerDarwable != null) {  mDividerDarwable.setBounds(left, top, right, bottom);  mDividerDarwable.draw(c);  }  if (mColorPaint != null) {  c.drawRect(left, top, right, bottom, mColorPaint);  } } } @Override public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) { super.getItemOffsets(outRect, view, parent, state); if (mOrientation == LinearLayoutManager.HORIZONTAL) {  outRect.set(0, 0, 0, mDividerHight); } else {  outRect.set(0, 0, mDividerHight, 0); } }}

未完待續(xù)……

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