挑戰練習8.8 RecyclerView ViewType

  請在RecyclerView中創建兩類列表項:一般性crime，以及需警方介入的crime。要完成這個挑戰，你需要用到RecyclerView.Adapter的視圖類別功能(view type)。在Crime對象里，再添加一個mRequiresPolice實例變量，使用它並借助getItemViewType(int)方法,確定該加載哪個視圖到CrimeAdapter。

  在onCreateViewHolder(ViewGroup,int)方法里，基於getItemViewType(int)方法返回的ViewType值，需要返回不同的ViewHolder。如果是一般性crime，就仍然使用原始布局;如果是需警方介入的crime，就使用一個帶聯系警方按鈕的新布局。

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1.題目要求兩類列表項，如果是需警方介入的crime，就使用一個帶聯系警方按鈕的新布局，因此添加一個新的xml布局文件

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="8dp">
    <TextView
        android:id="@+id/crime_title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Crime Title"/>

    <TextView
        android:id="@+id/crime_date"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Crime Date"/>
    <!--挑戰練習：新增一個報警按鈕-->
    <Button
        android:id="@+id/require_police"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="call 110"
        android:textAllCaps="false"/>
</LinearLayout>

2.在Crime對象里，再添加一個mRequiresPolice實例變量，並且為mRequiresPolice添加響應的getter和setter方法

package com.bignerdranch.android.criminalintent.entity;

import java.util.Date;
import java.util.UUID;

public class Crime {
    private UUID mId;
    private String mTitle;
    private Date mDate;
    private boolean mSolved;
    //題目要求的是否叫警察
    private boolean mRequiresPolice;

    public Crime() {
        this.mId = UUID.randomUUID();
        this.mDate = new Date();
    }

    public UUID getmId() {
        return mId;
    }

    public String getmTitle() {
        return mTitle;
    }

    public void setmTitle(String mTitle) {
        this.mTitle = mTitle;
    }

    public Date getmDate() {
        return mDate;
    }

    public void setmDate(Date mDate) {
        this.mDate = mDate;
    }

    public boolean ismSolved() {
        return mSolved;
    }

    public void setmSolved(boolean mSolved) {
        this.mSolved = mSolved;
    }

    public boolean ismRequiresPolice() {
        return mRequiresPolice;
    }

    public void setmRequiresPolice(boolean mRequiresPolice) {
        this.mRequiresPolice = mRequiresPolice;
    }
}

3.在CrimeLab中賦值，每10個就是需要警方介入的crime

public  CrimeLab(Context context) {
        mCrimes = new ArrayList<>();
        for (int i = 0; i < 100; i++) {
            Crime crime = new Crime();
            crime.setmTitle("Crime #" + i);
            crime.setmSolved(i % 2 == 0);
            //每隔10個就是需警方介入的crime
            crime.setmRequiresPolice(i % 10 == 0);
            mCrimes.add(crime);
        }
    }

4.在原本CrimeHolder的基礎下新增一個requirePoliceCrimeHolder內部類

 //定義一個新的requirePoliceCrimeHolder內部類一個CrimeHolder對應一行列表項，對應布局為 list_item_require_crime
    private class requirePoliceCrimeHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
        private TextView mTitleTextView;
        private TextView mDateTextView;
        private Button mRequirePolice;
        private Crime mCrime;

        //只要收到一個crime，CrimeHolder就會刷新顯示mTitleTextView和mDateTextView
        private void bind(Crime crime) {
            mCrime = crime;
            mTitleTextView.setText(mCrime.getmTitle());
            mDateTextView.setText(mCrime.getmDate().toString());
        }

        public requirePoliceCrimeHolder(LayoutInflater inflater,ViewGroup parent) {
            //首先實例化 list_item_require_crime 布局然后傳給super（）即ViewHolder的構造方法*/
            super(inflater.inflate(R.layout.list_item_crime,parent,false));

            mTitleTextView = (TextView)itemView.findViewById(R.id.crime_title);
            mDateTextView = (TextView)itemView.findViewById(R.id.crime_date);
            mRequirePolice = (Button)itemView.findViewById(R.id.require_police);
            itemView.setOnClickListener(this);
        }

        @Override
        public void onClick(View v) {
            Toast.makeText(getActivity(),"Require Police!",Toast.LENGTH_SHORT).show();
        }
    }

5.適配器CrimeAdapter，現在多了requirePoliceCrimeHolder，適配器就不能專門用泛型接收CrimeHolder了， 在onCreateViewHolder(ViewGroup,int)方法里，基於getItemViewType(int)方法返回的ViewType值，需要返回不同的ViewHolder。

 public class CrimeAdapter extends RecyclerView.Adapter {
        private List<Crime> mCrimes;
        public CrimeAdapter(List<Crime> crimes) {
            mCrimes = crimes;
        }
        //視圖類別功能
        @Override
        public int getItemViewType(int position) {
            //真不報警
            if(mCrimes.get(position).ismRequiresPolice()) {
                return 1;
            }else{
                return 0;
            }
        }
        @NonNull
        @Override
        public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
            //先創建LayoutInflater
            LayoutInflater layoutInflater=LayoutInflater.from(getActivity());

            //判斷上面的i的值判斷使用什么布局，即getItemViewType的返回值
            if (i == 1)
                return new requirePoliceCrimeHolder(layoutInflater, viewGroup);
            else
                return new CrimeHolder(layoutInflater, viewGroup);
        }

        //需要綁定數據（上下滑動屏幕）時，就會讀取當前位置並綁定
        @Override
        public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
            if (holder instanceof CrimeHolder) {    //instance,如果左側的對象是右側類的實例，則返回true
                Crime crime = mCrimes.get(position);
                ((CrimeHolder)holder).bind(crime);
            }else if (holder instanceof requirePoliceCrimeHolder){
                Crime crime = mCrimes.get(position);
                ((requirePoliceCrimeHolder)holder).bind(crime);
            }
        }

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

6.運行效果:

 

 

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