第二章（编写丑爆的聊天界面）

编写丑爆的聊天界面

编写聊天界面会使用到RecyclerView。

1. 首先我们建一个Msg类

package com.example.uibestpractice;

/**
 * Created by 侯允林 on 2018/5/25.
 */

public class Msg {
    public static final int TYPE_RECEIVED=0;
    public static final int TYPE_SENT=1;
    private String content;
    private int type;
    public Msg(String content,int type){
        this.content=content;
        this.type=type;
    }

    public int getType() {
        return type;
    }

    public String getContent() {
        return content;
    }
}

2. 接下来我们编写activity_main界面

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#d8e0e8"
    android:orientation="vertical"
    tools:context="com.example.uibestpractice.MainActivity">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/msg_recycler_view"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <EditText
            android:id="@+id/input_text"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:maxLines="2"
            android:hint="Type something here"/>
        <Button
            android:layout_height="wrap_content"
            android:layout_width="wrap_content"
            android:id="@+id/send"
            android:text="send"/>
    </LinearLayout>
</LinearLayout>

这里设置了一个背景色#d8e0e8

3. 接着编写Msg的子项布局msg_item

<?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="10dp">

    <LinearLayout
        android:id="@+id/left_layout"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="left"
        android:background="@drawable/messageleft">

        <TextView
            android:id="@+id/left_msg"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:layout_margin="10dp"
            android:textColor="#fff" />
    </LinearLayout>

    <LinearLayout
        android:id="@+id/right_layout"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="right"
        android:background="@drawable/messageright">

        <TextView
            android:id="@+id/right_msg"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:layout_margin="10dp" />
    </LinearLayout>
</LinearLayout>

这里虽然用了垂直的线性布局，有两个子项线性布局，但是在后面可以设置消息的类型然后将另一个子项现行布局Visibility设置成GONE，看下面：

4. 新建一个RecyclerView的适配器MsgAdapter

package com.example.uibestpractice;

import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.TextView;

import java.util.List;

/**
 * Created by 侯允林 on 2018/5/25.
 */

public class MsgAdapter extends RecyclerView.Adapter<MsgAdapter.ViewHolder> {
    List<Msg> mMsgList;

    public MsgAdapter(List<Msg> mMsgList) {
        this.mMsgList = mMsgList;
    }

    public static class ViewHolder extends RecyclerView.ViewHolder {
        LinearLayout leftlayout;
        LinearLayout rightlayout;
        TextView leftMsg;
        TextView rightMsg;

        public ViewHolder(View itemView) {
            super(itemView);
            leftlayout = (LinearLayout) itemView.findViewById(R.id.left_layout);
            rightlayout = (LinearLayout) itemView.findViewById(R.id.right_layout);
            leftMsg = (TextView) itemView.findViewById(R.id.left_msg);
            rightMsg = (TextView) itemView.findViewById(R.id.right_msg);
        }
    }

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

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        Msg msg = mMsgList.get(position);
        if (msg.getType() == Msg.TYPE_RECEIVED) {
            holder.rightMsg.setVisibility(View.GONE);
            holder.leftMsg.setVisibility(View.VISIBLE);
            holder.leftMsg.setText(msg.getContent());
        } else if (msg.getType() == Msg.TYPE_SENT) {
            holder.rightlayout.setVisibility(View.VISIBLE);
            holder.leftlayout.setVisibility(View.GONE);
            holder.rightMsg.setText(msg.getContent());
        }

    }

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


}

很简单的一个适配器类，看不明白的话建议去看我前面做的ListView和RecyclerView的笔记，这个只是在onBindViewHolder里面判断了消息的类型，并将另一个子项布局的可见性设置成GONE，发送的显示在右边，接收的显示在左边

5. 修改MainActivity

package com.example.uibestpractice;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    private List<Msg> msgList = new ArrayList<>();
    private EditText inputText;
    private Button send;
    private RecyclerView msgRecyclerView;
    private MsgAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        inputText = (EditText) findViewById(R.id.input_text);
        send = (Button) findViewById(R.id.send);
        msgRecyclerView = (RecyclerView) findViewById(R.id.msg_recycler_view);
        initMsgs();
        adapter = new MsgAdapter(msgList);
        LinearLayoutManager manager = new LinearLayoutManager(this);
        manager.setOrientation(LinearLayoutManager.VERTICAL);
        msgRecyclerView.setAdapter(adapter);
        msgRecyclerView.setLayoutManager(manager);
        send.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String content = inputText.getText().toString();
                if (!content.equals("")) {
                    Msg msg = new Msg(content, Msg.TYPE_SENT);
                    msgList.add(msg);
                    adapter.notifyItemInserted(msgList.size() - 1);//当有消息时刷新RecyclerView中的显示
                    adapter.notifyItemChanged(msgList.size() - 1);
                    msgRecyclerView.scrollToPosition(msgList.size() - 1);
                    inputText.setText("");
                }
            }
        });
    }

    private void initMsgs() {
        Msg msg1 = new Msg("hello", Msg.TYPE_RECEIVED);
        Msg msg2 = new Msg("who is that?", Msg.TYPE_SENT);
        Msg msg3 = new Msg("it's HouChongmu", Msg.TYPE_RECEIVED);
        msgList.add(msg1);
        msgList.add(msg2);
        msgList.add(msg3);
    }

}

adapter.notifyItemInserted(msgList.size() - 1)当有消息时刷新RecyclerView中的显示
msgRecyclerView.scrollToPosition(msgList.size() - 1)将RecyclerView定位到最后一项

总结：实际上显示

image

为什么有显示空的项目？