Android编写聊天界面

文件目录

在app下的build.gradle中添加依赖库（RecyclerView）

apply plugin: 'com.android.application'

android {
    compileSdkVersion 24
    buildToolsVersion "26.0.1"
    defaultConfig {
        applicationId "com.example.uibestpractice"
        minSdkVersion 15
        targetSdkVersion 24
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguarrules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'com.android.support:appcompat-v7:24.2.1'
    compile 'com.android.support.constraint:constraint-layout:1.0.2'
    compile 'com.android.support:recyclerview-v7:24.2.1'//添加RecyclerView依赖库
    testCompile 'junit:junit:4.12'
}

编写主界面（activity_main.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="match_parent"
    android:background="#d8e0d8">

<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:hint="Type something here"
        android:maxLines="2"/>

    <Button
        android:id="@+id/send"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Send"/>

</LinearLayout>

</LinearLayout> 

• 在主界面中放置的RecyclerView用于显示消息
• EditText用于编辑消息
• Button用于发送消息

定义消息的实体类Msg

package com.example.uibestpractice;

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 String getContent() {
        return content;
    }
    public int getType() {
        return type;
    }
}

• 用两个常量来表示消息的类型（接收的还是发送的）

编写RecyclerView的子布局（msg_item.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"
    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/message_left">

        <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/message_right">

        <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>

• 将接收的消息居左对齐，发送的消息居右对齐

创建RecyclerView适配器类

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;

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

    static class ViewHolder extends RecyclerView.ViewHolder {
        LinearLayout leftLayout;
        LinearLayout rightLayout;
        TextView leftMsg;
        TextView rihgtMsg;

        public ViewHolder(View view) {
            super(view);
            leftLayout = (LinearLayout) view.findViewById(R.id.left_layout);
            rightLayout = (LinearLayout) view.findViewById(R.id.right_layout);
            leftMsg = (TextView) view.findViewById(R.id.left_msg);
            rihgtMsg = (TextView) view.findViewById(R.id.right_msg);
        }
    }

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

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

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

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

• 定义了一个内部类ViewHolder，继承自RecyclerView.ViewHolder。ViewHolder的构造函数中传入一个View参数，这个参数通常是RecyclerView子项的最外层布局，这样我们就可以通过findViewById()方法来获取布局中的接收和发送消息布局的实例了。
• MsgAdapter中也有一个构造函数，将要展示的数据源传进来复制给mMsgList。
• MsgAdapter继承自RecyclerView.Adapter，必须重写onCreateViewHolder()、onBindViewHolder()、getItemCount()三个方法。
• onCreateViewHolder()用于创建ViewHolder实例，在这个方法中将msg_item布局加载进来，然后创建一个ViewHolder实例，并把加载出来的布局传到构造函数中，返回实例。
• onBindViewHolder()用于对RecyclerView子项的数据进行赋值。
• getItemCount()获得RecyclerView有多少个子项

使用RecyclerView（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);
        initMsgs();
        inputText = (EditText) findViewById(R.id.input_text);
        send = (Button) findViewById(R.id.send);
        msgRecyclerView = (RecyclerView) findViewById(R.id.msg_recycler_view);
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        msgRecyclerView.setLayoutManager(layoutManager);
        adapter = new MsgAdapter(msgList);
        msgRecyclerView.setAdapter(adapter);
        send.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String content = inputText.getText().toString();
                if (!"".equals(content)) {
                    Msg msg = new Msg(content,Msg.TYPE_SENT);
                    msgList.add(msg);
                    adapter.notifyItemInserted(msgList.size()-1);
                    msgRecyclerView.scrollToPosition(msgList.size()-1);
                    inputText.setText("");
                }
            }
        });
    }

    private void initMsgs() {
        Msg msg1 = new Msg("Hello",Msg.TYPE_RECEIVED);
        msgList.add(msg1);
        Msg msg2 = new Msg("I'm John",Msg.TYPE_RECEIVED);
        msgList.add(msg2);
        Msg msg3 = new Msg("Hello",Msg.TYPE_SENT);
        msgList.add(msg3);
    }
}

• onCreate()方法中先获得了RecyclerView的实例，然后创建了LinearLayoutManager对象，并把它设置到RecyclerView的实例中去。LayoutManager用于指定RecyclerView的布局方式，这里使用是线性布局的意思，可以实现ListView相同的效果。
• 设置了send按钮的响应事件，如果内容不为空则创建出一个新的Msg对象，并添加到msgList中去，之后调用了适配器的方法notifyItemInserted()来通知列表有新数据插入，这样新增的消息才能在RecyclerView中显示。接着调用RecyclerView的scrollToPosition()方法，将显示的数据定位到最后一行，最后清空输入栏。

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