android实现简单的消息发送界面

通过这个小demo主要实现了一个发送消息的界面，该实例只有一个界面，发送方可以实现发送消息，我感觉主要的还是学习了一下消息框图片的缩放。

主要界面如上所示，下面看一下代码。

 代码主要有两个xml文件夹，两张修改过的照片，选中照片，右击再点击create 9 patch file 即可进行编辑，具体方法可以到网上搜索一下，还有3个java文件。

package com.example.sent_message;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.List;

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

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initMsgs();
        inputText = findViewById(R.id.input_text);
        sent = findViewById(R.id.btn_sent);
        msgRecyclerView = findViewById(R.id.msg_recycler_view);
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        msgRecyclerView.setLayoutManager(layoutManager);
        adapter = new MsgAdapter(msgList);
        msgRecyclerView.setAdapter(adapter);
        sent.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);
                    //提示有新消息，刷新recyclerView中的显示
                    adapter.notifyItemInserted(msgList.size()-1);
                    //定位至最后一行
                    msgRecyclerView.scrollToPosition(msgList.size() - 1);
                    //清空输入框里的内容
                    inputText.setText("");

                }
            }
        });

    }

    private void initMsgs() {
        Msg msg1 = new Msg("hello guy",Msg.TYPE_RECEIVED);
        msgList.add(msg1);
        Msg msg2 = new Msg("Hello , who is thst?",Msg.TYPE_SENT);
        msgList.add(msg2);
        Msg msg3 = new Msg("This is Tom,Nice talking to you！",Msg.TYPE_RECEIVED);
        msgList.add(msg3);
    }
}

package com.example.sent_message;

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;
    }
}

package com.example.sent_message;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

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 rightMsg;
        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            leftLayout = itemView.findViewById(R.id.left_layout);
            rightLayout = itemView.findViewById(R.id.right_layout);
            leftMsg = itemView.findViewById(R.id.left_msg);
            rightMsg = itemView.findViewById(R.id.right_msg);

        }
    }

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

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull 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(@NonNull ViewHolder holder, int position) {
        Msg msg = mMsgList.get(position);
        if(msg.getType() == Msg.TYPE_RECEIVED){
            //如果是收到的消息，则显示的是左边的布局，将右边的布局隐藏
            holder.leftLayout.setVisibility(View.VISIBLE);
            holder.rightLayout.setVisibility(View.GONE);
            holder.leftMsg.setText(msg.getContent());
        }else if(msg.getType() == Msg.TYPE_SENT){
            //发送的消息
            holder.rightLayout.setVisibility(View.VISIBLE);
            holder.leftLayout.setVisibility(View.GONE);
            holder.rightMsg.setText(msg.getContent());
        }
    }

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


}

<?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:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"

    tools:context=".MainActivity">

  <androidx.recyclerview.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/btn_sent"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="sent"/>
    </LinearLayout>

</LinearLayout>

<?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/msg_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/msg_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>