android Listview模拟聊天界面

package com.example.test;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import java.util.ArrayList;

import static com.example.test.R.id.tv_receive;
import static com.example.test.R.id.tv_send;

public class MainActivity extends AppCompatActivity {


  private ArrayList<Msg> msgs;
  private EditText et_input;
  private MyAdapter myAdapter;
  private ListView lv;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    lv = (ListView) findViewById(R.id.lv);
    et_input = (EditText) findViewById(R.id.et_input);

    findViewById(R.id.bt_send).setOnClickListener(new View.OnClickListener() {
      @Override
      public void onClick(View v) {
        String content = et_input.getText().toString();
        if (!content.isEmpty()) {
          msgs.add(new Msg(content, Msg.TYPE_SEND));
          myAdapter.notifyDataSetChanged();
          lv.setSelection(msgs.size() - 1);
          et_input.setText("");
        } else {
          Toast.makeText(MainActivity.this, "请输入内容!", Toast.LENGTH_SHORT).show();
        }
      }
    });

    msgs = new ArrayList<>();
    msgs.add(new Msg("hello", Msg.TYPE_RECEIVE));
    msgs.add(new Msg("who is that?", Msg.TYPE_SEND));
    msgs.add(new Msg("this is LiLei,nice to meet you!", Msg.TYPE_RECEIVE));

    myAdapter = new MyAdapter();
    lv.setAdapter(myAdapter);

  }

  private class MyAdapter extends BaseAdapter {

    @Override
    public int getCount() {
      return msgs.size();
    }

    @Override
    public Msg getItem(int position) {
      return msgs.get(position);
    }

    @Override
    public long getItemId(int position) {
      return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
      ViewHolder holder;
      if (convertView == null) {
        holder = new ViewHolder();
        convertView = View.inflate(getApplicationContext(), R.layout.listview_item, null);
        holder.tv_receive = (TextView) convertView.findViewById(tv_receive);
        holder.tv_send = (TextView) convertView.findViewById(tv_send);
        convertView.setTag(holder);
      } else {
        holder = (ViewHolder) convertView.getTag();
      }
      Msg msg = getItem(position);
      if (msg.type == Msg.TYPE_RECEIVE) {
        holder.tv_receive.setVisibility(View.VISIBLE);
        holder.tv_send.setVisibility(View.GONE);
        holder.tv_receive.setText(msg.content);
      } else if (msg.type == Msg.TYPE_SEND) {
        holder.tv_send.setVisibility(View.VISIBLE);
        holder.tv_receive.setVisibility(View.GONE);
        holder.tv_send.setText(msg.content);
      }
      return convertView;
    }
  }

  private static class ViewHolder {
    TextView tv_receive;
    TextView tv_send;
  }
}

package com.example.test;

/**
 * Created by My on 2017/3/3.
 */
class Msg {
  static final int TYPE_RECEIVE = 1;
  static final int TYPE_SEND = 2;
  String content;
  int type;

  Msg(String content, int type) {
    this.content = content;
    this.type = type;
  }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:id="@+id/activity_main"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:background="#ccc"
  android:orientation="vertical"
  tools:context="com.example.test.MainActivity">

  <ListView
    android:id="@+id/lv"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_weight="1"
    android:divider="@null" />

  <LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <EditText
      android:id="@+id/et_input"
      android:layout_width="0dp"
      android:layout_height="wrap_content"
      android:layout_weight="1"
      android:hint="请输入要发送的内容" />

    <Button
      android:id="@+id/bt_send"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="发送" />
  </LinearLayout>
</LinearLayout>

<?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">

  <TextView
    android:id="@+id/tv_receive"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="start"
    android:background="@drawable/message_left"
    android:gravity="center"
    android:text="who?"
    android:textSize="20sp" />

  <TextView
    android:id="@+id/tv_send"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="end"
    android:background="@drawable/message_right"
    android:gravity="center"
    android:text="i am your father"
    android:textSize="20sp" />


</LinearLayout>