书小宅之android——聊天界面的实现

制作Nine-Patch图片

说明：一种被特殊处理过的图片，指定哪些区域可以被拉伸，哪些区域不可以。
从android Studio2.3开始，不再单独提供draw9patch.bat文件，要生成Nine-Patch图片文件，则在res/drawable目录下添加.png格式的图片，并且将其命名改成bubble_right.9.png形式。

双击打开图片拖拉点限定拉伸区域。

在layout文件中写入如下句子测试拉伸效果：

android:background="@drawable/bubble_right"

添加库依赖

添加RecyclerView的库依赖的参考链接
RecyclerView用法参考
在SDK manager中添加库：

常见问题解决

1、若出现依赖包冲突问题：

All com.android.support libraries must use the exact same version specification (mixing versions can lead to runtime crashes). Found versions 27.1.1, 25.3.0. Examples include com.android.support:animated-vector-drawable:27.1.1 and com.android.support:design:25.3.0 less... (Ctrl+F1)
There are some combinations of libraries, or tools and libraries, that are incompatible, or can lead to bugs. One such incompatibility is compiling with a version of the Android support libraries that is not the latest version (or in particular, a version lower than your targetSdkVersion.)

按提示加入

//noinspection GradleCompatible

2、若出现Configuration ‘compile’ is obsolete and has been replaced with ‘implementation’ and ‘api’.的问题是因为有些配置过时，其解决方式如下：
compile 改成implementation
androidTestCompile改成androidTestImplementation
testCompile 改成testImplementation

3、若出现Failed to resolve: com.android.support:recyclerview-v7:28.0.0,提示migrate to androidX libraries问题：

这是因为添加了不存在的依赖
在build gradle中发现此时依赖中的编译版本和配置中的依赖版本不同：

修改其中的三句话重新编译即可

    compileSdkVersion 28targetSdkVersion 28

4、若出现闪退问题
教程上recyclerview写法如下，一直会出现闪退问题

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

如下修改代码，问题解决：

<androidx.recyclerview.widget.RecyclerViewandroid:id="@+id/msg_recycler_view"android:layout_width="match_parent"android:layout_height="0dp"android:layout_weight="1"/>

编写聊天界面

chat.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="#d8e0e8"><androidx.recyclerview.widget.RecyclerViewandroid:id="@+id/msg_recycler_view"android:layout_width="match_parent"android:layout_height="0dp"android:layout_weight="1"android:divider="#0000"/><LinearLayoutandroid:layout_width="match_parent"android:layout_height="wrap_content"><EditTextandroid: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" /><Buttonandroid:id="@+id/send"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="Send" /></LinearLayout></LinearLayout>

msg_item.xml

<?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"><LinearLayoutandroid:layout_width="wrap_content"android:layout_height="wrap_content"android:orientation="horizontal"><ImageViewandroid:id="@+id/head_left"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_gravity="left"android:src="@drawable/portrait1"/><LinearLayoutandroid:id="@+id/left_layout"android:layout_height="wrap_content"android:layout_width="wrap_content"android:layout_gravity="left"android:background="@drawable/bubble_left"><TextViewandroid: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><LinearLayoutandroid:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_gravity="right"android:orientation="horizontal"><LinearLayoutandroid:id="@+id/right_layout"android:layout_height="wrap_content"android:layout_width="wrap_content"android:layout_gravity="right"android:background="@drawable/bubble_right"><TextViewandroid:id="@+id/right_msg"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_gravity="center"android:layout_margin="10dp"/></LinearLayout><ImageViewandroid:id="@+id/head_right"android:layout_width="wrap_content"android:layout_height="wrap_content"android:src="@drawable/portrait2"/></LinearLayout></LinearLayout>

Msg类

package com.example.wechat;public class Msg {//收到的消息public static final int TYPE_RECEIVED = 0;//发送的消息public static final int TYPE_SEND=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;}
}

MsgAdapter类

package com.example.wechat;import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;
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;ImageView protrait1;ImageView protrait2;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);rightMsg=(TextView)view.findViewById(R.id.right_msg);protrait1=(ImageView)view.findViewById(R.id.head_right);protrait2=(ImageView)view.findViewById(R.id.head_left);}}public MsgAdapter(List<Msg> msgList){mMsgList=msgList;}@Overridepublic ViewHolder onCreateViewHolder(ViewGroup parent, int viewType){//onCreateViewHolder()用于创建ViewHolder实例View view= LayoutInflater.from(parent.getContext()).inflate(R.layout.msg_item,parent,false);return new ViewHolder(view);//把加载出来的布局传到构造函数中，再返回}@Overridepublic void onBindViewHolder(ViewHolder Holder,int position){//onBindViewHolder()用于对RecyclerView子项的数据进行赋值，会在每个子项被滚动到屏幕内的时候执行Msg msg=mMsgList.get(position);if(msg.getType()==Msg.TYPE_RECEIVED){//增加对消息类的判断，如果这条消息是收到的，显示左边布局，是发出的，显示右边布局Holder.leftLayout.setVisibility(View.VISIBLE);Holder.protrait2.setVisibility(View.VISIBLE);Holder.rightLayout.setVisibility(View.GONE);Holder.protrait1.setVisibility(View.GONE);Holder.leftMsg.setText(msg.getContent());}else if(msg.getType()==Msg.TYPE_SEND) {Holder.rightLayout.setVisibility(View.VISIBLE);Holder.protrait1.setVisibility(View.VISIBLE);Holder.leftLayout.setVisibility(View.GONE);Holder.protrait2.setVisibility(View.GONE);Holder.rightMsg.setText(msg.getContent());}}@Overridepublic int getItemCount(){return mMsgList.size();}
}

Main类

package com.example.wechat;import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;import java.util.ArrayList;
import java.util.List;public class Main extends AppCompatActivity {private List<Msg> msgList=new ArrayList<>();private EditText inputText;private Button send;private RecyclerView msgRecyclerView;private MsgAdapter adapter;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.chat);//初始化消息数据initMsgs();inputText=(EditText)findViewById(R.id.input_text);send=(Button)findViewById(R.id.send);msgRecyclerView=(RecyclerView)findViewById(R.id.msg_recycler_view);//LinearLayoutLayout即线性布局，创建对象后把它设置到RecyclerView当中LinearLayoutManager layoutManager=new LinearLayoutManager(this);msgRecyclerView.setLayoutManager(layoutManager);//创建MsgAdapter的实例并将数据传入到MsgAdapter的构造函数中adapter=new MsgAdapter(msgList);msgRecyclerView.setAdapter(adapter);//发送按钮点击事件send.setOnClickListener(new View.OnClickListener(){@Overridepublic void onClick(View v){//获取EditText中的内容String content=inputText.getText().toString();//内容不为空则创建一个新的Msg对象，并把它添加到msgList列表中if(!"".equals(content)){Msg msg=new Msg(content,Msg.TYPE_SEND);msgList.add(msg);//调用适配器的notifyItemInserted()用于通知列表有新的数据插入，这样新增的一条消息才能在RecyclerView中显示adapter.notifyItemInserted(msgList.size()-1);//调用scrollToPosition()方法将显示的数据定位到最后一行，以保证可以看到最后发出的一条消息msgRecyclerView.scrollToPosition(msgList.size()-1);//调用EditText的setText()方法将输入的内容清空inputText.setText("");}}});}private void initMsgs(){Msg msg1=new Msg("Hello guy.",Msg.TYPE_RECEIVED);msgList.add(msg1);Msg msg2=new Msg("Hello.Who is that?",Msg.TYPE_SEND);msgList.add(msg2);Msg msg3=new Msg("This is Tom!",Msg.TYPE_RECEIVED);msgList.add(msg3);}
}

效果演示