模拟微信发信息的界面,设置一个发送按钮.点击按钮后发送一条信息,但是退出聊天界面后再重新进去,所有item都消失了,如何实现保存这些item

1.Adapter

public class MsgTalkAdapter extends BaseAdapter {
private LinkedList<MessageEntity>mData;
private Context context;
public MsgTalkAdapter(LinkedList<MessageEntity> mData, Context context){
    this.mData=mData;
    this.context=context;
}

    @Override
    public int getCount() {

    return mData.size();
    }


    @Override
    public Object getItem(int position) {
        return null;
    }


    @Override
    public long getItemId(int position) {

    return position;
    }


    @SuppressLint("ViewHolder")
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
    ViewHolder holder=null;
    if (convertView==null){
        convertView= LayoutInflater.from(context).inflate(R.layout.msg_item_right,parent,false);
        holder= new ViewHolder();
        holder.message=(TextView) convertView.findViewById(R.id.right_msg);
        convertView.setTag(holder);//将holder存储到convertView中

    }else {
        holder=(ViewHolder) convertView.getTag();
    }
    holder.message.setText(mData.get(position).getMessage());
return convertView;
    }

   static class ViewHolder{
     TextView message;
    }
    public  void  add(MessageEntity data){
     if (mData==null){
         mData=new LinkedList<>();

     }
     mData.add(data);
     notifyDataSetChanged();
    }
}

2.MessageEntity(目前只用了getMessage这个方法)

public class MessageEntity {
    private String name;
    private String message;
    private String date;
    private boolean isComeMsg=true;
    private boolean GetMsgType=true;

    public boolean GetMsgType() {
        return GetMsgType;
    }

    public void GetMsgType(boolean getMsgType) {
        GetMsgType = getMsgType;
    }

    public MessageEntity() {
    }

    public MessageEntity(String message) {
        this.message = message;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    public String getDate() {
        return date;
    }

    public void setDate(String date) {
        this.date = date;
    }

    public boolean isComeMsg() {
        return isComeMsg;
    }

    public void setComeMsg(boolean comeMsg) {
        isComeMsg = comeMsg;
    }
}

3.主类

public class fragmentActivity extends AppCompatActivity {

    private static final String TAG = "fragmentActivity";
    private ChoiceFragment choiceFragment;
    private SendMsgFragment sendMsgFragment;
    private ImageButton add;
    private ImageView backImageview;
    private EditText editTextmessage;
    private TextView textSendmessage;
    private TextView nameTextview;

    private ListView messageListview;
    private TextView userName;
private List<MessageEntity>mData=null;
private ArrayAdapter arrayAdapter;
    private Button send_btn;
    private String content;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.fragment_container);
        findFragment();
        initview();
        setName();
        ChangeFragment();
        MessageTalkView();
    }

    private void MessageTalkView() {
                MsgTalkAdapter msgTalkAdapter = new MsgTalkAdapter((LinkedList<MessageEntity>) mData,fragmentActivity.this);
        send_btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
        content = editTextmessage.getText().toString();
                Log.d(TAG,"CONTENT----"+content);
                switch (v.getId()){
                    case R.id.send_btn:
                        msgTalkAdapter.add(new MessageEntity(content));
                        break;
                }

              //  mData=new LinkedList<MessageEntity>();
               // mData.add(new MessageEntity(content));

        //SimpleAdapter simpleAdapter = new SimpleAdapter(fragmentActivity.this,getdata(),R.layout.msg_item_right,new String[]{"content"},new int[]{R.id.right_msg});
      //  messageListview.setAdapter(simpleAdapter);
       // simpleAdapter.notifyDataSetChanged();
                messageListview.setAdapter(msgTalkAdapter);
                msgTalkAdapter.notifyDataSetChanged();
                editTextmessage.setText("");
            }
        });

        }
    private List<Map<String,Object>> getdata() {
             Log.d(TAG,"CONTENT---"+content);
        List<Map<String,Object>>list= new ArrayList<>();
        Map map = new HashMap();
        map.put("content",content);
        list.add(map);
        return list;
    }

    private void setName() {
        Intent intent =getIntent();
        String name = intent.getStringExtra("username");
        Log.d(TAG,"NAME-----"+name);
        userName.setText(name);
    }

    void initview() {
         userName = findViewById(R.id.user_name);
         editTextmessage =(EditText)findViewById(R.id.msg_edit_text);
         backImageview =(ImageView) findViewById(R.id.back_btn);
         messageListview=(ListView)findViewById(R.id.message_list);
        send_btn = findViewById(R.id.send_btn);
        add = this.findViewById(R.id.add_view_action);


    }

    private void ChangeFragment() {
      add.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View v) {
              FragmentManager fm =getSupportFragmentManager();
              FragmentTransaction ft= fm.beginTransaction();
              ft.add(R.id.action_view,choiceFragment);
              ft.show(choiceFragment);
              ft.addToBackStack(null);
              ft.commit();
          }
      });
    }
    private void findFragment() {
        choiceFragment = new ChoiceFragment();
        sendMsgFragment = new SendMsgFragment();
    }
}