如何使用SharedPreference中的Chat保存ListView

Question

我正在做一个Chat with bubble，其对话框为saved in a ListView，运行正常，现在我想save this Chat in memory，当我重新打开应用程序时，我可以跟踪对话， similar to WhatsApp。有人可以告诉我是否可以使用SharePreference来完成此操作吗？

以下是MainActivity代码：

public class MainActivity extends AppCompatActivity {
private ListView listView;
private View btnSend;
private EditText editText;
boolean myMessage = true;
private List<ChatBubble> ChatBubbles;
private ArrayAdapter<ChatBubble> adapter;

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

    ChatBubbles = new ArrayList<>();

    listView = (ListView) findViewById(R.id.list_msg);
    btnSend = findViewById(R.id.btn_chat_send);
    editText = (EditText) findViewById(R.id.msg_type);
    adapter = new MessageAdapter(this, R.layout.left_chat_bubble, ChatBubbles);
    listView.setAdapter(adapter);

    btnSend.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if (editText.getText().toString().trim().equals("")) {
                Toast.makeText(MainActivity.this, "Please input some text...", Toast.LENGTH_SHORT).show();
            } else {
                //add message to list
                ChatBubble ChatBubble = new ChatBubble(editText.getText().toString(), myMessage);
                ChatBubbles.add(ChatBubble);
                adapter.notifyDataSetChanged();
                editText.setText("");
                if (myMessage) {
                    myMessage = false;
                } else {
                    myMessage = true;
                }
            }
        }
    });
  }
}

以下错误：

Answer 1

您可以使用Gson：implementation 'com.google.code.gson:gson:2.8.5'

例如

Gson gson = new Gson();
String json = gson.toJson(ChatBubble);
mSharedPref.putString("chatList", json);
mSharedPref.apply();

然后检索它：

Gson gson = new Gson();
ArrayList<ChatBubble> mList = ArrayList<ChatBubble>();
String json = mSharedPref.getString("chatList", "");    
mList = gson.fromJson(json, ArrayList<ChatBubble>.class);

另一种方法是在您的类上实现Serializable，然后只需添加getString和putExtra

而不是getExtra

要创建SharedPreferences

SharedPreferences mSharedPref = PreferenceManager.getDefaultSharedPreferences(this);

SharedPreferences.Editor editor = mSharedPref.edit();
editor.putString()... 

编辑

创建如下的arrayList

ArrayList<ChatBubble> mList = new ArrayList<ChatBubble>();

您必须将列表存储在例如onDestroy（）或onStop（）

中

private void saveChat(){
SharedPreferences mSharedPref = PreferenceManager.getDefaultSharedPreferences(this);
SharedPreferences.Editor editor = mSharedPref.edit();
Gson gson = new Gson();
String json = gson.toJson(ChatBubble);
editor.putString("chatList", json);
editor.apply();
}

然后每次您在onCreate（）方法中进入MainActivity时

private void setUpChat(){
    SharedPreferences mSharedPref = PreferenceManager.getDefaultSharedPreferences(this);
    Gson gson = new Gson();
    String json = mSharedPref.getString("chatList", ""); 
    ChatBubble[] mArray = gson.fromJson(json,ChatBubble[].class)   
    mList = new ArrayList<>(Arrays.asList(mArray));
    adapter = new MessageAdapter(this, R.layout.left_chat_bubble, mList);
    listView.setAdapter(adapter);
}