使用 SharedPreferences 从另一个 activity 添加项目到 ArrayListAdapter

Question

我想将一些元素从 MainActivity 添加到另一个 activity，其中我有一个 arrayList 但我的问题是，当我插入一些东西时，交易就完成了，但是仅添加 1 个元素。我想向 arrayList 添加多个元素。在 MainActivity 中，我有 2 个 EditText 和 2 个 buttons（保存和 GoToNextActivity，我在其中放置了从 MainActivity 到 [=29= 的过渡意图]) 当我按下保存按钮时，如何向列表中添加更多元素？

public class items {

private String username;
private String password;

items(String user,String parola){
    username=user;
    password=parola;
}

public String getPassword() {
    return password;
}

public String getUsername() {
    return username;
}
}


public class itemsAdapter extends ArrayAdapter<items> {

private static final String LOG_TAG = itemsAdapter.class.getSimpleName();

public itemsAdapter(Activity context, ArrayList<items> item) {
    super(context, 0,item);
}

public View getView(int position, View convertView, ViewGroup parent){

    View listItemView = convertView;
    if (listItemView == null) {
        listItemView = LayoutInflater.from(getContext()).inflate(R.layout.list_items, parent, false);
    }

    items curentItems=getItem(position);

    TextView user=(TextView)listItemView.findViewById(R.id.list_user);
    TextView password=(TextView)listItemView.findViewById(R.id.list_password);

    user.setText(curentItems.getUsername());
    password.setText(curentItems.getPassword());


    return listItemView;
}
}

public class 列表扩展 AppCompatActivity {

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

    SharedPreferences sharedPreferences= getSharedPreferences("user", Context.MODE_PRIVATE);
    String name=sharedPreferences.getString("username","");
    String password=sharedPreferences.getString("password","");

    final ArrayList<items> login = new ArrayList<items>();
    login.add(new items(name,password));

    itemsAdapter itemsAdapter=new itemsAdapter(this,login);

    ListView listView = (ListView) findViewById(R.id.list_activity_container);
    listView.setAdapter(itemsAdapter);

}
}

public class MainActivity 扩展 AppCompatActivity {

EditText username;
EditText password;
TextView show;
Button save;
Button display;
Button go;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    username=(EditText)findViewById(R.id.username);
    password=(EditText)findViewById(R.id.password);
    show=(TextView)findViewById(R.id.show);
    save=(Button)findViewById(R.id.save);
    display=(Button)findViewById(R.id.displayInfo);
    go=(Button)findViewById(R.id.goToList);

    save.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            SharedPreferences sharedPreferences= getSharedPreferences("user", Context.MODE_PRIVATE);
            SharedPreferences.Editor editor=sharedPreferences.edit();

            editor.putString("username",username.getText().toString());
            editor.putString("password",password.getText().toString());
            editor.apply();

          //  Toast.makeText(this,"Saved",Toast.LENGTH_LONG).show();
        }
    });

    display.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            SharedPreferences sharedPreferences= getSharedPreferences("user", Context.MODE_PRIVATE);
            String name=sharedPreferences.getString("username","");
            String password=sharedPreferences.getString("password","");
            show.setText(name+"  "+password);
        }
    });

    go.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent=new Intent(MainActivity.this,list.class);
            startActivity(intent);
        }
    });
}
}

Answer 1

Shared Preferences 保存一个 键值对 。要在 SharedPreferences 中保存多个元素，您需要为每个元素分配一个唯一的键。让我们将密钥命名为 "userID".

int userID = 0;

and save user details to shared preferences like this

 SharedPreferences sharedPreferences= getSharedPreferences("user", Context.MODE_PRIVATE);
        SharedPreferences.Editor editor=sharedPreferences.edit();

        editor.putString("username_"+userID,username.getText().toString());
        editor.putString("password_"+userID,password.getText().toString());
        editor.apply();

添加另一个用户对象时，递增 userID

++userID;

现在您的 shared preferences 将包含两个具有键 <username_0> 和 <username_1> 的元素。

此外，在从 preferences 获取数据时，不要忘记使用正确的密钥。

String name=sharedPreferences.getString("username_"+userID,"");

For 循环：假设你有 5 个元素，你想将它们添加到你的 List

in onCreate of MainActivity.

 final ArrayList<items> login = new ArrayList<items>(itemCount);
    for (int i = 0; i < 5; i++) {
        // command below will be executed 5 times, and i will range from 0 to 4(both inclusive)
        login.add(new items("name" + i, "password" + i));
    }
    // now our login list has 5 elements(namely name0,name1...name4)

In click listener of save button, save entire list to shared preferences

save.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            SharedPreferences sharedPreferences = getSharedPreferences("user", Context.MODE_PRIVATE);
            SharedPreferences.Editor editor = sharedPreferences.edit();

            for (int i = 0; i < 5; i++) {
                // save entire list using loop.
                editor.putString("username" + i, login.get(i).getUsername());
                editor.putString("password" + i, login.get(i).getPassword());
            }
            editor.apply();

            //  Toast.makeText(this,"Saved",Toast.LENGTH_LONG).show();
        }
    });

in List activity , read data from preferences.

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

    final ArrayList<items> login = new ArrayList<items>();

    SharedPreferences sharedPreferences = getSharedPreferences("user", Context.MODE_PRIVATE);
    for (int i = 0; i < 5; i++) {
        String name = sharedPreferences.getString("username" + i, "");
        String password = sharedPreferences.getString("password" + i, "");

        login.add(new items(name, password));
    }

    itemsAdapter itemsAdapter = new itemsAdapter(this, login);

    ListView listView = (ListView) findViewById(R.id.list_activity_container);
    listView.setAdapter(itemsAdapter);

}

然而，在 ListActivity 中，您不需要从 shared preferences 中读取数据，您可以将数据捆绑在用于启动 ListActivity 的 Intent 中，并在 ListActivity 从 Intent 获取数据。

使用 SharedPreferences 从另一个 activity 添加项目到 ArrayListAdapter

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