Question

此处为MainActivity.java文件。我在notes.add(set);

中收到错误

package inandroid.jeetna.appnotes;

import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Set;

public class MainActivity extends AppCompatActivity {

    static ArrayList<String> notes = new ArrayList<>();
    static ArrayAdapter arrayAdapter;
    static Set<String> set;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });

        ListView listView = (ListView) findViewById(R.id.listView);

        SharedPreferences sharedPreferences = this.getSharedPreferences("inandroid.jeetna" +
                ".appnotes", Context.MODE_PRIVATE);

        set = sharedPreferences.getStringSet("notes", null);

        notes.clear();

        if(set!=null){
            notes.add(set);
        }else{
            notes.add("Testing data default note");
            set = new HashSet<String>();
            set.addAll(notes);
            sharedPreferences.edit().putStringSet("notes", set).apply();
        }

        arrayAdapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1,
                notes);
        listView.setAdapter(arrayAdapter);

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                Intent in = new Intent(getApplicationContext(), EditYourNote.class);
                in.putExtra("noteId", i);
                startActivity(in);
            }
        });




    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.add) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

这里的错误信息是：

Error:(55, 18) error: no suitable method found for add(Set<String>)
method ArrayList.add(int,String) is not applicable
(actual and formal argument lists differ in length)
method ArrayList.add(String) is not applicable
(actual argument Set<String> cannot be converted to String by method invocation conversion)
method AbstractList.add(String) is not applicable
(actual argument Set<String> cannot be converted to String by method invocation conversion)
method AbstractList.add(int,String) is not applicable
(actual and formal argument lists differ in length)
method AbstractCollection.add(String) is not applicable
(actual argument Set<String> cannot be converted to String by method invocation conversion)

Answer 1

使用notes.addAll(set)代替notes.add(set)。此方法适用于附加的集合。

Answer 2

使用此

 static ArrayList<Set<String>> notes = new ArrayList<>();

找不到合适的添加方法（Set <string>）

2 个答案: