java - 从另一个 Activity 中单击按钮时从 Activity 中删除 ListView 项目

Question

我有一个 MainActivity，它显示一个 listview 以及我动态添加到其中的项目。到目前为止一切正常。现在想要创建一个按钮来删除被单击的listview项目。这是我附带的代码。

主要 Activity

package news;

import android.app.Activity;
import android.content.Intent;
import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {
    ArrayAdapter<String> newslist_adapter;
    ArrayList<String> new_subject = new ArrayList<>();
    ArrayList<String> new_post = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final ListView post_view = findViewById(R.id.news_feed);

        FloatingActionButton add_post_button = findViewById(R.id.post_btn);

        //create click event and pass values of arrays
        post_view.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int position, long id) {
                Intent intent = new Intent(getApplicationContext(), full_post_activity.class);
                intent.putExtra("Subject", new_subject);
                intent.putExtra("Post", new_post);
                intent.putExtra("position", id);
//                getApplicationContext().startActivity(intent);
                startActivityForResult(intent, 2);
            }
        });

        //create button connection and create keylistener
        add_post_button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(MainActivity.this, addpost_activity.class);
                startActivityForResult(intent, 1);

            }
        });

    }
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        final ListView post_view = findViewById(R.id.news_feed);
        if (requestCode == 1) {
            if(resultCode == Activity.RESULT_OK){
                //get subject and post from second activity
                String new_subject_value = data.getStringExtra("newSubject");
                String new_post_value = data.getStringExtra("newPost");
                new_subject.add(new_subject_value);
                new_post.add(new_post_value);
                newslist_adapter = new ArrayAdapter<>(
                        MainActivity.this,
                        android.R.layout.simple_expandable_list_item_1, new_subject);
                post_view.setAdapter(newslist_adapter);

            }
        }
        if (requestCode == 2) {
            if(resultCode == Activity.RESULT_OK){
                String item2delete = data.getStringExtra("id");
                new_subject.remove(item2delete);
                newslist_adapter = new ArrayAdapter<>(
                        MainActivity.this,
                        android.R.layout.simple_expandable_list_item_1, new_subject);
                post_view.setAdapter(newslist_adapter);
            }
        }
    }
} 

第二个 Activity

package news;

import android.app.Activity;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import java.util.ArrayList;

public class full_post_activity extends AppCompatActivity {

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

        final int id = getIntent().getExtras().getInt("id");

        //create view reference
        final TextView subject_edit = findViewById(R.id.subject_input);
        final TextView post_edit = findViewById(R.id.post_input);

        //create button reference
        Button delete_button = findViewById(R.id.full_post_delete_btn);

        //create click event
        delete_button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(getApplicationContext(), MainActivity.class);
                intent.putExtra("id", id);
                setResult(Activity.RESULT_OK, intent);
                finish();
            }
        });

        ArrayList<String> subject_array = (ArrayList<String>) getIntent().getSerializableExtra("Subject");
        ArrayList<String> post_array = (ArrayList<String>) getIntent().getSerializableExtra("Post");

        String subject_string = subject_array.get(0);
        String post_string = post_array.get(0);

        //set textview text
        subject_edit.setText(subject_string);
        post_edit.setText(post_string);
    }
}

我现在的问题是，删除按钮除了返回到MainActivity之外没有执行任何操作。我做错了什么？

Answer 1

您无法获取 MainActivity 的 id 值。第二个 Activity 中的这一行导致问题

final int id = getIntent().getExtras().getInt("id");

在主 Activity 中，您可以使用名称索引“位置”放置 id 值

intent.putExtra("position", id);

所以你应该将它们更改为

在第二个 Activity 中

final int id = getIntent().getExtras().getInt("position");

或主要 Activity

intent.putExtra("id", id);

已更新，请在主要 Activity 中尝试此操作

intent.putExtra("id", position);