如何在Android Studio中结合SQLite与Picasso实现GridView图片加载

我来帮你搞定用Picasso加载SQLite里的图片URL到GridView的问题，一步步来，很清晰的：

1. 先定义历史记录实体类 #

创建一个History类来封装每条记录的用户名和图片URL，方便后续数据传递和处理：

public class History {
    private String username;
    private String imageUrl;

    public History(String username, String imageUrl) {
        this.username = username;
        this.imageUrl = imageUrl;
    }

    // Getter方法，供Adapter获取数据
    public String getUsername() {
        return username;
    }

    public String getImageUrl() {
        return imageUrl;
    }
}

2. 完善SQLite数据库操作 #

确保你的Database类能正确插入、查询并返回List<History>类型的历史数据，避免直接返回原始Cursor：

public class Database extends SQLiteOpenHelper {
    // 常量定义，方便维护
    private static final String DB_NAME = "SearchHistory.db";
    private static final int DB_VERSION = 1;
    private static final String TABLE_HISTORY = "history";
    private static final String COLUMN_USERNAME = "username";
    private static final String COLUMN_IMAGE_URL = "image_url";

    public Database(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // 创建历史记录表，用username作为主键避免重复
        String createTable = "CREATE TABLE " + TABLE_HISTORY + " ("
                + COLUMN_USERNAME + " TEXT PRIMARY KEY,"
                + COLUMN_IMAGE_URL + " TEXT)";
        db.execSQL(createTable);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_HISTORY);
        onCreate(db);
    }

    // 插入/更新历史记录（replace会自动覆盖重复的username）
    public void insertOrUpdateHistory(String username, String imageUrl) {
        SQLiteDatabase db = getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(COLUMN_USERNAME, username);
        values.put(COLUMN_IMAGE_URL, imageUrl);
        db.replace(TABLE_HISTORY, null, values);
        db.close();
    }

    // 查询所有历史记录，返回封装好的List<History>
    public List<History> History_list() {
        List<History> historyList = new ArrayList<>();
        SQLiteDatabase db = getReadableDatabase();
        Cursor cursor = db.rawQuery("SELECT * FROM " + TABLE_HISTORY, null);

        if (cursor.moveToFirst()) {
            do {
                String username = cursor.getString(cursor.getColumnIndexOrThrow(COLUMN_USERNAME));
                String imageUrl = cursor.getString(cursor.getColumnIndexOrThrow(COLUMN_IMAGE_URL));
                historyList.add(new History(username, imageUrl));
            } while (cursor.moveToNext());
        }
        cursor.close();
        db.close();
        return historyList;
    }
}

3. 为GridView创建自定义Adapter（核心步骤） #

这一步是实现Picasso加载图片的关键，在Adapter的getView方法中调用Picasso加载图片URL：

public class HistoryAdapter extends BaseAdapter {
    private Context context;
    private List<History> historyList;

    public HistoryAdapter(Context context, List<History> historyList) {
        this.context = context;
        this.historyList = historyList;
    }

    @Override
    public int getCount() {
        return historyList.size();
    }

    @Override
    public Object getItem(int position) {
        return historyList.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder;
        // 复用View优化性能
        if (convertView == null) {
            convertView = LayoutInflater.from(context).inflate(R.layout.history_item, parent, false);
            holder = new ViewHolder();
            holder.avatarIv = convertView.findViewById(R.id.iv_avatar);
            holder.usernameTv = convertView.findViewById(R.id.tv_username);
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }

        History currentHistory = historyList.get(position);
        // 设置用户名
        holder.usernameTv.setText(currentHistory.getUsername());
        // 用Picasso加载图片到ImageView
        Picasso.get()
                .load(currentHistory.getImageUrl())
                .placeholder(R.drawable.default_avatar) // 加载中的占位图
                .error(R.drawable.error_avatar) // 加载失败的占位图
                .centerCrop()
                .into(holder.avatarIv);

        return convertView;
    }

    // ViewHolder类，避免重复findViewById
    private static class ViewHolder {
        ImageView avatarIv;
        TextView usernameTv;
    }
}

对应的history_item.xml布局示例（你可以根据需求调整样式）：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="10dp">

    <ImageView
        android:id="@+id/iv_avatar"
        android:layout_width="70dp"
        android:layout_height="70dp"
        android:scaleType="centerCrop"
        android:background="@drawable/avatar_round" />

    <TextView
        android:id="@+id/tv_username"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="5dp"
        android:textSize="13sp"
        android:textColor="@color/black" />
</LinearLayout>

4. 在MainActivity中绑定数据到GridView #

在onResume方法中获取历史数据，初始化Adapter并设置给GridView：

public class MainActivity extends AppCompatActivity {
    private GridView historyGridView;
    private HistoryAdapter historyAdapter;
    private List<History> historyList;

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

        // 初始化GridView
        historyGridView = findViewById(R.id.grid_view_history);
    }

    @Override
    protected void onResume() {
        super.onResume();
        Database db = new Database(getApplicationContext());
        historyList = db.History_list();

        if (historyList.isEmpty()) {
            // 没有历史记录时的处理，比如显示空状态提示
            ImageButton timerBtn = findViewById(R.id.users_history_timer);
            // 这里可以添加隐藏GridView、显示空布局的逻辑
        } else {
            // 初始化Adapter并绑定到GridView
            historyAdapter = new HistoryAdapter(this, historyList);
            historyGridView.setAdapter(historyAdapter);
        }
    }

    // 用户搜索完成后调用此方法保存历史记录
    private void saveSearchHistory(String username, String imageUrl) {
        Database db = new Database(getApplicationContext());
        db.insertOrUpdateHistory(username, imageUrl);
        // 保存后刷新列表
        historyList = db.History_list();
        if (historyAdapter != null) {
            historyAdapter.notifyDataSetChanged();
        }
    }
}

5. 检查必要配置 #

• 添加Picasso依赖：在app/build.gradle（Module级别）的dependencies中加入：

  implementation 'com.squareup.picasso:picasso:2.71828'
  

• 网络权限：如果图片URL是网络地址，需要在AndroidManifest.xml中添加：

  <uses-permission android:name="android.permission.INTERNET" />
  

内容的提问来源于stack exchange，提问作者user8143839