Android APN数据库查询对比分析(APN案例)

// Framework简化的Loader线程切换逻辑
public class CursorLoader extends AsyncTaskLoader<Cursor> {
    @Override
    public Cursor loadInBackground() { // 在AsyncTask线程执行
        return getContext().getContentResolver().query(uri, ...);
    }
    @Override
    protected void onStartLoading() {
        forceLoad(); // 触发异步加载
    }
}

// 验证调用线程的测试代码
new Handler(Looper.getMainLooper()).post(() -> {
    // 在主线程执行查询
    Cursor cursor = getContentResolver().query(Carriers.CONTENT_URI, ...);
    Log.d("ThreadTest", "MainThread query: " + (Looper.myLooper() == Looper.getMainLooper()));
});
// 输出结果：ThreadTest: MainThread query: true

%% APN Settings界面数据加载时序图
sequenceDiagram
    participant User
    participant ApnSettingsActivity
    participant LoaderManager
    participant CursorLoader
    participant TelephonyProvider
    participant Database
    User->>ApnSettingsActivity: 启动APN设置界面
    activate ApnSettingsActivity
    ApnSettingsActivity->>LoaderManager: initLoader(APN_LOADER_ID)
    LoaderManager->>CursorLoader: 创建新Loader实例
    activate CursorLoader
    CursorLoader->>TelephonyProvider: 异步执行query()
    activate TelephonyProvider
    TelephonyProvider->>Database: 执行SQL查询
    activate Database
    Database-->>TelephonyProvider: 返回APN数据Cursor
    deactivate Database
    TelephonyProvider-->>CursorLoader: 返回查询结果
    deactivate TelephonyProvider
    CursorLoader-->>LoaderManager: 交付结果
    deactivate CursorLoader
    LoaderManager->>ApnSettingsActivity: onLoadFinished()
    ApnSettingsActivity->>ApnSettingsActivity: 更新UI列表
    deactivate ApnSettingsActivity
    Note right of CursorLoader: 关键路径说明<br/>1. CursorLoader自动处理后台线程<br/>2. 数据库查询在AsyncTask线程池执行<br/>3. 结果通过Handler返回主线程

package com.android.settings.network.apn;
// APN数据库查询不会阻塞主线程，通过CursorLoader机制实现
// 实际查询发生在AsyncTask线程（AsyncTask.THREAD_POOL_EXECUTOR）
// 结果回调通过Handler机制返回主线程
// ApnSettings.java 核心逻辑
public class ApnSettings extends PreferenceActivity implements LoaderManager.LoaderCallbacks<Cursor> {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        getLoaderManager().initLoader(APN_LOADER_ID, null, this); // 启动异步加载
    }
    @Override
    public Loader<Cursor> onCreateLoader(int id, Bundle args) {
        return new CursorLoader(this, Telephony.Carriers.CONTENT_URI,
                PROJECTION, null, null, Telephony.Carriers.DEFAULT_SORT_ORDER);
    }
    @Override
    public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
        mAdapter.swapCursor(data); // 主线程更新UI
    }
}
 

/** Handle each different apn setting. */
public class ApnSettings extends RestrictedSettingsFragment
        implements Preference.OnPreferenceChangeListener {
    static final String TAG = "ApnSettings";