// Framework簡(jiǎn)化的Loader線程切換邏輯
public class CursorLoader extends AsyncTaskLoader<Cursor> {
    @Override
    public Cursor loadInBackground() { // 在AsyncTask線程執(zhí)行
        return getContext().getContentResolver().query(uri, ...);
    }
    @Override
    protected void onStartLoading() {
        forceLoad(); // 觸發(fā)異步加載
    }
}

// 驗(yàn)證調(diào)用線程的測(cè)試代碼
new Handler(Looper.getMainLooper()).post(() -> {
    // 在主線程執(zhí)行查詢
    Cursor cursor = getContentResolver().query(Carriers.CONTENT_URI, ...);
    Log.d("ThreadTest", "MainThread query: " + (Looper.myLooper() == Looper.getMainLooper()));
});
// 輸出結(jié)果：ThreadTest: MainThread query: true

%% APN Settings界面數(shù)據(jù)加載時(shí)序圖
sequenceDiagram
    participant User
    participant ApnSettingsActivity
    participant LoaderManager
    participant CursorLoader
    participant TelephonyProvider
    participant Database
    User->>ApnSettingsActivity: 啟動(dòng)APN設(shè)置界面
    activate ApnSettingsActivity
    ApnSettingsActivity->>LoaderManager: initLoader(APN_LOADER_ID)
    LoaderManager->>CursorLoader: 創(chuàng)建新Loader實(shí)例
    activate CursorLoader
    CursorLoader->>TelephonyProvider: 異步執(zhí)行query()
    activate TelephonyProvider
    TelephonyProvider->>Database: 執(zhí)行SQL查詢
    activate Database
    Database-->>TelephonyProvider: 返回APN數(shù)據(jù)Cursor
    deactivate Database
    TelephonyProvider-->>CursorLoader: 返回查詢結(jié)果
    deactivate TelephonyProvider
    CursorLoader-->>LoaderManager: 交付結(jié)果
    deactivate CursorLoader
    LoaderManager->>ApnSettingsActivity: onLoadFinished()
    ApnSettingsActivity->>ApnSettingsActivity: 更新UI列表
    deactivate ApnSettingsActivity
    Note right of CursorLoader: 關(guān)鍵路徑說明<br/>1. CursorLoader自動(dòng)處理后臺(tái)線程<br/>2. 數(shù)據(jù)庫(kù)查詢?cè)贏syncTask線程池執(zhí)行<br/>3. 結(jié)果通過Handler返回主線程

package com.android.settings.network.apn;
// APN數(shù)據(jù)庫(kù)查詢不會(huì)阻塞主線程，通過CursorLoader機(jī)制實(shí)現(xiàn)
// 實(shí)際查詢發(fā)生在AsyncTask線程（AsyncTask.THREAD_POOL_EXECUTOR）
// 結(jié)果回調(diào)通過Handler機(jī)制返回主線程
// ApnSettings.java 核心邏輯
public class ApnSettings extends PreferenceActivity implements LoaderManager.LoaderCallbacks<Cursor> {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        getLoaderManager().initLoader(APN_LOADER_ID, null, this); // 啟動(dòng)異步加載
    }
    @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); // 主線程更新UI
    }
}
 

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