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我正在尝试创建一个数据库。如何使用 disableWriteAheadLogging
在创建数据库之前？ ——
那么我相信你的问题是你没有授予所需的权限，即使你说你有：-
添加了读写权限。
您需要授予 WRITE_EXTERNAL_STORAGE（这隐式授予 READ_EXTERNAL_STORAGE）。
对于 API 23+ Android 6+ 而不是 9+ 的设备，这需要通过 MANIFEST 授予权限，例如:-
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
而且用户根据 Permission approval 授予访问权限。对于低于 API 23 的设备，仅需要清单权限。
示例
以下是一个简单的示例，它复制了问题并显示授予权限可以纠正问题。
- 清单包含上述 uses-permission 条目。
通过以下（ExternalStoragePermissions.java）重新获取用户权限：-
abstract class ExternalStoragePermissions {
private static final int REQUEST_EXTERNAL_STORAGE = 1;
private static String[] PERMISSIONS_STORAGE = {
Manifest.permission.WRITE_EXTERNAL_STORAGE
};
public ExternalStoragePermissions(Activity callingActivity) {}
// Note call this method
public static void verifyStoragePermissions(Activity activity) {
int permission = ActivityCompat.checkSelfPermission(
activity,
Manifest.permission.WRITE_EXTERNAL_STORAGE);
if(permission != PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(
activity,
PERMISSIONS_STORAGE,
REQUEST_EXTERNAL_STORAGE
);
}
}
}
使用的活动（MainActivity.java）是：-
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if(Build.VERSION.SDK_INT >= 23) {
ExternalStoragePermissions.verifyStoragePermissions(this);
}
SQLiteDatabase myDB = null;
myDB = this.openOrCreateDatabase("/sdcard/Download/2019-11-14 07-49-56 AM.db", MODE_PRIVATE, null);
DatabaseUtils.dumpCursor(
myDB.query("sqlite_master",null,null,null,null,null,null)
);
myDB.close();
}
}
结果
应用程序首次运行时显示：-
但是由于主线程继续并且访问权限尚未被授予，那么日志包括：-
2019-11-15 08:35:33.439 11874-11874/a.so58855993copyfromassets D/AndroidRuntime: Shutting down VM
2019-11-15 08:35:33.440 11874-11874/a.so58855993copyfromassets E/AndroidRuntime: FATAL EXCEPTION: main
Process: a.so58855993copyfromassets, PID: 11874
java.lang.RuntimeException: Unable to start activity ComponentInfo{a.so58855993copyfromassets/a.so58855993copyfromassets.MainActivity}: android.database.sqlite.SQLiteCantOpenDatabaseException: unknown error (code 14 SQLITE_CANTOPEN): Could not open database
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
Caused by: android.database.sqlite.SQLiteCantOpenDatabaseException: unknown error (code 14 SQLITE_CANTOPEN): Could not open database
at android.database.sqlite.SQLiteConnection.nativeOpen(Native Method)
at android.database.sqlite.SQLiteConnection.open(SQLiteConnection.java:215)
at android.database.sqlite.SQLiteConnection.open(SQLiteConnection.java:197)
at android.database.sqlite.SQLiteConnectionPool.openConnectionLocked(SQLiteConnectionPool.java:505)
at android.database.sqlite.SQLiteConnectionPool.open(SQLiteConnectionPool.java:206)
at android.database.sqlite.SQLiteConnectionPool.open(SQLiteConnectionPool.java:198)
at android.database.sqlite.SQLiteDatabase.openInner(SQLiteDatabase.java:915)
at android.database.sqlite.SQLiteDatabase.open(SQLiteDatabase.java:895)
at android.database.sqlite.SQLiteDatabase.openDatabase(SQLiteDatabase.java:786)
at android.app.ContextImpl.openOrCreateDatabase(ContextImpl.java:812)
at android.app.ContextImpl.openOrCreateDatabase(ContextImpl.java:797)
at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:310)
at a.so58855993copyfromassets.MainActivity.onCreate(MainActivity.java:27)
at android.app.Activity.performCreate(Activity.java:7802)
at android.app.Activity.performCreate(Activity.java:7791)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:214)
at android.app.ActivityThread.main(ActivityThread.java:7356)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
但是在此阶段，应用程序仍处于活动状态，因为请求权限的对话框仍处于活动状态。单击允许会导致应用程序崩溃，但随后会根据日志内容重新启动并成功创建数据库：-
2019-11-15 08:41:13.615 I/System.out: >>>>> Dumping cursor android.database.sqlite.SQLiteCursor@5df21a1
2019-11-15 08:41:13.616 I/System.out: 0 {
2019-11-15 08:41:13.616 I/System.out: type=table
2019-11-15 08:41:13.616 I/System.out: name=android_metadata
2019-11-15 08:41:13.616 I/System.out: tbl_name=android_metadata
2019-11-15 08:41:13.616 I/System.out: rootpage=3
2019-11-15 08:41:13.616 I/System.out: sql=CREATE TABLE android_metadata (locale TEXT)
2019-11-15 08:41:13.616 I/System.out: }
2019-11-15 08:41:13.616 I/System.out: <<<<<
- 注意以上只是一个演示。在要使用的应用程序中，您显然会在尝试访问数据库之前设置权限。
- 理想情况下，您不应硬编码路径，而应使用系统值，例如Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS) 获取路径。
- 通常，您会通过 Context 的 getDatabasePath 方法将数据库放置在应用程序的数据中，而不是将数据集放置在下载文件夹中。