使用 Kotlin 读取 Android SQLite 数据库时出错

Question

当运行下面的代码时，我收到错误消息：

java.lang.RuntimeException: Unable to start activity
 ComponentInfo{com.example.songapp/com.example.songapp.MainActivity}: java.io.FileNotFoundException:
 /data/data/com.example.songapp/databases/songs.db: open failed: ENOENT (No such file or directory)

报错的代码是这样的：

@Throws(IOException::class)
fun copyDataBase(context: Context, OUTPUT_DB_PATH: String, DB_NAME: String) {
    print("*** in copyDataBase ***")
    // Path to output database path (application database path).
    var APP_DB_FILE_PATH = OUTPUT_DB_PATH + "/" + DB_NAME

    // Path to input database file.
    var INPUT_DB_PATH = "database/" + DB_NAME

    // Open your local db as the input stream
    // This is how to get path from assets directory
    val databaseInput: InputStream = context.assets.open(INPUT_DB_PATH)

    // Open the empty db as the output stream
    val databaseOutput: OutputStream = FileOutputStream(APP_DB_FILE_PATH)

    // Transfer bytes from the inputfile to the outputfile
    val buffer = ByteArray(1024)
    var length: Int
    while (databaseInput.read(buffer).also { length = it } > 0) {
        databaseOutput.write(buffer, 0, length)
    }

    // Close the streams
    databaseOutput.flush()
    databaseOutput.close()
    databaseInput.close()
}

这在主 activity 中调用如下：

var DB_PATH = "/data/data/com.example.songapp/databases/"
var DB_NAME = "songs.db"

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        // Get context and supply it to the function
        // This is where error happens, by disabling this the app run successful.
        copyDataBase(this, DB_PATH, DB_NAME)

        setContent {
            Column() {
                TopAppBar(title = { Text(text = "Nyimbo") })
                ScrollableColumn(Modifier.fillMaxWidth()
                    .padding(10.dp)) {
                    lyricsPageComposable(lyricsMap = songMap)
                }
            }
        }
    }
}

我在资产目录 assets/database/songs.db 中有一个预填充的 SQLite 数据库，我希望将其复制到 /data/data/com.example.songapp/databases/songs.db 中。我不知道如何检查复制是否成功。我在这里错过了什么？我知道找不到数据库文件。是不是路径不对？难道是没有复制数据库？我怎么知道？我正在使用物理 Android phone 来测试应用程序。

Answer 1

When running the code below I get the error message

很可能，/data/data/com.example.songapp/databases/ 还不作为目录存在。

This is being called in the main activity as follows

请不要硬编码路径。您可以通过 calling getDatabasePath() on your Activity or other Context.

获取数据库的标准位置

I do not know how to check whether copying has succeeded

如果您使用的是 Android Studio，设备文件资源管理器工具默认停靠在右侧，可让您浏览设备的文件系统。

使用 Kotlin 读取 Android SQLite 数据库时出错

Error reading Android SQLite database using Kotlin

android

kotlin

android-sqlite

android-jetpack