为什么变量 len 值在数据库事务中没有改变？

Question

    //this is constructor of my code
    constructor(props) {
        super(props);
        this.state = {
        textValue:this.getFavoritesLength(),
        };
    }

//此 sqlite 代码 db.transaction 执行 prefect 但它不会更改 var len 的值它总是 returns 0 而我将 len 的值更改为 table 长度。

getFavoritesLength()
{
    var len = 0;
    db.transaction(tx => {
        tx.executeSql(
            'SELECT * FROM table_favorites', [],
            (tx, results) => {
                len = results.rows.length;
                console.log('select * results are = ', len);
                // if (len > 0) {
                //   return len;
                // }else{
                //   return 0;
                // }
            }
        );
    });
    return len;

}

Answer 1

虽然运行查询它不会立即提供响应。查询的执行需要一些时间，并在回调函数中给出响应。您可以尝试使用 async

insertarDatos = () => {
    return new Promise((resolve, reject) => {
      db.transaction((tx) => {
        try {
          /* Successful transaction */
          /* Make sure to call resolve when the transaction has finished, maybe 
             db.transaction has a success callback
          */
          resolve()
        } catch (error) {
          /* Failed transaction */
          // if you reject any eventual errors, you can catch them when calling the function insertarDatos

          reject(error)
        }
      });
    })
  }

为什么变量 len 值在数据库事务中没有改变？

Why variable len value not changing in db transaction?

javascript

android

ios

android-sqlite

react-native