Question

我有这段代码。问题出在函数中，我试图在外部范围中分配给db var，但最终被声明为局部变量。

    <?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MechanicMore.MechanicHourlyRateActivity">

    <TextView
        android:id="@+id/HourlyText"
        android:layout_width="359dp"
        android:layout_height="28dp"
        android:layout_marginEnd="25dp"
        android:text="What is your hourly Rate?"
        android:textColor="@android:color/black"
        android:textSize="18sp"
        android:textStyle="bold"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <android.support.design.widget.TextInputLayout
        android:id="@+id/textInputLayout2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="25dp"
        android:layout_marginBottom="356dp"
        android:hint="Per Hour"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/HourlyText">

        <EditText
            android:id="@+id/mechanic_hourlyRate"
            android:layout_width="173dp"
            android:layout_height="86dp"
            android:layout_marginStart="8dp"
            android:layout_marginTop="8dp"
            android:layout_marginEnd="8dp"
            android:layout_marginBottom="8dp"
            android:digits="0123456789."
            android:ems="10"
            android:hint="Per Hour"
            android:inputType="numberDecimal" />
    </android.support.design.widget.TextInputLayout>

    </android.support.constraint.ConstraintLayout>

关于这一行，我的问题是：

var db *sqlx.DB

func GetDatabaseConnection() *sqlx.DB {

    if db == nil {

        db, err := sqlx.Connect("postgres", "user=foo dbname=bar sslmode=disable")
        if err != nil {
            log.Fatalln(err)
        }

    }

    return db
}

如何将db, err := sqlx.Connect(...)分配给外部范围，而不将其声明为局部变量？

Answer 1

var db *sqlx.DB

func GetDatabaseConnection() *sqlx.DB {

    if db == nil {
        var err error # ADD THIS LINE, AND DO = INSTEAD OF := ON NEXT LINE
        db, err = sqlx.Connect("postgres", "user=foo dbname=bar sslmode=disable")
        if err != nil {
            log.Fatalln(err)
        }

    }

    return db
}

将本地结果分配给外部范围

1 个答案: