Kotlin:Java Util日期转换为字符串以进行数据绑定 [英] Kotlin: Java Util Date to String for Databindings

问题描述

我想通过数据绑定在视图中使用我的数据类的日期值. 如果我在Date字段上使用toString()方法，它将起作用.但是我想自定义日期值. 因此，我使用Method创建了Utils对象.这是Util对象

I want to use the Date value of my Data class in view via Databinding. If I use the toString() method on the Date field it works. But I want to customize the Date value. So I created the Utils object with Method. This is the Util object

object DateUtils {

     fun toSimpleString(date: Date) : String {
        val format = SimpleDateFormat("dd/MM/yyy")
        return format.format(date)
    }
}

但是如果我想像这样在xml中使用此方法

But if I want to use this method in the xml like this

<data>
    <import type="de.mjkd.journeylogger.Utils.DateUtils"/>

    <variable
        name="journey"
        type="de.mjkd.journeylogger.data.Journey"/>
</data>
...
    android:text="@{DateUtils.toSimpleString(journey.date)}"

我收到错误cannot find method toSimpleString(java.util.Date) in class ...

这是我的数据类:

data class Journey(var title: String, var date: Date?, var destination: String)

此代码有什么问题?

推荐答案

使用kotlin中的保留字 object ，您真正要做的就是声明一个实例. Java中的等效项或多或少类似于:

Using the reserved word object in kotlin, that you really doing is declare a single instance. the equivalent in java is something more or less like:

class DataUtils {
    static DataUtils INSTANCE;
    public String toSimpleString()...
}

然后在您调用它时执行DateUtils.INSTANCE.toSimpleString()

then when you call it you do a DateUtils.INSTANCE.toSimpleString()

您应该能够在xml中使用DateUtils.INSTANCE.toSimpleString()

You should capable to use DateUtils.INSTANCE.toSimpleString() in your xml

为了使toSimpleString可从静态上下文访问，您必须使用@JvmStatic

In order to make toSimpleString accessible from static context, you have to flag the method with@JvmStatic

object DateUtils {
    @JvmStatic
    fun toSimpleString(date: Date) : String {
        val format = SimpleDateFormat("dd/MM/yyy")
        return format.format(date)
    }
}

使用扩展功能(文档)

@file:JvmName("DateUtils")//Use this to change your class name in java, by default is <the file name>Kt (DateUtilsKt in your case)

fun Date.toSimpleString() : String {
    val format = SimpleDateFormat("dd/MM/yyy")
    return format.format(this)
}

然后，您可以像已经做的那样直接在xml中使用它:

Then you can use it directly in xml as you are already doing:

android:text="@{DateUtils.toSimpleString(journey.date)}"

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