Question

我正在Android活动中从Firestore数据库中读取数据，并将数据存储在ArrayList中，但是当我打印出ArrayList时，我得到的是最后一个条目，而没有其他条目

这是我的Kotlin代码：

   override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_counties)

        var sites : ArrayList<Site> = ArrayList<Site>()
        var site : Site = Site()

        val selectedCounty: String = intent.getStringExtra("COUNTY")

        sites.clear()

        db.collection("UKSites")
            .document("England")
            .collection("Counties")
            .document(selectedCounty)
            .collection(selectedCounty)
            .get()
            .addOnSuccessListener { documents ->
                for (document in documents) {

                    site.name = document.data["Name"].toString()
                    site.address?.line1 = document.data["Address Line 1"].toString()
                    site.address?.line2 = document.data["Address Line 2"].toString()
                    site.address?.line3 = document.data["Address Line 3"].toString()
                    site.address?.line4 = document.data["Address Line 4"].toString()
                    site.address?.postcode = document.data["Postcode"].toString()
                    site.address?.phoneNumber = document.data["Telephone"].toString()
                    site.address?.siteURL = document.data["Site URL"].toString()
                    site.description = document.data["Description"].toString()
                    site.price = document.data["Price"] as Double
                    site.distance = 0
                    site.locationCoordinate?.Longitude = document.data["Longitude"] as Double
                    site.locationCoordinate?.Latitude = document.data["Latitude"] as Double

                    sites.add(site)

                    Log.i("Info","${sites.last().name}")

                }

                Log.i("Info", "${sites.size}")

                for ( nextSite in sites ) {
                    Log.i("Info", "site.name = ${nextSite.name}")
                }

                // Recycler View code here
            }
            .addOnFailureListener { exception ->
                Log.w("Error", "Error getting documents: ", exception)
            }

这是输出到Logcat窗口的输出：

    2020-01-18 15:22:14.376 10629-10658/com.riverstonetech.gositeuk D/FA:   Logging event (FE): screen_view(_vs), Bundle[{ga_event_origin(_o)=auto,   ga_previous_class(_pc)=CountriesActivity,  ga_previous_id(_pi)=-7126357891560843792,  ga_screen_class(_sc)=CountiesActivity, ga_screen_id(_si)=-7126357891560843791}]
    2020-01-18 15:22:14.396 10629-10629/com.riverstonetech.gositeuk  I/Info: Stroud Farm
    2020-01-18 15:22:14.399 10629-10629/com.riverstonetech.gositeuk I/Info: Bennets Wood Farm
    2020-01-18 15:22:14.401 10629-10629/com.riverstonetech.gositeuk I/Info: Bluebell Farm
    2020-01-18 15:22:14.404 10629-10629/com.riverstonetech.gositeuk I/Info: Pinecopse Kennels
    2020-01-18 15:22:14.407 10629-10629/com.riverstonetech.gositeuk I/Info: Pinecopse Kennels
    2020-01-18 15:22:14.410 10629-10629/com.riverstonetech.gositeuk I/Info: Bennets Wood Farm
    2020-01-18 15:22:14.414 10629-10629/com.riverstonetech.gositeuk I/Info: Bluebell Farm
    2020-01-18 15:22:14.416 10629-10629/com.riverstonetech.gositeuk I/Info: Stroud Farm
    2020-01-18 15:13:20.486 10221-10221/com.riverstonetech.gositeuk I/Info: 8
    2020-01-18 15:13:20.486 10221-10221/com.riverstonetech.gositeuk I/Info: site.name = Stroud Farm
    2020-01-18 15:13:20.486 10221-10221/com.riverstonetech.gositeuk I/Info: site.name = Stroud Farm
    2020-01-18 15:13:20.486 10221-10221/com.riverstonetech.gositeuk I/Info: site.name = Stroud Farm
    2020-01-18 15:13:20.486 10221-10221/com.riverstonetech.gositeuk I/Info: site.name = Stroud Farm
    2020-01-18 15:13:20.486 10221-10221/com.riverstonetech.gositeuk I/Info: site.name = Stroud Farm
    2020-01-18 15:13:20.486 10221-10221/com.riverstonetech.gositeuk I/Info: site.name = Stroud Farm
    2020-01-18 15:13:20.486 10221-10221/com.riverstonetech.gositeuk I/Info: site.name = Stroud Farm
    2020-01-18 15:13:20.487 10221-10221/com.riverstonetech.gositeuk I/Info: site.name = Stroud Farm
    2020-01-18 15:13:20.502 10221-10252/com.riverstonetech.gositeuk D/EGL_emulation:     eglMakeCurrent: 0xae085060: ver 3 0 (tinfo 0xae083400)
    2020-01-18 15:13:20.524 10221-10252/com.riverstonetech.gositeuk D/EGL_emulation: eglMakeCurrent: 0xae085060: ver 3 0 (tinfo 0xae083400)
    2020-01-18 15:13:20.578 10221-10252/com.riverstonetech.gositeuk D/EGL_emulation: eglMakeCurrent: 0xae085060: ver 3 0 (tinfo 0xae083400)

Answer 1

您仅创建一次Site对象。因此，在循环中使用时，您只是一次又一次地重置相同对象的值。这就是从循环中获取最后一个元素的值的原因。

您每次都需要创建对象。因此var site : Site = Site()必须在for-each循环内。如下

for (document in documents) {
   // Create object here
   var site : Site = Site()
   // Then do your tasks what is currently doing
   site.name = document.data["Name"].toString()
   ....

}

为什么我不能在Kotlin中读取ArrayList的内容

1 个答案: