這是我使用 android Kotlin 從實時資料庫中讀取異步資料的代碼：
class suDetails : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_su_details)
su_image.setOnClickListener {
readData(object : MyCallback {
override fun onCallback(imageUrl: String?) {
if (imageUrl != null) {
val imageViewer = Intent(baseContext, suDetails::class.java)
imageViewer.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK)
imageViewer.putExtra("su_image", imageUrl)
startActivity(imageViewer)
}
}
})
}
}
fun readData(myCallback: MyCallback) {
val su_resource =intent
val su_res = su_resource.getStringExtra("su_userid")
val suRef = FirebaseDatabase.getInstance().getReference().child("Users").child(su_res!!)
suRef.addValueEventListener(object : ValueEventListener {
override fun onDataChange(dataSnapshot: DataSnapshot) {
if(dataSnapshot.exists()){
su_layout.visibility = View.VISIBLE
val userData = dataSnapshot.getValue(profile_model::class.java)
val imageUrl = userData!!.getImageUrl()
Picasso.get().load(imageUrl).placeholder(R.drawable.ic_baseline_image_200).into(su_image)
su_name.text = userData.getnameOfsu()
Toast.makeText(baseContext, imageUrl, Toast.LENGTH_LONG).show()
myCallback.onCallback(imageUrl)
}
}
override fun onCancelled(error: DatabaseError) {
}
})
}
interface MyCallback {
fun onCallback(value: String?)
}
}
我已經提到其他問題以從實時資料庫中讀取異步資料，但是當我嘗試該解決方案時，我無法在我的ImageView和textView. 我只得到空白螢屏。
Tyler V 回答后的新代碼：
class suDetails : AppCompatActivity() {
private var currentImageUrl: String = ""
private var su_res: String = ""
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_su_details)
su_res = intent.getStringExtra("su_userid").toString()
// get views
val su_name = findViewById<TextView>(R.id.su_name)
val su_image = findViewById<ImageView>(R.id.su_image)
// onClick launches another activity - if the image
// hasn't loaded yet nothing happens
su_image.setOnClickListener { viewCurrentImage() }
// start the async loading right away - once it is loaded the
// su_layout view will be visible and the view data
// will be populated. It might be good to show a progress bar
// while it's loading
readData()
}
fun readData() {
println("LOG: called readData")
Toast.makeText(baseContext, su_res, Toast.LENGTH_LONG).show()
println("LOG: getting data for ${su_res}")
val suRef = FirebaseDatabase.getInstance()
.getReference()
.child("Users")
.child(su_res)
suRef.addValueEventListener(object : ValueEventListener {
override fun onDataChange(dataSnapshot: DataSnapshot) {
if (dataSnapshot.exists()) {
println("LOG: data snapshot exists")
su_layout.visibility = View.VISIBLE
val userData = dataSnapshot.getValue(profile_model::class.java)
currentImageUrl = userData?.getImageUrl() ?: ""
su_name.text = userData?.getnameOfsu() ?: ""
println("LOG: Got user data ${currentImageUrl}")
if (currentImageUrl.isNotEmpty()) {
Picasso.get()
.load(currentImageUrl)
.placeholder(R.drawable.ic_baseline_image_200)
.into(su_image)
}
} else {
println("LOG: user not found in database")
}
}
override fun onCancelled(error: DatabaseError) {
println("LOG: cancelled")
}
})
}
private fun viewCurrentImage() {
if (currentImageUrl.isEmpty()) return
Toast.makeText(baseContext, currentImageUrl, Toast.LENGTH_LONG).show()
val imageViewer = Intent(baseContext, ImageViewer::class.java)
imageViewer.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK)
imageViewer.putExtra("su_image", currentImageUrl)
startActivity(imageViewer)
}
}
uj5u.com熱心網友回復：
此相關問題的最佳答案向您展示了如何進行回呼，但這并不能真正回答如何使用異步資料的問題，并且與此類問題沒有真正的幫助或相關性。
我看不出你的回呼有什么特別的錯誤——但它默默地吞下了許多可能的錯誤情況（例如，如果用戶不存在）。下面的示例有一些列印陳述句，應該有助于更好地確定正在發生的事情。
比額外的回呼介面更簡潔的方法是創建一個單獨的方法來處理異步結果。這是一個清理后的示例，說明了它的外觀 - 帶有一些偽代碼，其中部分示例丟失了。為了幫助除錯，如果您不了解代碼的哪些部分正在運行，或者某些東西看起來不像您期望的那樣，您應該養成使用 log 或 print 陳述句的習慣。
private var currentImageUrl: String = ""
private var userId: String = ""
private lateinit var su_name: TextView
private lateinit var su_image : ImageView
private lateinit var su_layout : ConstraintLayout
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_su_details)
// get views
su_name = findViewById<TextView>(R.id.su_name)
su_image = findViewById<ImageView>(R.id.su_image)
su_layout = findViewById<ConstraintLayout>(R.id.su_layout)
su_layout.visibility = View.INVISIBLE
// get user id from intent
userId = intent.getStringExtra("su_userid").orEmpty()
// TODO: Handle what to do if userId is empty here!
if( userId.isEmpty() ) {
finish()
}
// onClick launches another activity - if the image
// hasn't loaded yet nothing happens
su_image.setOnClickListener { viewCurrentImage() }
// start the async loading right away - once it is loaded the
// su_layout view will be visible and the view data
// will be populated. It might be good to show a progress bar
// while it's loading
startLoading()
}
private fun startLoading() {
println("LOG: getting data for ${userId}")
val suRef = FirebaseDatabase.getInstance()
.getReference()
.child("Users")
.child(userId)
suRef.addValueEventListener(object : ValueEventListener {
override fun onDataChange(dataSnapshot: DataSnapshot) {
if(dataSnapshot.exists()) {
println("LOG: data snapshot exists")
val userData = dataSnapshot.getValue(profile_model::class.java)
showData(userData)
}
else {
println("LOG: user not found in database")
}
}
override fun onCancelled(error: DatabaseError) {
println("LOG: cancelled")
}
})
}
private fun showData(userData: profile_model?) {
su_layout.visibility = View.VISIBLE
currentImageUrl = userData?.getImageUrl() ?: ""
su_name.text = userData?.getnameOfsu() ?: "Error"
println("LOG: Got user data ${currentImageUrl}")
if( currentImageUrl.isNotEmpty() ) {
Picasso.get()
.load(currentImageUrl)
.placeholder(R.drawable.ic_baseline_image_200)
.into(su_image)
}
}
private fun viewCurrentImage() {
if( currentImageUrl.isEmpty() ) return
val imageViewer = Intent(this, suDetails::class.java)
imageViewer.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK)
imageViewer.putExtra("su_image", currentImageUrl)
startActivity(imageViewer)
}
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標籤：安卓 科特林 异步 firebase-实时数据库