kotlin

问题 How to declare objects globally in kotlin like in java TextView tv; . Or any method to call the same variable in different methods/functions. override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) val textView: TextView = findViewById(R.id.texfirst) as TextView textView.setOnClickListener { Toast.makeText(applicationContext,"Welcome to Kotlin ! $abc "+textView.text, Toast.LENGTH_LONG).show() } myFunction(textView) } fun

问题 This is a general question. Let's say I have an extension function written in kotlin which converts DP to PX and return a NonNull Int fun Int.toPx() { /** implementation */ } The function in java will look something like this public int toPx(int $receiver) { /** implementation */ } In my opinion the $receiver makes the Java-interop feels generated and uninviting. I know that you can use the @JvmName annotation with some combinations like @file:JvmName to change the name in java. When i'm

问题 I've defined this class: class NeverNullMap<K, V>(private val backing: MutableMap<K, V> = mutableMapOf(), val default: () -> V): MutableMap<K, V> by backing { override operator fun get(key: K): V = backing.getOrPut(key, default) } And I can use it perfectly fine like this: fun main(args: Array<String>) { val myMap = NeverNullMap<String, Int> {0} println(myMap["test"]) myMap["test"] = myMap["test"] + 10 println(myMap["test"]) } as expected the output is: 0 10 But when I try to change it to:

问题 I've defined this class: class NeverNullMap<K, V>(private val backing: MutableMap<K, V> = mutableMapOf(), val default: () -> V): MutableMap<K, V> by backing { override operator fun get(key: K): V = backing.getOrPut(key, default) } And I can use it perfectly fine like this: fun main(args: Array<String>) { val myMap = NeverNullMap<String, Int> {0} println(myMap["test"]) myMap["test"] = myMap["test"] + 10 println(myMap["test"]) } as expected the output is: 0 10 But when I try to change it to:

问题 I've defined this class: class NeverNullMap<K, V>(private val backing: MutableMap<K, V> = mutableMapOf(), val default: () -> V): MutableMap<K, V> by backing { override operator fun get(key: K): V = backing.getOrPut(key, default) } And I can use it perfectly fine like this: fun main(args: Array<String>) { val myMap = NeverNullMap<String, Int> {0} println(myMap["test"]) myMap["test"] = myMap["test"] + 10 println(myMap["test"]) } as expected the output is: 0 10 But when I try to change it to:

问题 I've defined this class: class NeverNullMap<K, V>(private val backing: MutableMap<K, V> = mutableMapOf(), val default: () -> V): MutableMap<K, V> by backing { override operator fun get(key: K): V = backing.getOrPut(key, default) } And I can use it perfectly fine like this: fun main(args: Array<String>) { val myMap = NeverNullMap<String, Int> {0} println(myMap["test"]) myMap["test"] = myMap["test"] + 10 println(myMap["test"]) } as expected the output is: 0 10 But when I try to change it to:

问题 When IntelliJ IDEA detects I'm pasting a piece of copied Java code into a Kotlin file, it offers me to convert the pasted Java to Kotlin. This dialog contains a 'Do no ask again next time checkbox'. I checked this box and selected 'Yes', but now I want to undo my default choice. How do I do this? I've looked and searched in IntelliJ IDEA's preferences, but haven't found the respective checkbox. Is it actually in the settings, or can I somehow reset default checkbox selections? 回答1:

问题 After following this tutorial to create a screen for preferences, there seems to be a problem with inflating the class 'androidx.preference.PreferenceScreen'. Why is it not found when my preferences have been declared inside the res/xml folder and the necessary dependency has been added to this project? My app's minSdkVersion is 24. Error inflating class (not found)androidx.preference.PreferenceScreen dependencies dependencies { implementation fileTree(dir: 'libs', include: ['*.jar'])

问题 After following this tutorial to create a screen for preferences, there seems to be a problem with inflating the class 'androidx.preference.PreferenceScreen'. Why is it not found when my preferences have been declared inside the res/xml folder and the necessary dependency has been added to this project? My app's minSdkVersion is 24. Error inflating class (not found)androidx.preference.PreferenceScreen dependencies dependencies { implementation fileTree(dir: 'libs', include: ['*.jar'])

问题 After following this tutorial to create a screen for preferences, there seems to be a problem with inflating the class 'androidx.preference.PreferenceScreen'. Why is it not found when my preferences have been declared inside the res/xml folder and the necessary dependency has been added to this project? My app's minSdkVersion is 24. Error inflating class (not found)androidx.preference.PreferenceScreen dependencies dependencies { implementation fileTree(dir: 'libs', include: ['*.jar'])