如何将值从ViewList反映到ViewModel类？

编程问答 2022-06-12

问题描述

我目前正在使用带有Kotlin的android-studio开发应用程序。

此应用具有

就我的代码而言，即使我选择了ListView数组中的初始值，活动也不会显示我选择的值...

如何解决此问题？

以下是代码：

build.gradle 

apply plugin: 'com.android.application'

apply plugin: 'kotlin-android'

apply plugin: 'kotlin-android-extensions'

android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "com.sample.arrayvaluetest"
        minSdkVersion 16
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'),'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation filetree(dir: 'libs',include: ['*.jar'])
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
    implementation 'androidx.appcompat:appcompat:1.0.0-beta01'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    implementation 'androidx.legacy:legacy-support-v4:1.0.0-beta01'
    implementation 'androidx.recyclerview:recyclerview:1.0.0-beta01'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test:runner:1.1.0-alpha4'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.0-alpha4'

    implementation "com.google.android.material:material:1.1.0-alpha06"

    def nav_version = '2.0.0'
    implementation "androidx.navigation:navigation-fragment-ktx:$nav_version"
    implementation "androidx.navigation:navigation-ui-ktx:$nav_version"

    implementation "androidx.fragment:fragment-ktx:1.3.0-alpha04"

}

AppState.kt 

package com.sample.arrayvaluetest

import androidx.lifecycle.viewmodel


class AppState: viewmodel() {

    var array = arrayOf("one","two","three")
    var arrayIndex:Int = 0
}

MainActivity，kt 

package com.sample.arrayvaluetest

import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button
import android.widget.TextView
import androidx.lifecycle.viewmodelProvider

class MainActivity : AppCompatActivity() {

    lateinit var appState: AppState

    override fun onCreate(savedInstanceState: Bundle?) {

        appState = viewmodelProvider(this).get(AppState::class.java)

        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val text = findViewById<TextView>(R.id.text)
        val button = findViewById<Button>(R.id.button)

        text.text = appState.array[appState.arrayIndex]

        button.setonClickListener {
            val intent = Intent(this,ListActivity::class.java)
            startActivity(intent)
        }

    }
}

activity_main.xml 

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

    <TextView
            android:id="@+id/text"
            android:text="initial text"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent"/>

    <Button
            android:id="@+id/button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="to list"
            android:layout_marginTop="32dp"
            app:layout_constraintTop_toBottomOf="@+id/text"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
    />

</androidx.constraintlayout.widget.ConstraintLayout>

ListActivity.kt 

package com.sample.arrayvaluetest

import android.os.Bundle
import android.widget.ArrayAdapter
import android.widget.ListView
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
import androidx.lifecycle.viewmodelProvider

class ListActivity : AppCompatActivity() {

    lateinit var appState: AppState

    override fun onCreate(savedInstanceState: Bundle?) {

        appState = viewmodelProvider(this).get(AppState::class.java)

        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_list)

        val listView = findViewById<ListView>(R.id.listView)

        val adapter = ArrayAdapter(this,android.R.layout.simple_list_item_1,appState.array)

        listView.adapter = adapter

        listView.setonItemClickListener { parent,view,position,id ->
            val item = (view.findViewById<TextView>(android.R.id.text1)).text

            when (item) {
                "one" -> appState.arrayIndex = 0
                "two" -> appState.arrayIndex = 1
                "three" -> appState.arrayIndex = 2
            }
            println(appState.arrayIndex)

            finish()
        }
    }
}

activity_list.xml 

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".ListActivity">

    <ListView
            android:id="@+id/listView"
            android:layout_width="match_parent"
            android:layout_height="match_parent"/>
    
</androidx.constraintlayout.widget.ConstraintLayout>

Android Studio：3.3.2

解决方法

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androidandroidandroid-listviewandroid-viewmodel