android开发分享学习《第一行代码》第三版敲的代码

由于主要在acitivity_main.xml和MainActivity.kt, 这里一般只展示这两个
然后代码用到的资源(例如图片)请自行到 第一行代码——Android(第3版)图灵社区下载

4.1 至 4.2

acitivity_main.xml

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="https://schemas.android.com/apk/res/android"     xmlns:app="https://schemas.android.com/apk/res-auto"     xmlns:tools="https://schemas.android.com/tools"     android:layout_width="match_parent"     android:layout_height="match_parent"     android:orientation="vertical"     tools:context=".MainActivity">      <TextView         android:id="@+id/textView"         android:layout_width="match_parent"         android:layout_height="wrap_content"         android:text="This is TextView"         android:gravity="center"         android:textColor="#00ff00"         android:textSize="24sp"         tools:ignore="HardcodedText" />          <Button             android:id="@+id/button"             android:layout_width="match_parent"             android:layout_height="wrap_content"             android:text="Button"             android:textSize="30sp"             android:textAllCaps="false"             tools:ignore="HardcodedText"             />          <EditText             android:id="@+id/editText"             android:layout_width="match_parent"             android:layout_height="wrap_content"             android:hint="Type something here"             android:maxLines="2"             tools:ignore="HardcodedText" />          <ImageView             android:id="@+id/imageView"             android:layout_width="wrap_content"             android:layout_height="wrap_content"             android:src="@drawable/grape_pic"/>          <ProgressBar             android:id="@+id/progressBar"             android:layout_width="match_parent"             android:layout_height="wrap_content"             style="?android:attr/progressBarStyleHorizontal"             android:max="100"/> </LinearLayout> 

MainActivity.kt

package com.example.helloworld  import androidx.appcompat.app.AppCompatActivity import android.os.Bundle import android.util.Log import android.view.View import android.widget.Toast import androidx.appcompat.app.AlertDialog import kotlinx.android.synthetic.main.activity_main.*   class MainActivity : AppCompatActivity(), View.OnClickListener {     private var flag = 0      override fun onCreate(savedInstanceState: Bundle?) {         super.onCreate(savedInstanceState)         setContentView(R.layout.activity_main)         button.setOnClickListener(this)     }      override fun onClick(v: View?) {         when (v?.id) {             R.id.button -> { //                val inputText = editText.text.toString() //                Toast.makeText(this, inputText, Toast.LENGTH_SHORT).show()                  when (flag) {                     0 -> imageView.setImageResource(R.drawable.cherry_pic)                     1 -> imageView.setImageResource(R.drawable.grape_pic)                     2 -> imageView.setImageResource(R.drawable.watermelon_pic)                     3 -> imageView.setImageResource(R.drawable.strawberry_pic)                 }                 flag = (flag + 1) % 4  //                AlertDialog.Builder(this).apply { //                    setTitle("你点开了Dialog") //                    setMessage("Something important") //                    setCancelable(false) //                    setPositiveButton("Ok") {dialog, which -> //                    } //                    setNegativeButton("Cancel"){dialog, which-> //                    } //                    show() //                }                  progressBar.progress = (progressBar.progress + 25) % 110             }          }     } } 

4.4自定义组件

MainActivity.kt

package com.example.helloworld  import androidx.appcompat.app.AppCompatActivity import android.os.Bundle   class MainActivity : AppCompatActivity(){     override fun onCreate(savedInstanceState: Bundle?){         super.onCreate(savedInstanceState)         setContentView(R.layout.activity_main)         supportActionBar?.hide()     } } 

activity_main.xml

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="https://schemas.android.com/apk/res/android"     xmlns:app="https://schemas.android.com/apk/res-auto"     xmlns:tools="https://schemas.android.com/tools"     android:layout_width="match_parent"     android:layout_height="match_parent"     tools:context=".MainActivity">      <com.example.helloworld.TitleLayout         android:layout_width="match_parent"         android:layout_height="wrap_content"/> </LinearLayout> 

TitleLayout.kt

package com.example.helloworld  import android.app.Activity import android.content.Context import android.util.AttributeSet import android.view.LayoutInflater import android.widget.LinearLayout import android.widget.Toast import kotlinx.android.synthetic.main.title.view.*   class TitleLayout(context: Context, attrs: AttributeSet): LinearLayout(context, attrs){     init {         LayoutInflater.from(context).inflate(R.layout.title, this)         titleBack.setOnClickListener{             val activity = context as Activity             activity.finish()         }         titleEdit.setOnClickListener{             Toast.makeText(context, "you clicked Edit button", Toast.LENGTH_SHORT).show()         }     } } 

4.5ListView

MainActivity.kt

package com.example.helloworld  import androidx.appcompat.app.AppCompatActivity import android.os.Bundle import android.widget.ArrayAdapter import kotlinx.android.synthetic.main.activity_main.*   class MainActivity : AppCompatActivity(){     private val data = listOf("Apple", "Banana", "Orange", "Watermelon",         "Pear", "Grape", "Pineapple", "strawberry", "Cherry", "Mango",         "Pear", "Grape", "Pineapple", "strawberry", "Cherry")      override fun onCreate(savedInstanceState: Bundle?){         super.onCreate(savedInstanceState)         setContentView(R.layout.activity_main)         val adapter = ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, data)         listView.adapter = adapter     } } 

activity_main.xml

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="https://schemas.android.com/apk/res/android"     xmlns:app="https://schemas.android.com/apk/res-auto"     xmlns:tools="https://schemas.android.com/tools"     android:layout_width="match_parent"     android:layout_height="match_parent"     tools:context=".MainActivity">      <ListView         android:id="@+id/listView"         android:layout_height="match_parent"         android:layout_width="match_parent"/>  </LinearLayout> 

主要由下列四个文件构成
MainActivity.kt

package com.example.helloworld  import androidx.appcompat.app.AppCompatActivity import android.os.Bundle import android.widget.Toast import kotlinx.android.synthetic.main.activity_main.*   class MainActivity : AppCompatActivity(){     private val fruitList = ArrayList<Fruit>()      override fun onCreate(savedInstanceState: Bundle?){         super.onCreate(savedInstanceState)         setContentView(R.layout.activity_main)         initFruits()         val adapter = FruitAdapter(this, R.layout.fruit_item, fruitList)         listView.adapter = adapter         listView.setOnItemClickListener{_, _, position, _->             val fruit = fruitList[position]             Toast.makeText(this, fruit.name, Toast.LENGTH_SHORT).show()         }     }      private fun initFruits(){         repeat(2){             fruitList.add(Fruit("Apple", R.drawable.apple_pic))             fruitList.add(Fruit("Banana", R.drawable.banana_pic))             fruitList.add(Fruit("Orange", R.drawable.orange_pic))             fruitList.add(Fruit("Watermelon", R.drawable.watermelon_pic))             fruitList.add(Fruit("Pear", R.drawable.pear_pic))             fruitList.add(Fruit("Grape", R.drawable.grape_pic))             fruitList.add(Fruit("Pineapple", R.drawable.pineapple_pic))             fruitList.add(Fruit("Strawberry", R.drawable.strawberry_pic))             fruitList.add(Fruit("Cherry", R.drawable.cherry_pic))             fruitList.add(Fruit("Mango", R.drawable.mango_pic))         }     } } 

activity_main.xml

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="https://schemas.android.com/apk/res/android"     xmlns:app="https://schemas.android.com/apk/res-auto"     xmlns:tools="https://schemas.android.com/tools"     android:layout_width="match_parent"     android:layout_height="match_parent"     tools:context=".MainActivity">      <ListView         android:id="@+id/listView"         android:layout_height="match_parent"         android:layout_width="match_parent"/>  </LinearLayout> 

fruit_item.xml

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="https://schemas.android.com/apk/res/android"     xmlns:tools="https://schemas.android.com/tools"     android:layout_width="match_parent"     android:layout_height="60dp">      <ImageView         android:id="@+id/fruitImage"         android:layout_width="40dp"         android:layout_height="40dp"         android:layout_gravity="center_vertical"         android:layout_marginLeft="10dp"         tools:ignore="ContentDescription,RtlHardcoded" />      <TextView         android:id="@+id/fruitName"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:layout_gravity="center_vertical"         android:layout_marginLeft="10dp"         tools:ignore="RtlHardcoded" />  </LinearLayout> 

FruitAdapter.kt

package com.example.helloworld  import android.app.Activity import android.view.View import android.view.ViewGroup import android.widget.ArrayAdapter import android.widget.ImageView import android.widget.TextView import android.view.LayoutInflater  class FruitAdapter(activity: Activity, val resourceId: Int, data: List<Fruit>): ArrayAdapter<Fruit>(activity, resourceId, data){     inner class ViewHolder(val fruitImage: ImageView, val fruitName: TextView)      override fun getView(position: Int, convertView: View?, parent: ViewGroup): View {         val view: View         val viewHolder: ViewHolder         if (convertView == null) {             view = LayoutInflater.from(context).inflate(resourceId, parent, false)             val fruitImage: ImageView = view.findViewById(R.id.fruitImage)             val fruitName: TextView = view.findViewById(R.id.fruitName)             viewHolder = ViewHolder(fruitImage, fruitName)             view.tag = viewHolder         } else {             view = convertView             viewHolder = view.tag as ViewHolder         }         var fruit = getItem(position)         if(fruit != null){             viewHolder.fruitImage.setImageResource(fruit.imageId)             viewHolder.fruitName.text = fruit.name         }         return view     } }