Kotlin学习（十九）: 属性自动生成方法所引发问题

在Kotlin中创建一个属性，如果是val，那么会自动生成getter方法，如果是var，那么会自动生成getter和setter方法。

class MethodFoo() {    var a: Int = 1    var b: Int = 2}

生成的class内容

public final class MethodFoo {   private int a = 1;   private int b = 2;   public final int getA() {      return this.a;   }   public final void setA(int var1) {      this.a = var1;   }   public final int getB() {      return this.b;   }   public final void setB(int var1) {      this.b = var1;   }}

自动生成get和set

在开发的时候，经常会用到一些常量，而常量一般放在一个公共的类里面，在Kotlin中，我们是这样写的：

object Constant {    val ACTION_FINDVIEWBYID = "FindViewById"    val ACTION_BUTTERKNIFE = "ButterKnife"    val SELECTED_TEXT_SUFFIX = ".xml"    val PSI_METHOD_BY_ONCREATE = "onCreate"    val PSI_METHOD_BY_ONCREATEVIEW = "onCreateView"    val CREATOR_COMMAND_NAME = "Generate Injections"    val CLASS_TYPE_BY_ACTIVITY = "activity"    val CLASS_TYPE_BY_FRAGMENT = "fragment"    val FIELD_ON_CLICK = "OnClick"    val FIELD_ONCLICK = "onClick"}

生成的代码是这样的：

public final class Constant {   @NotNull   private static final String ACTION_FINDVIEWBYID = "FindViewById";   @NotNull   private static final String ACTION_BUTTERKNIFE = "ButterKnife";   @NotNull   private static final String SELECTED_TEXT_SUFFIX = ".xml";   @NotNull   private static final String PSI_METHOD_BY_ONCREATE = "onCreate";   @NotNull   private static final String PSI_METHOD_BY_ONCREATEVIEW = "onCreateView";   @NotNull   private static final String CREATOR_COMMAND_NAME = "Generate Injections";   @NotNull   private static final String CLASS_TYPE_BY_ACTIVITY = "activity";   @NotNull   private static final String CLASS_TYPE_BY_FRAGMENT = "fragment";   @NotNull   private static final String FIELD_ON_CLICK = "OnClick";   @NotNull   private static final String FIELD_ONCLICK = "onClick";   public static final Constant INSTANCE;   @NotNull   public final String getACTION_FINDVIEWBYID() {      return ACTION_FINDVIEWBYID;   }   @NotNull   public final String getACTION_BUTTERKNIFE() {      return ACTION_BUTTERKNIFE;   }   @NotNull   public final String getSELECTED_TEXT_SUFFIX() {      return SELECTED_TEXT_SUFFIX;   }   @NotNull   public final String getPSI_METHOD_BY_ONCREATE() {      return PSI_METHOD_BY_ONCREATE;   }   @NotNull   public final String getPSI_METHOD_BY_ONCREATEVIEW() {      return PSI_METHOD_BY_ONCREATEVIEW;   }   @NotNull   public final String getCREATOR_COMMAND_NAME() {      return CREATOR_COMMAND_NAME;   }   @NotNull   public final String getCLASS_TYPE_BY_ACTIVITY() {      return CLASS_TYPE_BY_ACTIVITY;   }   @NotNull   public final String getCLASS_TYPE_BY_FRAGMENT() {      return CLASS_TYPE_BY_FRAGMENT;   }   @NotNull   public final String getFIELD_ON_CLICK() {      return FIELD_ON_CLICK;   }   @NotNull   public final String getFIELD_ONCLICK() {      return FIELD_ONCLICK;   }   private Constant() {      INSTANCE = (Constant)this;      ACTION_FINDVIEWBYID = "FindViewById";      ACTION_BUTTERKNIFE = "ButterKnife";      SELECTED_TEXT_SUFFIX = ".xml";      PSI_METHOD_BY_ONCREATE = "onCreate";      PSI_METHOD_BY_ONCREATEVIEW = "onCreateView";      CREATOR_COMMAND_NAME = "Generate Injections";      CLASS_TYPE_BY_ACTIVITY = "activity";      CLASS_TYPE_BY_FRAGMENT = "fragment";      FIELD_ON_CLICK = "OnClick";      FIELD_ONCLICK = "onClick";   }   static {      new Constant();   }}

这….生成了那么多的get方法，如果我有100个字段，那么就多生成了100个get方法，我只是想要Constant.fieldName这样子调用这个字段而已，根本不需要用到get，这样明显是创建了多余的方法，方法数增多容易报65535错。

如何避免生成

在Kotlin中，可以使用两种方法来停止自动生成get和set方法。

使用const关键字

object Constant {    const val ACTION_FINDVIEWBYID = "FindViewById"    const val ACTION_BUTTERKNIFE = "ButterKnife"    const val SELECTED_TEXT_SUFFIX = ".xml"    const val PSI_METHOD_BY_ONCREATE = "onCreate"    const val PSI_METHOD_BY_ONCREATEVIEW = "onCreateView"    const val CREATOR_COMMAND_NAME = "Generate Injections"    const val CLASS_TYPE_BY_ACTIVITY = "activity"    const val CLASS_TYPE_BY_FRAGMENT = "fragment"    const val FIELD_ON_CLICK = "OnClick"    const val FIELD_ONCLICK = "onClick"}

来看一下编译后的内容

public final class Constant {   @NotNull   public static final String ACTION_FINDVIEWBYID = "FindViewById";   @NotNull   public static final String ACTION_BUTTERKNIFE = "ButterKnife";   @NotNull   public static final String SELECTED_TEXT_SUFFIX = ".xml";   @NotNull   public static final String PSI_METHOD_BY_ONCREATE = "onCreate";   @NotNull   public static final String PSI_METHOD_BY_ONCREATEVIEW = "onCreateView";   @NotNull   public static final String CREATOR_COMMAND_NAME = "Generate Injections";   @NotNull   public static final String CLASS_TYPE_BY_ACTIVITY = "activity";   @NotNull   public static final String CLASS_TYPE_BY_FRAGMENT = "fragment";   @NotNull   public static final String FIELD_ON_CLICK = "OnClick";   @NotNull   public static final String FIELD_ONCLICK = "onClick";   public static final Constant INSTANCE;   private Constant() {      INSTANCE = (Constant)this;   }   static {      new Constant();   }}

使用@JvmField注解

object Constant {    @JvmField val ACTION_FINDVIEWBYID = "FindViewById"    @JvmField val ACTION_BUTTERKNIFE = "ButterKnife"    @JvmField val SELECTED_TEXT_SUFFIX = ".xml"    @JvmField val PSI_METHOD_BY_ONCREATE = "onCreate"    @JvmField val PSI_METHOD_BY_ONCREATEVIEW = "onCreateView"    @JvmField val CREATOR_COMMAND_NAME = "Generate Injections"    @JvmField val CLASS_TYPE_BY_ACTIVITY = "activity"    @JvmField val CLASS_TYPE_BY_FRAGMENT = "fragment"    @JvmField val FIELD_ON_CLICK = "OnClick"    @JvmField val FIELD_ONCLICK = "onClick"}

来看一下编译后的内容

public final class Constant {   @JvmField   @NotNull   public static final String ACTION_FINDVIEWBYID = "FindViewById";   @JvmField   @NotNull   public static final String ACTION_BUTTERKNIFE = "ButterKnife";   @JvmField   @NotNull   public static final String SELECTED_TEXT_SUFFIX = ".xml";   @JvmField   @NotNull   public static final String PSI_METHOD_BY_ONCREATE = "onCreate";   @JvmField   @NotNull   public static final String PSI_METHOD_BY_ONCREATEVIEW = "onCreateView";   @JvmField   @NotNull   public static final String CREATOR_COMMAND_NAME = "Generate Injections";   @JvmField   @NotNull   public static final String CLASS_TYPE_BY_ACTIVITY = "activity";   @JvmField   @NotNull   public static final String CLASS_TYPE_BY_FRAGMENT = "fragment";   @JvmField   @NotNull   public static final String FIELD_ON_CLICK = "OnClick";   @JvmField   @NotNull   public static final String FIELD_ONCLICK = "onClick";   public static final Constant INSTANCE;   private Constant() {      INSTANCE = (Constant)this;      ACTION_FINDVIEWBYID = "FindViewById";      ACTION_BUTTERKNIFE = "ButterKnife";      SELECTED_TEXT_SUFFIX = ".xml";      PSI_METHOD_BY_ONCREATE = "onCreate";      PSI_METHOD_BY_ONCREATEVIEW = "onCreateView";      CREATOR_COMMAND_NAME = "Generate Injections";      CLASS_TYPE_BY_ACTIVITY = "activity";      CLASS_TYPE_BY_FRAGMENT = "fragment";      FIELD_ON_CLICK = "OnClick";      FIELD_ONCLICK = "onClick";   }   static {      new Constant();   }}

后记

当我们使用Kotlin定义大量的公共字段的时候，一定要这样写来避免方法数过多。

感谢Kotlin属性引发的方法数问题。