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。

Kotlin学习（十九）: 属性自动生成方法所引发问题

自动生成get和set

如何避免生成

使用const关键字

使用@JvmField注解

后记

自动生成`get`和`set`

使用`const`关键字

使用`@JvmField`注解