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Kotlin中 四个提升逼格的关键字你都会了吗?

let

let扩展函数的实际上是一个效果域函数,当你需求去定义一个变量在一个特定的效果域范围内,let函数的是一个不错的选择;let函数另一个效果便是能够避免写一些判断null的操作。

  • let函数的一般结构
object.let{
it.todo()//在函数体内运用it替代object目标去拜访其公有的特点和办法
...
}
//另一种用途 判断object为null的操作
object?.let{//表明object不为null的条件下,才会去履行let函数体
it.todo()
}
  • let函数的kotlin和Java转化
//kotlin
 fun main(args: Array<String>) {
    val result = "testLet".let {
        println(it.length)
        1000
    }
    println(result)
 }
 //java
 public final class LetFunctionKt {
   public static final void main(@NotNull String[] args) {
      Intrinsics.checkParameterIsNotNull(args, "args");
      String var2 = "testLet";
      int var4 = var2.length();
      System.out.println(var4);
      int result = 1000;
      System.out.println(result);
   }
}
  • let函数运用前后的比照
mVideoPlayer?.setVideoView(activity.course_video_view)
    mVideoPlayer?.setControllerView(activity.course_video_controller_view)
    mVideoPlayer?.setCurtainView(activity.course_video_curtain_view)
------------------------------------------------------------------------------------------------------------------------------
mVideoPlayer?.let {
       it.setVideoView(activity.course_video_view)
       it.setControllerView(activity.course_video_controller_view)
       it.setCurtainView(activity.course_video_curtain_view)
}
  • let函数适用的场景

场景一: 最常用的场景便是运用let函数处理需求针对一个可null的目标统一做判空处理。 场景二: 然后便是需求去明确一个变量所在特定的效果域范围内能够运用

with

  • with函数运用的一般结构
with(object){
   //todo
 }
  • with函数的kotlin和Java转化
//kotlin
fun main(args: Array<String>) {
    val user = User("Kotlin", 1, "1111111")
    val result = with(user) {
        println("my name is $name, I am $age years old, my phone number is $phoneNum")
        1000
    }
    println("result: $result")
}
------------------------------------------------------------------------------------------------------------------------------
//java
 public static final void main(@NotNull String[] args) {
      Intrinsics.checkParameterIsNotNull(args, "args");
      User user = new User("Kotlin", 1, "1111111");
      String var4 = "my name is " + user.getName() + ", I am " + user.getAge() + " years old, my phone number is " + user.getPhoneNum();
      System.out.println(var4);
      int result = 1000;
      String var3 = "result: " + result;
      System.out.println(var3);
   }
  • with函数运用前后的比照
override fun onBindViewHolder(holder: ViewHolder, position: Int){
   val item = getItem(position)?: return
   with(item){
      holder.tvNewsTitle.text = StringUtils.trimToEmpty(titleEn)
       holder.tvNewsSummary.text = StringUtils.trimToEmpty(summary)
       holder.tvExtraInf.text = "难度:$gradeInfo | 单词数:$length | 读后感: $numReviews"
   }
}
------------------------------------------------------------------------------------------------------------------------------
@Override
public void onBindViewHolder(ViewHolder holder, int position) {
   ArticleSnippet item = getItem(position);
        if (item == null) {
            return;
        }
        holder.tvNewsTitle.setText(StringUtils.trimToEmpty(item.titleEn));
        holder.tvNewsSummary.setText(StringUtils.trimToEmpty(item.summary));
        String gradeInfo = "难度:" + item.gradeInfo;
        String wordCount = "单词数:" + item.length;
        String reviewNum = "读后感:" + item.numReviews;
        String extraInfo = gradeInfo + " | " + wordCount + " | " + reviewNum;
        holder.tvExtraInfo.setText(extraInfo);
}
  • with函数的适用的场景 适用于调用同一个类的多个办法时,能够省去类名重复,直接调用类的办法即可,常常用于Android中RecyclerView中onBinderViewHolder中,数据model的特点映射到UI上

run

  • run函数运用的一般结构
object.run{
//todo
}
  • run函数的kotlin和Java转化
//java
  public static final void main(@NotNull String[] args) {
      Intrinsics.checkParameterIsNotNull(args, "args");
      User user = new User("Kotlin", 1, "1111111");
      String var5 = "my name is " + user.getName() + ", I am " + user.getAge() + " years old, my phone number is " + user.getPhoneNum();
      System.out.println(var5);
      int result = 1000;
      String var3 = "result: " + result;
      System.out.println(var3);
   }
------------------------------------------------------------------------------------------------------------------------------
//kotlin
fun main(args: Array<String>) {
    val user = User("Kotlin", 1, "1111111")
    val result = user.run {
        println("my name is $name, I am $age years old, my phone number is $phoneNum")
        1000
    }
    println("result: $result")
}
  • run函数运用前后比照
override fun onBindViewHolder(holder: ViewHolder, position: Int){
   val item = getItem(position)?: return
   with(item){
      holder.tvNewsTitle.text = StringUtils.trimToEmpty(titleEn)
       holder.tvNewsSummary.text = StringUtils.trimToEmpty(summary)
       holder.tvExtraInf = "难度:$gradeInfo | 单词数:$length | 读后感: $numReviews"
       ...   
   }
}
// 运用后
override fun onBindViewHolder(holder: ViewHolder, position: Int){
  getItem(position)?.run{
      holder.tvNewsTitle.text = StringUtils.trimToEmpty(titleEn)
       holder.tvNewsSummary.text = StringUtils.trimToEmpty(summary)
       holder.tvExtraInf = "难度:$gradeInfo | 单词数:$length | 读后感: $numReviews"
       ...   
   }
}
  • run函数运用场景

适用于let,with函数任何场景。由于run函数是let,with两个函数结合体,准确来说它弥补了let函数在函数体内有必要运用it参数替代目标,在run函数中能够像with函数相同能够省掉,直接拜访实例的公有特点和办法,另一方面它弥补了with函数传入目标判空问题,在run函数中能够像let函数相同做判空处理

apply

  • apply函数运用的一般结构
object.apply{
//todo
}
  • apply函数的kotlin和Java转化
//java
public final class ApplyFunctionKt {
   public static final void main(@NotNull String[] args) {
      Intrinsics.checkParameterIsNotNull(args, "args");
      User user = new User("Kotlin", 1, "1111111");
      String var5 = "my name is " + user.getName() + ", I am " + user.getAge() + " years old, my phone number is " + user.getPhoneNum();
      System.out.println(var5);
      String var3 = "result: " + user;
      System.out.println(var3);
   }
}
//kotlin
fun main(args: Array<String>) {
    val user = User("Kotlin", 1, "1111111")
    val result = user.apply {
        println("my name is $name, I am $age years old, my phone number is $phoneNum")
        1000
    }
    println("result: $result")
}
  • apply函数运用前后的比照
//运用前
mSheetDialogView = View.inflate(activity, R.layout.biz_exam_plan_layout_sheet_inner, null)
        mSheetDialogView.course_comment_tv_label.paint.isFakeBoldText = true
        mSheetDialogView.course_comment_tv_score.paint.isFakeBoldText = true
        mSheetDialogView.course_comment_tv_cancel.paint.isFakeBoldText = true
        mSheetDialogView.course_comment_tv_confirm.paint.isFakeBoldText = true
        mSheetDialogView.course_comment_seek_bar.max = 10
        mSheetDialogView.course_comment_seek_bar.progress = 0
//运用后
mSheetDialogView = View.inflate(activity, R.layout.biz_exam_plan_layout_sheet_inner, null).apply{
   course_comment_tv_label.paint.isFakeBoldText = true
   course_comment_tv_score.paint.isFakeBoldText = true
   course_comment_tv_cancel.paint.isFakeBoldText = true
   course_comment_tv_confirm.paint.isFakeBoldText = true
   course_comment_seek_bar.max = 10
   course_comment_seek_bar.progress = 0
}
//多级判空
    if (mSectionMetaData == null || mSectionMetaData.questionnaire == null || mSectionMetaData.section == null) {
            return;
        }
        if (mSectionMetaData.questionnaire.userProject != null) {
            renderAnalysis();
            return;
        }
        if (mSectionMetaData.section != null && !mSectionMetaData.section.sectionArticles.isEmpty()) {
            fetchQuestionData();
            return;
        }
    mSectionMetaData?.apply{
    //mSectionMetaData不为空的时分操作mSectionMetaData
    }?.questionnaire?.apply{
    //questionnaire不为空的时分操作questionnaire
    }?.section?.apply{
    //section不为空的时分操作section
    }?.sectionArticle?.apply{
    //sectionArticle不为空的时分操作sectionArticle
    }

also

  • also函数运用的一般结构
object.also{
//todo
}

仿制

  • also函数编译后的class文件
//java
public final class AlsoFunctionKt {
   public static final void main(@NotNull String[] args) {
      Intrinsics.checkParameterIsNotNull(args, "args");
      String var2 = "testLet";
      int var4 = var2.length();
      System.out.println(var4);
      System.out.println(var2);
   }
}
//kotlin
fun main(args: Array<String>) {
    val result = "testLet".also {
        println(it.length)
        1000
    }
    println(result)
}
  • also函数的适用场景

适用于let函数的任何场景,also函数和let很像,仅仅唯一的不同点便是let函数最终的回来值是最终一行的回来值而also函数的回来值是回来当前的这个目标。一般可用于多个扩展函数链式调用

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