使用 Kotlin 按字母对数组进行排序

如果您想要排序到列表的副本中，惯用的方法是对List使用sortedBy扩展方法.或者，如果您想在没有副本的情况下就地排序，请在MutableList上使用sortBy分机.ArrayList可以作为任一列表类型工作.

// Sort a readonly list into a copy of the list

val appsList: List<AppInfo> = ...

val sortedAppsList = appsList.sortedBy { it.label?.toString() }

对比:

// Sort a mutable list in-place

val appsList: MutableList<AppInfo> = ...

appList.sortBy { it.label?.toString() }

and if holding as an ArrayList it is the same, but not idiomatic to have a reference directly to this concrete type.

// Sort an ArrayList list into a copy of the list

val appsList: ArrayList<AppInfo> = ...  // ALERT! not idiomatic

val sortedAppsList = appsList.sortedBy { it.label?.toString() }

// or if you want, feel free to sort in-place

appsList.sortBy { it.label?.toString() }

Note the toString() on the label: CharSequence member. You have to be careful sorting on a reference of type CharSequence as it is undefined what is its behavior for sorting (see: https://docs.oracle.com/javase/7/docs/api/java/lang/CharSequence.html)

This interface does not refine the general contracts of the equals and hashCode methods. The result of comparing two objects that implement CharSequence is therefore, in general, undefined.

如果CharSequence已经是String(很可能是)，那么呼叫toString()没有什么坏处，因为它只是返回自己.

还请记住，还必须处理可为null的CharSequence，并且您需要决定在哪里使用null:在列表的开头或结尾.我认为默认的做法是让他们从头开始.

Other notes about your code in the question:

Use the List or MutableList interface instead of the concrete class to reference the type, and use the methods from Kotlin stdlib to do actions upon the list. Also use val instead of var for references that will not change (meaning it will always point to the same list regardless of whether the list contents could change).

你的if大声明可以减少很多，从...

if(app.label?.toString()!!.length >= searchWord.length && app.label?.toString()!!.substring(0, searchWord.length) == searchWord.toUpperCase() && searchWord != "" ||
    app.label?.toString()!!.length >= searchWord.length && app.label?.toString()!!.substring(0, searchWord.length) == searchWord.toLowerCase() && searchWord != "" ||
    app.label?.toString()!!.length >= searchWord.length && app.label?.toString()!!.substring(0, searchWord.length) == searchWord.capitalize() && searchWord != "" ||
    app.label?.toString()!!.length >= searchWord.length && app.label?.toString()!!.substring(0, searchWord.length) == searchWord && searchWord != ""){

    if(app.packageName != "com.david.launcher" ){
        Appslist.add(app)
    }

}
if(searchWord == ""){
    if(app.packageName != "com.david.launcher"){
        Appslist.add(app)
    }
}

to simpler:

if (app.packageName != "com.david.launcher" &&
        (searchWord.isBlank() || 
         app.label?.startsWith(searchWord, ignoreCase = true) == true)) {
    appsList.add(app)
}

You should browse the standard library to get an idea of what is available so that you broaden your toolkit for the future.