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解决kotlin 安卓 'no name provided' is impossible, because 'recycler_view.adapter' is a complex expre

解决Kotlin错误:Smart cast is impossible, because the property could have been changed by this time

xll1990 2017.12.13 阅读 6156

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使用Kotlin开发Android应用,在向列表添加Nullable值时Android Studio提示:

Smart cast to 'String' is impossible, because 'a.name' is a mutable property that could have been changed by this time

示例如下

class A {

var name: String? = null

}

class B {

val names: ArrayList<String> = ArrayList()

public fun addNames(a: A) {

if(a.name != null) {

names.add(a.name);

}

}

}

查了一下,报这个错误的原因是:在别的线程可以对Nullable值a.name做修改,这样在执行names.add(a.name)时它的值有可能为null。

解决

为了避免添加null值,有几种做法:

1、使用val声明nullable值,这样nullable值就不可能被修改

class A {

val name: String? = null

}

2、把nullable值赋值给一个新的变量,然后再做其他操作

public fun addNames(a: A) {

val name = a.name

if(name != null) {

names.add(name);

}

}

3、使用?let语法糖

a.name?.let { name -> names.add(name) }

a.name?.let { names.add(it) }

a.name?.let(names::add)

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