1. “null cannot be cast to non-null type”错误的含义 “null cannot be cast to non-null type”这个错误发生在尝试将一个null值强制转换为非空类型时。在Kotlin中,所有变量默认都是非空的,除非明确声明为可空类型(使用?后缀)。如果在运行时尝试将一个null值赋给一个非空类型的变量,就会发生这个错误。
null as Map<String, String>? 如果要将这个变量赋值给一个Map<String, String>,编译时依然不会出错,但在运行时,则将出现一个非常难以debug的问题: java.lang.NullPointerException: null cannot be cast to non-null type kotlin.collections.MutableMap<kotlin.String, kotlin.String> 如图所示:编辑...
TotalPrice有值,会导致GrossAmount也为null --即NULL+任何数字都会是NULL --NULL不能和任何字段比较和...
TotalPrice有值,会导致GrossAmount也为null --即NULL+任何数字都会是NULL --NULL不能和任何字段比较和...
?意味着如果findViewByIdreturn null,那么 thisnull将被分配给val toolbar而不是上升kotlin.TypeCastException: null cannot be cast to non-null type android.support.v7.widget.Toolbar异常 完整代码块示例: val toolbar = findViewById(R.id.toolbar) as Toolbar? // toolbar now is nullable if(toolbar...
1. String str = null; // null can be assigned to String 2. Integer itr = null; // you can assign null to Integer also 3. Double dbl = null; // null can also be assigned to Double 4. 5. String myStr = (String) null; // null can be type cast to String ...
[7.20.3-1] If the space cannot be allocated, a null pointer is returned. 对于空指针值,一般的文档(比如 man)中倾向于用 NULL 表示,而没有直接说成 0。但是我们应该清楚:对于指针类型来说,返回 NULL 和 返回 0 是完全等价的,因为 NULL 和 0 都表示 “null pointer”(空指针)。(tyc:一般系统中手册...
publicstringName {get=> name;set=> name =value??thrownewArgumentNullException(nameof(value),"Name cannot be null"); } The preceding example also demonstrates how to useexpression-bodied membersto define a property. You can use the??=operator to replace the code of the form ...
Applications should throw instances of this class to indicate other illegal uses of the null object. NullPointerException objects may be constructed by the virtual machine as if Throwable#Throwable(String, Throwable, boolean, boolean) suppression were disabled and/or the stack trace was not writable...
collections.MutableListEN使CartAdapter接受可空参数dataList，因为您的api请求可能返回null并传递它将导致...