Kotlin的意图

Question

所以,我知道在Java中我们使用它来推出新的 Activity

Intent intent = new Intent(this, SomeActivity.class);
startActivity(intent);

但是我正在用Kotlin写一个项目,所以在Kotlin中它就像

val intent = Intent(this,SomeActivity::class.java)
startActivity(intent)

但它崩溃了问题

FATAL EXCEPTION: main
Process: com.pashabred.passlin, PID: 15243
                                                                           java.lang.RuntimeException: Unable to start activity ComponentInfo{com.pashabred.passlin/com.pashabred.passlin.Enterring}: kotlin.KotlinNullPointerException
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
    at android.app.ActivityThread.access$800(ActivityThread.java:151)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:135)
    at android.app.ActivityThread.main(ActivityThread.java:5254)
    at java.lang.reflect.Method.invoke(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:372)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
                                                                            Caused by: kotlin.KotlinNullPointerException
    at com.pashabred.passlin.Enterring.onCreate(Enterring.kt:17)
    at android.app.Activity.performCreate(Activity.java:5990)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
    at android.app.ActivityThread.access$800(ActivityThread.java:151) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:135) 
    at android.app.ActivityThread.main(ActivityThread.java:5254) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:372) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 

Answer 1

使用Kotlin for Android的意图几乎相同,我们只需要在语法中稍微改变如下.

val intent = Intent(this,HelloActivity::class.java) startActivity(intent)

您获得的异常onCreate是活动方法中的空指针异常,请检查相同的..

Answer 2

确保你有(问号):

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
}

代替:

override fun onCreate(savedInstanceState: Bundle) {
    super.onCreate(savedInstanceState)
}

Answer 3

我用来打开新活动的最短也是最简单的方法

startActivity(Intent(this@MainActivity, NextActivity::class.java))

PS:这里需要注意的一点是Intent()期望将packageContext作为第一个参数,因此只使用它仍会引发错误.

因此,您需要明确定义类名.如上面一行所示(这个@ MainActivity)