Activity的onCreate方法中，Kotlin视图变量意外地为null
我有一个小的Java Android Studio项目，我使用Android Studio 3.0 Canary 3中的Kotlin转换器将所有四个源文件转换为Kotlin。 然后我做了一些小的修改来编译。 我只有一个活动，下面的代码：
package com.ebelinski.soundboard import android.support.v7.app.AppCompatActivity import android.os.Bundle import android.widget.AdapterView import kotlinx.android.synthetic.main.activity_storyboard.gridview; class StoryboardActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val itemManager = ItemManager(applicationContext) val items = itemManager.getItems().toTypedArray<Item>() setContentView(R.layout.activity_storyboard) val storyboardAdapter = StoryboardAdapter(this, items) gridview.adapter = storyboardAdapter gridview.onItemClickListener = AdapterView.OnItemClickListener { parent, v, position, id -> // todo } } } 当我运行这个我得到以下错误：
06-05 10:25:42.758 5668-5668/? E/AndroidRuntime: FATAL EXCEPTION: main Process: com.ebelinski.soundboard, PID: 5668 java.lang.IllegalArgumentException: Parameter specified as non-null is null: method kotlin.jvm.internal.Intrinsics.checkParameterIsNotNull, parameter convertView at com.ebelinski.soundboard.StoryboardAdapter.getView(StoryboardAdapter.kt) at android.widget.AbsListView.obtainView(AbsListView.java:2363) at android.widget.GridView.onMeasure(GridView.java:1065) at android.view.View.measure(View.java:19857) at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715) at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461) at android.view.View.measure(View.java:19857) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083) at android.widget.FrameLayout.onMeasure(FrameLayout.java:185) at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139) at android.view.View.measure(View.java:19857) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083) at android.support.v7.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:393) at android.view.View.measure(View.java:19857) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083) at android.widget.FrameLayout.onMeasure(FrameLayout.java:185) at android.view.View.measure(View.java:19857) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083) at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464) at android.widget.LinearLayout.measureVertical(LinearLayout.java:758) at android.widget.LinearLayout.onMeasure(LinearLayout.java:640) at android.view.View.measure(View.java:19857) at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083) at android.widget.FrameLayout.onMeasure(FrameLayout.java:185) at com.android.internal.policy.DecorView.onMeasure(DecorView.java:689) at android.view.View.measure(View.java:19857) at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2275) at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1366) at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1619) at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1254) at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6337) at android.view.Choreographer$CallbackRecord.run(Choreographer.java:874) at android.view.Choreographer.doCallbacks(Choreographer.java:686) at android.view.Choreographer.doFrame(Choreographer.java:621) at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:860) at android.os.Handler.handleCallback(Handler.java:751) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6119) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
我不确定这里的问题是什么。 很明显， gridview为null，但我不知道为什么。 当我注释掉gridview.adapter和gridview.onItemClickListener ，至少程序不会崩溃。 在使用kotlin-android-extensions之前，我有同样的错误信息，并将问题变量定义为val gridView = findViewById(R.id.gridview) as GridView 。
相应的XML文件具有以下内容：
<?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:id="@+id/activity_storyboard" android:layout_width="match_parent" android:layout_height="match_parent" android:paddingBottom="@dimen/activity_vertical_margin" android:paddingLeft="@dimen/activity_horizontal_margin" android:paddingRight="@dimen/activity_horizontal_margin" android:paddingTop="@dimen/activity_vertical_margin" tools:context="com.ebelinski.soundboard.StoryboardActivity"> <GridView android:id="@+id/gridview" android:layout_width="match_parent" android:layout_height="match_parent" android:gravity="center" android:columnWidth="100dp" android:numColumns="auto_fit" android:verticalSpacing="24dp" android:horizontalSpacing="10dp" android:stretchMode="spacingWidthUniform" /> </RelativeLayout>
我原来的Java代码工作得很好，这个类是：
package com.ebelinski.soundboard; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.view.View; import android.widget.AdapterView; import android.widget.GridView; public class StoryboardActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); ItemManager itemManager = new ItemManager(getApplicationContext()); final Item[] items = itemManager.getItems().toArray(new Item[itemManager.getItems().size()]); setContentView(R.layout.activity_storyboard); GridView gridView = (GridView)findViewById(R.id.gridview); StoryboardAdapter storyboardAdapter = new StoryboardAdapter(this, items); gridView.setAdapter(storyboardAdapter); gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() { public void onItemClick(AdapterView<?> parent, View v, int position, long id) { // todo } }); } }
您需要在为其设置适配器之前初始化您的GridView 。
class StoryboardActivity : AppCompatActivity() { private lateinit var gridView: GridView override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val itemManager = ItemManager(applicationContext) val items = itemManager.getItems().toTypedArray<Item>() setContentView(R.layout.activity_storyboard) val storyboardAdapter = StoryboardAdapter(this, items) gridView = findViewById(R.id.gridview) as GridView gridview.adapter = storyboardAdapter gridview.onItemClickListener = AdapterView.OnItemClickListener { parent, v, position, id -> // todo } }
我认为问题是在kotlin-android-extensions，你的代码看起来不错，只是尝试清理项目，并改变网格视图的ID。 你也可以阅读有关配置kotlin-android-extensions的大文章，这是一个非常酷的工具，你会忘记findViewById。 也请尝试在稳定版本的工作室和android插件，并确保您将其导入主gradle文件，并在应用程序gradle文件中应用。