android - java.lang.IllegalStateException : DataBindingUtil. inflate(...) 在尝试使用 DataBindingUtil 膨胀时不能为 null

Question

我有一个 BaseFragment 类:

abstract class BaseFragment: Fragment(), View.OnClickListener {

    private lateinit var mBinding: ViewDataBinding

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        mBinding = DataBindingUtil.inflate<ViewDataBinding>(inflater, getLayoutId() , container, false)

        return mBinding.root
    }

    abstract fun getLayoutId(): Int

    abstract fun afterOnViewCreated()


    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        afterOnViewCreated()
    }

    override fun onSaveInstanceState(outState: Bundle) {
        super.onSaveInstanceState(outState)
    }

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

    override fun onClick(v: View?) { }

    fun getViewDataBinding(): ViewDataBinding {
        return mBinding
    }

    fun setClickListener(vararg views: View) {
        views.forEach { view -> view.setOnClickListener(this) }
    }

}

我扩展它来创建这样的新 fragment :

class HomeFragment : BaseFragment() {

    private lateinit var homeViewModel: HomeViewModel

    override fun getLayoutId(): Int {
        return R.layout.fragment_home
    }

    override fun afterOnViewCreated() {
        activity?.let{
            homeViewModel = ViewModelProviders.of(this).get(HomeViewModel::class.java)
        }
        //TODO:
    }

}

但是，我遇到了这个崩溃:

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.mu.chatonymous, PID: 23328
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example/com.example.MainActivity}: java.lang.IllegalStateException: DataBindingUtil.inflate<…nt_home, container, false) must not be null
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3318)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3429)
        at android.app.ActivityThread.-wrap12(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2009)
        at android.os.Handler.dispatchMessage(Handler.java:109)
        at android.os.Looper.loop(Looper.java:166)
        at android.app.ActivityThread.main(ActivityThread.java:7555)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:469)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:963)
     Caused by: java.lang.IllegalStateException: DataBindingUtil.inflate<…nt_home, container, false) must not be null
        at com.mu.chatonymous.ui.base.BaseFragment.onCreateView(BaseFragment.kt:21)
        at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2612)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:874)
        at androidx.fragment.app.FragmentManagerImpl.addAddedFragments(FragmentManagerImpl.java:2087)
        at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1861)
        at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1817)
        at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManagerImpl.java:1717)
        at androidx.fragment.app.FragmentManagerImpl.dispatchStateChange(FragmentManagerImpl.java:2650)
        at androidx.fragment.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManagerImpl.java:2600)
        at androidx.fragment.app.Fragment.performActivityCreated(Fragment.java:2639)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:897)
        at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1228)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1293)
        at androidx.fragment.app.FragmentManagerImpl.dispatchStateChange(FragmentManagerImpl.java:2646)
        at androidx.fragment.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManagerImpl.java:2600)
        at androidx.fragment.app.FragmentController.dispatchActivityCreated(FragmentController.java:246)
        at androidx.fragment.app.FragmentActivity.onStart(FragmentActivity.java:542)
        at androidx.appcompat.app.AppCompatActivity.onStart(AppCompatActivity.java:176)
        at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1340)
        at android.app.Activity.performStart(Activity.java:7364)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3281)

这是我的应用级 build.gradle 文件:

apply plugin: 'com.android.application'

apply plugin: 'kotlin-android'

apply plugin: 'kotlin-android-extensions'

apply plugin: 'kotlin-kapt'

apply plugin: "androidx.navigation.safeargs.kotlin"

apply plugin: 'io.fabric'


android {
    compileSdkVersion 29
    buildToolsVersion "29.0.2"
    defaultConfig {
        applicationId "com.mu.chatonymous"
        minSdkVersion 19
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"

        multiDexEnabled true
        vectorDrawables.useSupportLibrary = true

    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    dataBinding {
        enabled = true
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }

    lintOptions {
        checkReleaseBuilds false
        // Or, if you prefer, you can continue to check for errors in release builds,
        // but continue the build even when errors are found:
        abortOnError false
    }
}


//androidx
dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation"org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'androidx.core:core-ktx:1.1.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'

    implementation 'androidx.lifecycle:lifecycle-runtime:2.1.0'
    implementation 'androidx.lifecycle:lifecycle-extensions:2.1.0'
    kapt 'androidx.lifecycle:lifecycle-compiler:2.1.0'
    implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.1.0'

    implementation 'androidx.multidex:multidex:2.0.1'

    implementation 'androidx.navigation:navigation-fragment-ktx:2.1.0'
    implementation 'androidx.navigation:navigation-ui-ktx:2.1.0'

    implementation 'androidx.recyclerview:recyclerview:1.1.0'
    //for selection single or multiple items in recycler view
    implementation 'androidx.recyclerview:recyclerview-selection:1.0.0'


}
//test
dependencies {
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
}
//google
dependencies {
    implementation 'com.google.android.material:material:1.0.0'
    implementation 'com.google.code.gson:gson:2.8.5'

    implementation 'com.google.firebase:firebase-core:17.2.1'
    implementation 'com.google.firebase:firebase-analytics:17.2.1'
    implementation 'com.crashlytics.sdk.android:crashlytics:2.10.1'
    implementation 'com.google.firebase:firebase-auth:19.2.0'
}
//3rd party
dependencies {
    implementation 'com.jakewharton.timber:timber:4.7.1'
}

apply plugin: 'com.google.gms.google-services'

我做错了什么？我知道我可以使用 LayoutInflater.inflate 而不是 DatabindingUtil.inflate，但我以前使用这个流程没有问题。我有点像我在这里做的那样需要 viewDataBinding 对象供以后使用。

Answer 1

好的，所以我发现了问题。事实证明，即使您正确配置了几乎所有设置，您也可能会忘记/错过这个小信息。所以，我将在这里分享我学到的东西。

数据绑定(bind)布局文件略有不同，以 <layout> 的根标记开始后跟数据元素和 View 根元素。 如此处详细所述:Official Databinding Documentation

所以用 <layout></layout> 包裹你所有的布局将补救此异常。

例如:

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android">
   <androidx.constraintlayout.widget.ConstraintLayout
       android:layout_width="match_parent"
       android:layout_height="match_parent">

       ....

   </androidx.constraintlayout.widget.ConstraintLayout>
</layout>