Kotlin + 数据绑定在输入'??' 处没有可行的替代方案

Question

Please excuse my poor English.

I'm using AndroidStudio3.1.1, I've tried to use data binding my project with kotlin , but I get an error when I'm trying to run the project. The error message that I'm getting is like below:

e: [kapt] An exception occurred: android.databinding.tool.util.LoggedErrorException: Found data binding errors. ****/ data binding error ****msg:Syntax error: no viable alternative at input '??' file:/Users/eraise/Code/Demo/app/src/main/res/layout/layout_main.xml loc:20:28 - 20:64 ****\\ data binding error ****

I can compile apk on Terminal due command: ./gradlew assembleDebug, that works fine.

My top-level build.gradle has this configuration:

buildscript {
ext.kotlin_version = '1.2.31'
repositories {
    google()
    jcenter()
}
dependencies {
    classpath 'com.android.tools.build:gradle:3.1.1'
    classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

allprojects {
    repositories {
        google()
        jcenter()
        maven { url 'https://www.jitpack.io'}
    }
}

My build.gradle in app dir (only relevant parts):

apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'
apply plugin: 'kotlin-kapt'
android{
    compileSdkVersion 27
    buildToolsVersion 27.1.0
    dataBinding {
        enabled = true
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}
dependencies {
    kapt "com.android.databinding:compiler:3.1.1"
}

My layout_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<layout>

    <data>
        <variable
            name="version"
            type="String"/>
    </data>

    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
                  xmlns:app="http://schemas.android.com/apk/res-auto"
                  android:layout_width="match_parent"
                  android:layout_height="match_parent"
                  android:orientation="vertical">

        <TextView
            android:id="@+id/tv_version_name"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:padding="10dp"
            android:text='@{"测试" + version??"unknow", default=版本号}'
            />

        <android.support.v7.widget.RecyclerView
            android:id="@+id/rv"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="#EEE"                    
            app:layoutManager="android.support.v7.widget.LinearLayoutManager"
            />

    </LinearLayout>
</layout>

Error on the line: android:text='@{"测试" + version??"unknow", default=版本号}'

LayoutMainBinding snippet:

@Override
protected void executeBindings() {
    long dirtyFlags = 0;
    synchronized(this) {
        dirtyFlags = mDirtyFlags;
        mDirtyFlags = 0;
    }
    java.lang.String version = mVersion;
    java.lang.String javaLangStringVersion = null;
    java.lang.String javaLangStringVersionJavaLangObjectNullJavaLangStringUnknowJavaLangStringVersion = null;
    boolean javaLangStringVersionJavaLangObjectNull = false;

    if ((dirtyFlags & 0x3L) != 0) {


            // Here's ?????? is 测试 if correct result.
            // read ("??????") + (version)
            javaLangStringVersion = ("??????") + (version);


            // read ("??????") + (version) == null
            javaLangStringVersionJavaLangObjectNull = (javaLangStringVersion) == (null);
        if((dirtyFlags & 0x3L) != 0) {
            if(javaLangStringVersionJavaLangObjectNull) {
                    dirtyFlags |= 0x8L;
            }
            else {
                    dirtyFlags |= 0x4L;
            }
        }
    }
    // batch finished

    if ((dirtyFlags & 0x3L) != 0) {

            // read ("??????") + (version) == null ? "unknow" : ("??????") + (version)
            javaLangStringVersionJavaLangObjectNullJavaLangStringUnknowJavaLangStringVersion = ((javaLangStringVersionJavaLangObjectNull) ? ("unknow") : (javaLangStringVersion));
    }
    // batch finished
    if ((dirtyFlags & 0x3L) != 0) {
        // api target 1

        android.databinding.adapters.TextViewBindingAdapter.setText(this.tvVersionName, javaLangStringVersionJavaLangObjectNullJavaLangStringUnknowJavaLangStringVersion);
    }
}

I can run correct if do not use kotlin

Answer 1

I think the problem is with the braces. Try to do it this way:

@{"test" + (user.name??"unknow", default=versionnumber)}'

Answer 2

I think you set the wrong expression for

android:text='@{"测试" + version??"unknow", default=版本号}'

I mean, what are you trying to achieve with this? Is it if version is null then return "unknown", and if it's not, return 版本号? I think also because you didn't use "" (double quotes) in your 版本号

If you want to express it that way, try this one:

android:text='@{"测试" + (version != null ? "版本号" : "unknown")}'

Expected Result

If version != null -> 测试版本号

If version == null -> 测试unknown

I tried and it works! But if the expected result is not what you want, let me know and we can work around it.

Answer 3

This problem cause by kapt not works well with Chinese character. So replace them with English or set your computer env as below：

JAVA_TOOL_OPTIONS=-Dfile.encoding=UTF8