错误：包android.databinding不存在

Question

我正在构建我的第一个 Android 应用程序。我正在按照 Android Authority 的本教程制作计算器应用程序：https://www.androidauthority.com/build-a-calculator-app-721910

我安装了最新版本的 Android Studio，Gradle 也是最新的。几天以来我一直在寻找这个问题的解决方案。我参考了许多 StackOverflow 答案，也研究了我自己的代码。使用 Sync Project 与 Gradle 文件时，我没有收到任何错误。仅当我构建 APK 时才会弹出该错误。这是我收到的错误：

error: package android.databinding does not exist
error: package android.support.v7.app does not exist
error: package com.sample.foo.samplecalculator.databinding does not exist
error: cannot find symbol AppCompactActivity
cannot find symbol ActivityMainBinding

这是我的 MainActivity.java 文件：

package com.example.calculator;

import android.databinding.DataBindingUtil;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;

import com.sample.foo.samplecalculator.databinding.ActivityMainBinding;

import java.text.DecimalFormat;

public class MainActivity extends AppCompactActivity {

    private ActivityMainBinding binding;

    private static final char ADDITION = '+';
    private static final char SUBTRACTION = '-';
    private static final char MULTIPLICATION = '*';
    private static final char DIVISION = '/';

    private char CURRENT_ACTION;

    private double valueOne = Double.NaN;
    private double valueTwo;

    private DecimalFormat decimalFormat;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        decimalFormat = new DecimalFormat("#.##########");

        binding = DataBindingUtil.setContentView(this, R.layout.activity_main);

        binding.buttonDot.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                binding.editText.setText(binding.editText.getText() + ".");
            }
        });

        binding.buttonZero.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                binding.editText.setText(binding.editText.getText() + "0");
            }
        });

        binding.buttonOne.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                binding.editText.setText(binding.editText.getText() + "1");
            }
        });

        binding.buttonTwo.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                binding.editText.setText(binding.editText.getText() + "2");
            }
        });

        binding.buttonThree.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                binding.editText.setText(binding.editText.getText() + "3");
            }
        });

        binding.buttonFour.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                binding.editText.setText(binding.editText.getText() + "4");
            }
        });

        binding.buttonFive.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                binding.editText.setText(binding.editText.getText() + "5");
            }
        });

        binding.buttonSix.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                binding.editText.setText(binding.editText.getText() + "6");
            }
        });

        binding.buttonSeven.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                binding.editText.setText(binding.editText.getText() + "7");
            }
        });

        binding.buttonEight.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                binding.editText.setText(binding.editText.getText() + "8");
            }
        });

        binding.buttonNine.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                binding.editText.setText(binding.editText.getText() + "9");
            }
        });

        binding.buttonAdd.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                computeCalculation();
                CURRENT_ACTION = ADDITION;
                binding.infoTextView.setText(decimalFormat.format(valueOne) + "+");
                binding.editText.setText(null);
            }
        });

        binding.buttonSubtract.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                computeCalculation();
                CURRENT_ACTION = SUBTRACTION;
                binding.infoTextView.setText(decimalFormat.format(valueOne) + "-");
                binding.editText.setText(null);
            }
        });

        binding.buttonMultiply.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                computeCalculation();
                CURRENT_ACTION = MULTIPLICATION;
                binding.infoTextView.setText(decimalFormat.format(valueOne) + "*");
                binding.editText.setText(null);
            }
        });

        binding.buttonDivide.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                computeCalculation();
                CURRENT_ACTION = DIVISION;
                binding.infoTextView.setText(decimalFormat.format(valueOne) + "/");
                binding.editText.setText(null);
            }
        });

        binding.buttonEqual.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                computeCalculation();
                binding.infoTextView.setText(binding.infoTextView.getText().toString() +
                        decimalFormat.format(valueTwo) + " = " + decimalFormat.format(valueOne));
                valueOne = Double.NaN;
                CURRENT_ACTION = '0';
            }
        });

        binding.buttonClear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if(binding.editText.getText().length() > 0) {
                    CharSequence currentText = binding.editText.getText();
                    binding.editText.setText(currentText.subSequence(0, currentText.length()-1));
                }
                else {
                    valueOne = Double.NaN;
                    valueTwo = Double.NaN;
                    binding.editText.setText("");
                    binding.infoTextView.setText("");
                }
            }
        });
    }

    private void computeCalculation() {
        if(!Double.isNaN(valueOne)) {
            valueTwo = Double.parseDouble(binding.editText.getText().toString());
            binding.editText.setText(null);

            if(CURRENT_ACTION == ADDITION)
                valueOne = this.valueOne + valueTwo;
            else if(CURRENT_ACTION == SUBTRACTION)
                valueOne = this.valueOne - valueTwo;
            else if(CURRENT_ACTION == MULTIPLICATION)
                valueOne = this.valueOne * valueTwo;
            else if(CURRENT_ACTION == DIVISION)
                valueOne = this.valueOne / valueTwo;
        }
        else {
            try {
                valueOne = Double.parseDouble(binding.editText.getText().toString());
            }
            catch (Exception e){}
        }
    }
}

这是我的activity_main.xml 文件的代码：

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

    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/activity_main"
        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=".MainActivity">

        <TextView
            android:id="@+id/infoTextView"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginBottom="30dp"
            android:textSize="30sp" />

        <EditText
            android:id="@+id/editText"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_below="@id/infoTextView"
            android:enabled="false"
            android:gravity="bottom"
            android:lines="2"
            android:maxLines="2"
            android:textSize="20sp" />

        <Button
            android:id="@+id/buttonSeven"
            style="@style/Widget.AppCompat.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@id/editText"
            android:text="7"
            android:textSize="20sp" />

        <Button
            android:id="@+id/buttonEight"
            style="@style/Widget.AppCompat.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@id/editText"
            android:layout_toRightOf="@id/buttonSeven"
            android:text="8"
            android:textSize="20sp" />

        <Button
            android:id="@+id/buttonNine"
            style="@style/Widget.AppCompat.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@id/editText"
            android:layout_toRightOf="@id/buttonEight"
            android:text="9"
            android:textSize="20sp" />

        <Button
            android:id="@+id/buttonFour"
            style="@style/Widget.AppCompat.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@id/buttonSeven"
            android:text="4"
            android:textSize="20sp" />

        <Button
            android:id="@+id/buttonFive"
            style="@style/Widget.AppCompat.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignRight="@id/buttonEight"
            android:layout_below="@id/buttonEight"
            android:text="5"
            android:textSize="20sp" />

        <Button
            android:id="@+id/buttonSix"
            style="@style/Widget.AppCompat.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignRight="@id/buttonNine"
            android:layout_below="@id/buttonNine"
            android:text="6"
            android:textSize="20sp" />

        <Button
            android:id="@+id/buttonOne"
            style="@style/Widget.AppCompat.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@id/buttonFour"
            android:text="1"
            android:textSize="20sp" />

        <Button
            android:id="@+id/buttonTwo"
            style="@style/Widget.AppCompat.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignRight="@id/buttonEight"
            android:layout_below="@id/buttonFive"
            android:text="2"
            android:textSize="20sp" />

        <Button
            android:id="@+id/buttonThree"
            style="@style/Widget.AppCompat.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignRight="@id/buttonNine"
            android:layout_below="@id/buttonSix"
            android:text="3"
            android:textSize="20sp" />

        <Button
            android:id="@+id/buttonDot"
            style="@style/Widget.AppCompat.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@id/buttonOne"
            android:text="."
            android:textSize="20sp" />

        <Button
            android:id="@+id/buttonZero"
            style="@style/Widget.AppCompat.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignRight="@id/buttonEight"
            android:layout_below="@id/buttonTwo"
            android:text="0"
            android:textSize="20sp" />

        <Button
            android:id="@+id/buttonEqual"
            style="@style/Widget.AppCompat.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignRight="@id/buttonNine"
            android:layout_below="@id/buttonThree"
            android:text="="
            android:textSize="20sp" />

        <Button
            android:id="@+id/buttonDivide"
            style="@style/Widget.AppCompat.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignTop="@id/buttonNine"
            android:layout_toRightOf="@id/buttonNine"
            android:text="/"
            android:textSize="20sp" />

        <Button
            android:id="@+id/buttonMultiply"
            style="@style/Widget.AppCompat.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignTop="@id/buttonSix"
            android:layout_toRightOf="@id/buttonSix"
            android:text="*"
            android:textSize="20sp" />

        <Button
            android:id="@+id/buttonSubtract"
            style="@style/Widget.AppCompat.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignTop="@id/buttonThree"
            android:layout_toRightOf="@id/buttonThree"
            android:text="-"
            android:textSize="20sp" />

        <Button
            android:id="@+id/buttonAdd"
            style="@style/Widget.AppCompat.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignTop="@id/buttonEqual"
            android:layout_toRightOf="@id/buttonEqual"
            android:text="+"
            android:textSize="20sp" />

        <Button
            android:id="@+id/buttonClear"
            style="@style/Widget.AppCompat.Button.Borderless"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignRight="@id/buttonAdd"
            android:layout_below="@id/buttonAdd"
            android:layout_marginTop="@dimen/activity_vertical_margin"
            android:text="C"
            android:textSize="20sp" />
    </RelativeLayout>
</layout>

build.gradle(app)如下：

    apply plugin: 'com.android.application'

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.3"
    dataBinding.enabled = true

    defaultConfig {
        applicationId "com.example.calculator"
        minSdkVersion 16
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }

}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])

    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
}

Answer 1

我也遇到了同样的问题。在 buildTypes 下面添加这个解决了我的问题：

buildFeatures {
    viewBinding true
}