无法解析类android.support.constraint.ConstraintLayout

我这条线是红色的

<android.support.constraint.ConstraintLayout 

确保在

build.gradle（项目名称）

文件中声明了

maven.google.com

存储库：

将库作为依赖项添加到

build.gradle（模块：app）

文件：

要使用

约束布局

写入：

非常感谢您！但如何摆脱类似名称空间的东西，只需在布局xml中保留

ConstraintLayout

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/background"
    tools:context=".MainActivity">


    <Button
        android:id="@+id/act1Btn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginBottom="8dp"
        android:text="Bill Calculation"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/askOptions"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginBottom="8dp"
        android:text="What you want to do?"
        android:textColor="#00BCD4"
        android:textSize="30sp"
        app:layout_constraintBottom_toTopOf="@+id/act1Btn"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/btn3"
        android:layout_width="130dp"
        android:layout_height="55dp"
        android:layout_marginStart="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginBottom="8dp"
        android:text="Tax Calc"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/act1Btn" />

    <Button
        android:id="@+id/btn4"
        android:layout_width="142dp"
        android:layout_height="46dp"
        android:text="Mobile Tax"
        app:layout_constraintBottom_toTopOf="@+id/btn3"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/act1Btn" />
</android.support.constraint.ConstraintLayout>

repositories {
    google()
}

dependencies {
    implementation "androidx.constraintlayout:constraintlayout:2.0.4"
}