1. MyDialog.java

public class MyDialog extends Dialog {
    public MyDialog(@NonNull Context context) {
        super(context);
        setContentView(R.layout.dialog_layout);
    }
}

2. dialog_layout.xml

<?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"
    android:layout_width="300dp"
    android:layout_height="200dp">

    <TextView
        android:id="@+id/textView2"
        android:layout_width="218dp"
        android:layout_height="59dp"
        android:layout_marginTop="84dp"
        android:text="我是定製dialog"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.303"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:text="OK"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toStartOf="@+id/button3"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent" />

    <Button
        android:id="@+id/button3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:text="Cancel"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toEndOf="@+id/button2" />
</android.support.constraint.ConstraintLayout>
 

3. 呼叫

 MyDialog myDialog = new MyDialog(MainActivity.this);
            myDialog.show();

4. 效果圖：
   
5. demo原始碼：
   https://gitee.com/cxyzy1/custom_dialog/tree/master/simpleCustDialog

安卓開發技術分享: https://blog.csdn.net/yinxing2008/article/details/84555061