CustomView

@SuppressLint("AppCompatCustomView")
public class CustomView extends TextView {
    Paint paint;
    int i=0;
    public CustomView(Context context) {
        super(context);
        init();
    }

    public CustomView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

    }

    private void changeText(){
        setText(String.valueOf(getNums()));
        if(i%2==0){
            setBackgroundColor(Color.BLACK);
        }else{
            setBackgroundColor(Color.RED);
        }
        i++;
    }

    private int getNums() {
        //獲取隨機數Math.random()，取值範圍[0, 1);
        //所有*9000後取值範圍 [0, 9000)
        //最後加上1000，範圍[1000, 10000)
        return (int) (Math.random()*9000+1000);
    }

    private void init() {
        changeText();
        setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                changeText();
            }
        });
    }
}
 

activity_main.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"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <com.example.day03_demo01.view.CustomView
        android:id="@+id/customview"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        android:textSize="40sp"
        />

</android.support.constraint.ConstraintLayout>
 

MainActivity中不需要寫東西

以下是效果圖 點選text 背景顏色變換  隨機數變化