xml中使用属性

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto" //自动查找
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical">
    <CustomView 
        android:layout_width="match_parent"
        android:layout_height="60dp"
        app:line_color=""
    />
</RelativeLayout>

public class CustomView extends View {

    public DottedLineView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        // 根据Style拿到TypedArray
        TypedArray array = getContext().obtainStyledAttributes(attrs, R.styleable.ExEditText);
        mLineColor = array.getColor(R.styleable.ExEditText_line_color, getResources().getColor(R.color.Red));
        mLineStrokeHeight = array.getDimension(R.styleable.ExEditText_line_stroke_height, dp2px(getContext(), 1));
        array.recycle();
    }
}

canvas.drawColor(Color.BLACK);
canvas.drawColor(Color.parse("#88880000"); // 半透明红色
canvas.drawRGB(100, 200, 100);
canvas.drawARGB(100, 100, 200, 100);

/**
前两个参数 centerX centerY 是圆心的坐标，第三个参数 radius 是圆的半径，单位都是像素
*/
drawCircle(float centerX, float centerY, float radius, Paint paint) 

canvas.drawCircle(300, 300, 200, paint);

setColor(int color)

paint.setColor(Color.parseColor("#009688"));
canvas.drawRect(30, 30, 230, 180, paint);


setARGB(int a, int r, int g, int b)

paint.setARGB(100, 255, 0, 0);
canvas.drawRect(0, 0, 200, 200, paint);