サンプルとして簡易TextViewを作ってみました。

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:orientation="vertical"
              android:layout_width="fill_parent"
              android:layout_height="fill_parent"
        >
    <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:text="Hello World, MyActivity"
            />
    <com.example.MyTextView xmlns:app="http://hoge/app"
                            android:layout_width="wrap_content"
                            android:layout_height="wrap_content"
                            app:text="Hello MyTextView."
                            app:textSize="48"
                            app:textColor="#FFFF0000"
                            app:background="#FFFFFFFF"/>

</LinearLayout>

MyTextView.java

package com.example;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;

public class MyTextView extends View {
    private static final int BACKGROUND_COLOR = 0;
    private static final int TEXT_COLOR=Color.WHITE;
    private static final int TEXT_SIZE = 12;
    private String text="no data";
    private Paint paint;

    public MyTextView(Context context) {
        super(context);
        paint=makePaint(TEXT_COLOR, TEXT_SIZE);
        setBackgroundColor(BACKGROUND_COLOR);
    }

    public MyTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        final String NAME_SPACE = "http://hoge/app";
        text=attrs.getAttributeValue(NAME_SPACE,"text");
        int fontColor = attrs.getAttributeIntValue(NAME_SPACE, "textColor", TEXT_COLOR);
        setBackgroundColor(attrs.getAttributeIntValue(NAME_SPACE,"background",BACKGROUND_COLOR));
        paint=makePaint(fontColor,(attrs.getAttributeIntValue(NAME_SPACE,"textSize",TEXT_SIZE)));
    }
    @Override
    protected void onDraw(Canvas canvas) {
        canvas.drawText(text,0,-paint.getFontMetrics().top,paint);
    }

    private Paint makePaint(int fontColor,int size) {
        Paint paint=new Paint();
        paint.setAntiAlias(true);
        paint.setTextSize(size);
        paint.setColor(fontColor);
        return paint;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int y=(int)(paint.getFontMetrics().bottom-paint.getFontMetrics().top);
        setMeasuredDimension((int) paint.measureText(text),y);
    }
}