<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res/com.gaoyuan4122.customui"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >
    <TextView
        android:id="@+id/tv_hello"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />
    <com.gaoyuan4122.customui.views.CustomView1
        android:id="@+id/cv_custom1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/tv_hello" />
    
    <TextView
        android:id="@+id/tv_hello2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world"
        android:layout_below="@id/cv_custom1" />
    <com.gaoyuan4122.customui.views.CustomView2
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/tv_hello2"
        app:backgroundColor="#ff00ff"
        app:textColor="#ffff00" />
</RelativeLayout>

    private int mTextColor;
    private int mBackgroundColor;
    public CustomView2(Context context) {
        this(context, null);
    }
    public CustomView2(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }
    // 自定义属性会被封装到 attrs 中, 第三个参数和样式有关, 这里先不说.
    public CustomView2(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        // 通过下面的方法去除自定义属性
        TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.CustomView2);
        mTextColor = typedArray.getColor(R.styleable.CustomView2_textColor, Color.RED);
        mBackgroundColor = typedArray.getColor(R.styleable.CustomView2_backgroundColor, Color.BLUE);
        // 最后一定要注意调用这个方法, 至于为什么后面会说.
        typedArray.recycle();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        mPaint.setStyle(Style.FILL);
        mPaint.setColor(mBackgroundColor);
        mRect.set(0, 0, 100, 100);
        canvas.drawRect(mRect, mPaint);
        mPaint.setColor(mTextColor);
        mPaint.setTextSize(30.0f);
        canvas.drawText("Hello!", 0, 100, mPaint);
    }