先看看效果图

字母选择

1.自定义 View 的基本流程

• 创建 View Class
• 创建 attr 属性文件，确定属性
• View Class 绑定 attr 属性
• onMeasure 测量
• onDraw 绘制
• onTouchEvent ( 用户交互需要处理 )

1.1 创建 View Class

public class LetterSideView extends View {
    public LetterSideView(Context context) {
        this(context, null);
    }

    public LetterSideView(Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public LetterSideView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }
}

1.2 创建 attr

<declare-styleable name="LetterSideView">
    <!--默认颜色-->
    <attr name="normalColor" format="color"/>
    <!--选中颜色-->
    <attr name="focusColor" format="color"/>
    <!--文字大小-->
    <attr name="letterSize" format="dimension"/>
</declare-styleable>

1.3 绑定 attr

private void initAttr(Context context, AttributeSet attrs) {
    TypedArray array = context.obtainStyledAttributes(attrs, R.styleable.LetterSideView);
    //默认颜色
    mNormalColor = array.getColor(R.styleable.LetterSideView_normalColor, mNormalColor);
    //选中颜色
    mFocusColor = array.getColor(R.styleable.LetterSideView_focusColor, mFocusColor);
    //文字大小
    mTextSize = array.getDimensionPixelSize(R.styleable.LetterSideView_letterSize, sp2px(mTextSize));
    //回收
    array.recycle();
}

1.4 onMeasure

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    //字母宽度
    int letterWidth = getTextWidth("W");
    //宽
    int width = getPaddingLeft() + getPaddingRight() + letterWidth;
    //高
    int height = MeasureSpec.getSize(heightMeasureSpec);
    //设置宽高
    setMeasuredDimension(width, height);
}

1.5 onDraw

protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    //每个字母的高度
    int item = (getHeight() - getPaddingTop() - getPaddingBottom()) / letter.length;
    for (int i = 0; i < letter.length; i++) {
        //每个字母的中心位置
        int letterYCenter = item / 2 + i * item + getPaddingTop();
        Paint.FontMetricsInt fontMetricsInt = mNormalPaint.getFontMetricsInt();
        int x = getWidth() / 2 - getTextWidth(letter[i]) / 2;
        int y = (fontMetricsInt.bottom - fontMetricsInt.top) / 2 - fontMetricsInt.bottom;
        int baseLine = letterYCenter + y;
        if (letter[i].equals(currentLetter)) {
            canvas.drawText(letter[i], x, baseLine, mFocusPaint);
        } else {
            canvas.drawText(letter[i], x, baseLine, mNormalPaint);
        }
    }
}

1.6 onTouchEvent

public boolean onTouchEvent(MotionEvent event) {
    switch (event.getAction()) {
        case MotionEvent.ACTION_UP:
            letterCallBack.letterCallBack(currentLetter, false);
            break;
        case MotionEvent.ACTION_MOVE:
            //获取当前 Y 位置
            float currentY = event.getY();
            int item = (getHeight() - getPaddingTop() - getPaddingBottom()) / letter.length;
            int currentPosition = (int) currentY / item;
            if (currentPosition < 0) {
                currentPosition = 0;
            }

            if (currentPosition > letter.length - 1) {
                currentPosition = letter.length - 1;
            }

            if (letter[currentPosition].equals(currentLetter)) {
                return true;
            }

            currentLetter = letter[currentPosition];

            if (letterCallBack != null) {
                letterCallBack.letterCallBack(currentLetter, true);
            }

            invalidate();
            break;
    }
    return true;
}

自定义字母选择就介绍到这里了，如果有什么写得不对的，可以在下方评论留言，我会第一时间改正。

Github 源码链接