Android Custom View for fast indexing

Foreword

Look at the effect of it ~

Function Point Analysis difficult to achieve

analysis:

Assumptions: average height of the control block is divided into 26, and the width of the control block of the same width.

Assumptions: Each letter is a square cell welt package. Centered within the cell block.

Each letter coordinates (X axis, Y axis) is the bottom left corner position, i.e. the position of the lower left corner of the cell.

In Case A: index 0
x coordinate: a float x = 0.5f the measuredWidth * - * the textWidth 0.5f (half the width of the control - half the width of the cell)
Y-axis coordinate: a float 0.5f + Y = cellHeight the textWidth * 0.5 * f (+ half the width of the cell is half the width of the control)

In Case B: Index 1
x coordinate: a float the measuredWidth * x = 0.5f - (half the width of the control - half the width of the cell) the textWidth * 0.5f
Y-axis coordinate: a float 0.5f + Y = cellHeight the textWidth * 0.5 * f + i * cellHeight (half of the half width of the cell control + width + front of all the height of the cell)

Description: the measuredWidth - the entire width of the custom control; cellHeight - height of the cell; textWidth - single letter width (available through the brush)

26 letters of the drawing, and the position of each letter
of the code sample (also refer to the specific implementation Demo)

//绘制 A-Z
for (int i = 0; i < LETTERS.length; i++) {
    String letter = LETTERS[i];
    //计算每个字母的坐标位置，通过画笔可以获取字母的宽度：measureText()
    float x = cellWidth * 0.5f - paint.measureText(letter) * 0.5f;
    //获取指定字符串指定区域的宽高信息
    Rect rect = new Rect();
    paint.getTextBounds(letter, 0, letter.length(), rect);
    //获取字母的高度
    int textHeight = rect.height();
    //获取字母的宽度 和 paint.measureText(letter) 结果一样
    //int textWidth = rect.width();
    float y = cellHeight * 0.5f + textHeight * 0.5f + i * cellHeight;

    //【改变选择字母】字母被选中时，重绘字母时，改变字母状态
    paint.setColor(i == currentIndex ? Color.GRAY : Color.WHITE);

    canvas.drawText(letter, x, y, paint);
}

When generating a touch event, determine the selected position

  private void getCurrentIndex(MotionEvent event) {
        //获取当前所处位置的-Y轴-坐标（取值可能会小于0）
        float y = event.getY();
        //得到当前触摸位置是第几个索引位置
        int index = (int) (y / cellHeight);
        //获取当前索引和上次获取索引对比，相同则不处理
        if (index != currentIndex) {
            if (index >= 0 && index < LETTERS.length) {
                currentIndex = index;
                //设置一个监听回调：返回当前被选中的字母（也可以处理其他业务）
                if (updateListener != null) {
                    updateListener.onLetterUpdate(LETTERS[index]);
                }
            }
        }
    }

Pullback in activity in the listener, and the combination of custom controls and listView

    @Override
    public void onLetterUpdate(String letter) {
        showCustomToast(letter); //自定义的一个Toast(可以查看Demo)
        //触摸监听回调
        //找到数据集合中首次出现letter的索引位置，listView直接跳到该索引位置
        for (int index = 0; index < persons.size(); index++) {
            String pin = persons.get(index).getNamePinYin().charAt(0) + "";
            if (TextUtils.equals(pin, letter)) {
                listView.setSelection(index);
                break;
            }
        }
    }

PS: Well, here, a simple custom fast indexing function is realized. I am pleased to share with you here and learn from each other.

Android Custom View for fast indexing

Foreword

Function Point Analysis difficult to achieve

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