Android自定义View用切图显示字符串

public class DigitalTextView extends LinearLayout {

  public DigitalTextView(Context context) {
    super(context);
    init();
  }

  public DigitalTextView(Context context, AttributeSet attrs) {
    super(context, attrs);
    init();
  }

  // 初始化
  private void init() {
    this.setOrientation(LinearLayout.HORIZONTAL);
  }
  /**
   * 获取调频图片
   *
   * @param index 频率值
   * @return 对应频率值的图片id
   */
  private int getFreqDrawable(int index) {
    int drawableId = -1;
    switch (index) {
      case 0:
        drawableId = R.drawable.num_0;
        break;
      case 1:
        drawableId = R.drawable.num_1;
        break;
      case 2:
        drawableId = R.drawable.num_2;
        break;
      case 3:
        drawableId = R.drawable.num_3;
        break;
      case 4:
        drawableId = R.drawable.num_4;
        break;
      case 5:
        drawableId = R.drawable.num_5;
        break;
      case 6:
        drawableId = R.drawable.num_6;
        break;
      case 7:
        drawableId = R.drawable.num_7;
        break;
      case 8:
        drawableId = R.drawable.num_8;
        break;
      case 9:
        drawableId = R.drawable.num_9;
        break;
    }
    return drawableId;
  }

  /**
   * 根据传递进来的字符，返回对应的图片资源
   *
   * @param c 传递进来的字符
   * @return 对应的图片id
   */
  private int getResourceForChar(char c) {
    if (c == '.') {
      return R.drawable.num_dot;
    } else if (c >= '0' && c <= '9') {
      return getFreqDrawable(c - '0');
    } else {
      return -1;
    }
  }

  // 创建一个ImageView
  private ImageView createImageView() {
    ImageView imageView = new ImageView(getContext());
    LayoutParams param = new LayoutParams(
        LinearLayout.LayoutParams.WRAP_CONTENT,
        LinearLayout.LayoutParams.WRAP_CONTENT);
    imageView.setLayoutParams(param);
    return imageView;
  }


  /**
   * 更新自定义TextView
   * @param text 传递进来的字符串
   */
  public void setDigitalText(String text) {

    int startIndex = getChildCount() - text.length();// 起始位置，因为imageView的数量是根据字符串的长度创建的
    if (startIndex < 0)//第一次更新的时候肯定是小于0的
      startIndex = 0;

    for (int i = 0; i < startIndex; i++) {
      getChildAt(i).setVisibility(View.GONE);
    }

    //下面是根据字符串的长度，循环更换为对应的图片
    for (int i = 0; i < text.length(); i++) {
      int childId = i + startIndex;
      int resId = getResourceForChar(text.charAt(i));//将每个字符转换为数字

      if (resId != -1) {
        if (childId == getChildCount()) {
          addView(createImageView());//添加到LinearLayout中
        }
        ImageView child = ((ImageView) getChildAt(childId));
        child.setVisibility(View.VISIBLE);
        child.setImageResource(resId);
      }
    }
  }
}