Android ListView A~Z快速索引（改进版）

上一篇文章虽然实现了ListView 快速索引的效果，但是有一个小小的Bug。这个Bug我在前面也说了，这篇文章就来解决这个Bug。

我研究的时候发现只要showBg值为true，中间的字母就显示，而当showBg 的值为false的时候中间的字母就可以消失。只要SlideBar的状态为ACTION_DOWN和ACTION_MOVE 的时候showBg的值为true，而ACTION_UP的时候showBg的值就为false；

所以根据上面这个特征，我们只要把OnToucheLetterChange()这个回调函数的参数改一下就可以了。改成onTouchLetterChange(boolean isTouched, String s) 

boolean类型的参数直接把showBg传过去就可以了。

改进后的代码如下：

package com.folyd.tuan.view;

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

/**
 * 自定义的View，实现ListView A~Z快速索引效果
 * 
 * @author Folyd
 * 
 */
public class SlideBar extends View {
	private Paint paint = new Paint();
	private OnTouchLetterChangeListenner listenner;
	// 是否画出背景
	private boolean showBg = false;
	// 选中的项
	private int choose = -1;
	// 准备好的A~Z的字母数组
	public static String[] letters = { "#", "A", "B", "C", "D", "E", "F", "G",
			"H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T",
			"U", "V", "W", "X", "Y", "Z" };

	// 构造方法
	public SlideBar(Context context) {
		super(context);
	}

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

	@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);
		// 获取宽和高
		int width = getWidth();
		int height = getHeight();
		// 每个字母的高度
		int singleHeight = height / letters.length;
		if (showBg) {
			// 画出背景
			canvas.drawColor(Color.parseColor("#55000000"));
		}
		// 画字母
		for (int i = 0; i < letters.length; i++) {
			paint.setColor(Color.BLACK);
			// 设置字体格式
			paint.setTypeface(Typeface.DEFAULT_BOLD);
			paint.setAntiAlias(true);
			paint.setTextSize(20f);
			// 如果这一项被选中，则换一种颜色画
			if (i == choose) {
				paint.setColor(Color.parseColor("#F88701"));
				paint.setFakeBoldText(true);
			}
			// 要画的字母的x,y坐标
			float posX = width / 2 - paint.measureText(letters[i]) / 2;
			float posY = i * singleHeight + singleHeight;
			// 画出字母
			canvas.drawText(letters[i], posX, posY, paint);
			// 重新设置画笔
			paint.reset();
		}
	}

	/**
	 * 处理SlideBar的状态
	 */
	@Override
	public boolean dispatchTouchEvent(MotionEvent event) {
		final float y = event.getY();
		// 算出点击的字母的索引
		final int index = (int) (y / getHeight() * letters.length);
		// 保存上次点击的字母的索引到oldChoose
		final int oldChoose = choose;
		switch (event.getAction()) {
		case MotionEvent.ACTION_DOWN:
			showBg = true;
			if (oldChoose != index && listenner != null && index > 0
					&& index < letters.length) {
				choose = index;
				listenner.onTouchLetterChange(showBg, letters[index]);
				invalidate();
			}
			break;

		case MotionEvent.ACTION_MOVE:
			if (oldChoose != index && listenner != null && index > 0
					&& index < letters.length) {
				choose = index;
				listenner.onTouchLetterChange(showBg, letters[index]);
				invalidate();
			}
			break;
		case MotionEvent.ACTION_UP:
			showBg = false;
			choose = -1;
			if (listenner != null) {
				if (index <= 0) {
					listenner.onTouchLetterChange(showBg, "A");
				} else if (index > 0 && index < letters.length) {
					listenner.onTouchLetterChange(showBg, letters[index]);
				} else if (index >= letters.length) {
					listenner.onTouchLetterChange(showBg, "Z");
				}
			}
			invalidate();
			break;
		}
		return true;
	}

	/**
	 * 回调方法，注册监听器
	 * 
	 * @param listenner
	 */
	public void setOnTouchLetterChangeListenner(
			OnTouchLetterChangeListenner listenner) {
		this.listenner = listenner;
	}

	/**
	 * SlideBar 的监听器接口
	 * 
	 * @author Folyd
	 * 
	 */
	public interface OnTouchLetterChangeListenner {

		void onTouchLetterChange(boolean isTouched, String s);
	}

}

Activity中就很容易处理了：

mSlideBar
				.setOnTouchLetterChangeListenner(new OnTouchLetterChangeListenner() {

					@Override
					public void onTouchLetterChange(boolean isTouched, String s) {

						float_letter.setText(s);
						if (isTouched) {
							float_letter.setVisibility(View.VISIBLE);
						} else {
							float_letter.postDelayed(new Runnable() {

								@Override
								public void run() {
									float_letter.setVisibility(View.GONE);
								}
							}, 100);
						}
						int position = array.indexOf(s);
						mListView.setSelection(position);
					}
				});

这样就解决Bug了。哈哈。