按首字母对List排列，并根据首字母快速定位的实现，在Android开发中被大量应用，今天我也来亲自实现一下，将这个控件封装起来，也方便以后的使用。大体上可以分为两步来实现这个控件：首先使自己的控件继承于View，并进行图形绘制；然后根据触摸位置计算当前触摸的字母，并实现回调接口的方法。
下面来进行实践：
1.创建自己的控件类并继承于View，注意：不能只声明含有一个构造参数Context的构造函数，这样我们的控件无法在xml文件中调用，因为Android中xml调用控件之间的参数传递是通过构造参数中的AttributeSet参数来进行的，没有这个参数我们的控件不能在xml中使用。在这里我添加了父类View的三个构造函数，这里只需要调用父类的构造函数即可，不需要额外的操作。
public QuicLocationBar(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
// TODO Auto-generated constructor stub
}
public QuicLocationBar(Context context, AttributeSet attrs) {
super(context, attrs);
// TODO Auto-generated constructor stub
}
public QuicLocationBar(Context context) {
super(context);
// TODO Auto-generated constructor stub
}
2.绘制字符：绘制的部分通过复写父类的onDraw方法来实现，并通过Paint来来绘制
1）首先声明一个成员变量来保存我们的字符数组，并初始化一个Paint类的成员变量来帮助我们绘制字符
private String characters[] = { "#", "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" };
private Paint paint = new Paint();
2）根据总的高度除以字符串数组的长度来得到每一个字符的高度，然后循环遍历整个数组来绘制字符
@Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);
int width = getWidth();
int height = getHeight();
int singleHeight = height / characters.length;
for (int i = 0; i < characters.length; i++) {
//对paint进行相关的参数设置
paint.setColor(getResources().getColor(R.color.myblack));
paint.setTypeface(Typeface.DEFAULT_BOLD);
paint.setAntiAlias(true);
paint.setTextSize(20);
if (i == choose) {//choose变量表示当前触摸的字符位置，若没有触摸则为-1
paint.setColor(getResources().getColor(R.color.myred));
paint.setFakeBoldText(true);
}
//计算字符的绘制的位置
float xPos = width / 2 - paint.measureText(characters[i]) / 2;
float yPos = singleHeight * i + singleHeight;
//在画布上绘制字符
canvas.drawText(characters[i], xPos, yPos, paint);
paint.reset();//每次绘制完成后不要忘记重制Paint
}
}
注意：不要忘记在每次绘制完成后重置Paint
3.处理触摸事件：通过复写父类的dispatchTouchEvent方法来实现
1）首先我们要设计一个回调接口，当我们触摸的字符发生改变时可以执行该回调接口的方法
public interface OnTouchLetterChangedListener {
public void touchLetterChanged(String s);
}
2）当发生按下事件或移动事件时，我们根据触摸点的位置计算出当前触摸的字符，如果和我们显示的字符不相同则执行回调接口的方法，并进行View的重绘；当发生抬起事件时我们将当前显示的字符更新为-1，表示当前没有字符显示，并进行View的重绘。
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
int action = event.getAction();
float y = event.getY();
int c = (int) (y / getHeight() * characters.length);
switch (action) {
case MotionEvent.ACTION_UP:
choose = -1;//
setBackgroundColor(0x0000);
invalidate();
break;
case MotionEvent.ACTION_DOWN:
case MotionEvent.ACTION_MOVE:
setBackgroundColor(getResources().getColor(R.color.darkgray));
if (choose != c) {
if (c >= 0 && c < characters.length) {
if (mOnTouchLetterChangedListener != null) {
mOnTouchLetterChangedListener
.touchLetterChanged(characters[c]);
}
choose = c;
invalidate();
}
}
break;
}
return true;//返回true表示触摸事件不在向下分发
}
附上整体源码：
package com.example.test.widget;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Typeface;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.widget.TextView;
import com.example.gymapp.R;
public class QuicLocationBar extends View {
private String characters[] = { "#", "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" };
private int choose = -1;
private Paint paint = new Paint();
private OnTouchLetterChangedListener mOnTouchLetterChangedListener;
public QuicLocationBar(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
// TODO Auto-generated constructor stub
}
public QuicLocationBar(Context context, AttributeSet attrs) {
super(context, attrs);
// TODO Auto-generated constructor stub
}
public QuicLocationBar(Context context) {
super(context);
// TODO Auto-generated constructor stub
}
public void setOnTouchLitterChangedListener(
OnTouchLetterChangedListener onTouchLetterChangedListener) {
this.mOnTouchLetterChangedListener = onTouchLetterChangedListener;
}
@Override
protected void onDraw(Canvas canvas) {
// TODO Auto-generated method stub
super.onDraw(canvas);
int width = getWidth();
int height = getHeight();
int singleHeight = height / characters.length;
for (int i = 0; i < characters.length; i++) {
// 对paint进行相关的参数设置
paint.setColor(getResources().getColor(R.color.myblack));
paint.setTypeface(Typeface.DEFAULT_BOLD);
paint.setAntiAlias(true);
paint.setTextSize(20);
if (i == choose) {// choose变量表示当前显示的字符位置，若没有触摸则为-1
paint.setColor(getResources().getColor(R.color.myred));
paint.setFakeBoldText(true);
}
// 计算字符的绘制的位置
float xPos = width / 2 - paint.measureText(characters[i]) / 2;
float yPos = singleHeight * i + singleHeight;
// 在画布上绘制字符
canvas.drawText(characters[i], xPos, yPos, paint);
paint.reset();// 每次绘制完成后不要忘记重制Paint
}
}
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
int action = event.getAction();
float y = event.getY();
int c = (int) (y / getHeight() * characters.length);
switch (action) {
case MotionEvent.ACTION_UP:
choose = -1;//
setBackgroundColor(0x0000);
invalidate();
break;
case MotionEvent.ACTION_DOWN:
case MotionEvent.ACTION_MOVE:
setBackgroundColor(getResources().getColor(R.color.darkgray));
if (choose != c) {
if (c >= 0 && c < characters.length) {
if (mOnTouchLetterChangedListener != null) {
mOnTouchLetterChangedListener
.touchLetterChanged(characters[c]);
}
choose = c;
invalidate();
}
}
break;
}
return true;
}
public interface OnTouchLetterChangedListener {
public void touchLetterChanged(String s);
}
}