Android开发实现根据字母快速定位侧边栏

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);
	}

}
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