自定义控件，开关左右滑动

自定义控件一般的思路都是根据图片，自己绘制相应的控件

布局文件

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <com.itheima27.slidebutton.view.SlideButton
        android:id="@+id/slidebutton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true" />

</RelativeLayout>

import com.itheima27.slidebutton.R;
import com.itheima27.slidebutton.interf.OnToggleStateChangedListener;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class SlideButton extends View {

    private Bitmap switchBG;    // 滑动开关的背景
    private Bitmap slideButtonBG; // 滑动块的背景
    private boolean currentState = false;    // 开关当前的状态, 默认为: 关闭
    private int currentX;    // x轴的偏移量
    private boolean isSliding = false;        // 是否正在滑动中
    private OnToggleStateChangedListener mListener;

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

    /**
     * 当测量当前控件的宽高时回调
     */
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        
        // 设置开关的宽和高
        setMeasuredDimension(switchBG.getWidth(), switchBG.getHeight());
    }

    /**
     * 绘制当前控件的方法
     */
    @Override
    protected void onDraw(Canvas canvas) {
        
        // 1. 把滑动开关的背景画到画布上
        canvas.drawBitmap(switchBG, 0, 0, null);        // 把背景平铺到控件上
        
        // 2. 绘制滑动块显示的位置, 开或者关
        
        if(isSliding) {
            int left = currentX - (slideButtonBG.getWidth() / 2);
            if(left < 0) {
                left = 0;
            } else if(left > switchBG.getWidth() - slideButtonBG.getWidth()) {
                left = switchBG.getWidth() - slideButtonBG.getWidth();
            }
            
            canvas.drawBitmap(slideButtonBG, left, 0, null);
        } else {
            if(currentState) {    // 绘制开关为开的状态
                canvas.drawBitmap(slideButtonBG, switchBG.getWidth() - slideButtonBG.getWidth(), 0, null);
            } else {    // 绘制开关为关的状态
                canvas.drawBitmap(slideButtonBG, 0, 0, null);
            }
        }
        super.onDraw(canvas);
    }

    /**
     * 当产生触摸时间时回调此方法
     */
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN: // 按下
            currentX = (int) event.getX();
            isSliding  = true;
            break;
        case MotionEvent.ACTION_MOVE: // 移动
            currentX = (int) event.getX();
            break;
        case MotionEvent.ACTION_UP: // 抬起
            isSliding = false;
            
            // 判断当前滑动块, 偏向于哪一边, 如果滑动块的中心点小于背景的中心点, 设置为关闭状态
            
            int bgCenter = switchBG.getWidth() / 2;
            
            boolean state = currentX > bgCenter;        // 改变后的状态
            
            // 调用用户的监听事件
            if(state != currentState && mListener != null) {
                mListener.onToggleStateChanged(state);
            }

            currentState = state;
            break;
        default:
            break;
        }

        invalidate();        // 刷新当前控件, 会引起onDraw方法的调用
        return true;
    }

    /**
     * 初始化图片
     */
    private void initBitmap() {
        slideButtonBG = BitmapFactory.decodeResource(getResources(), R.drawable.slide_button_background);
        switchBG = BitmapFactory.decodeResource(getResources(), R.drawable.switch_background);
    }

    /**
     * 设置开关的状态
     * @param b
     */
    public void setToggleState(boolean b) {
        currentState = b;
    }

    /**
     * 设置开关状态改变的监听事件
     * @param listener
     */
    public void setOnToggleStateChangedListener(OnToggleStateChangedListener listener) {
        this.mListener = listener;
    }
}