Android 绘图进阶：Canvas绘制联系人侧滑列表(drawText+监听者模式)

　　上面展示的是效果图，我们平时使用的通过点击字母就能找到相关字母的联系人，这就是我们想要达到的效果。

思路与步骤

　　根据我们想要实现的效果，我们先要理一理思路，所有的编程都是这样，有了清晰的思路才能确定每一步我们具体要做什么。

　 首先我们想要出现手机联系人的效果，就要先绘制右侧的字母，再对屏幕的手势滑动进行监听，使字母在被点击时变色，然后是我们的布局中的TextView内容的改变，这里TextView的改变我们需要用到监听者模式。

1、绘制右侧字母

思路：使用drawtext方法循环从上到下进行绘制。

根据屏幕高度，设置字体大小

[code]//必须写在onMeasure方法中，
//如果写在构造器中，由于开始的时候没有及时获得宽高，导致高度默认为0
    mpainttext.setTextSize(height/26f);

String数组，用于循环绘制

[code]    private String[] array=new String[]{"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"};

在onDraw方法中进行绘制

[code]   for(int i=0;i<26;i++){
   //由于字母大小不一致，选择宽度最大的'm'相减，作为x轴坐标
      canvas.drawText(array[i], width-mpainttext.measureText("m"), height/26*(i+1), mpainttext);
            }

        }

2、覆写onTouchEvent方法，支持手势滑动

[code]  @Override
public boolean onTouchEvent(MotionEvent event) {

        switch (event.getAction()) {
        //ACTION_MOVE监听手指滑动
case MotionEvent.ACTION_MOVE:       
        //ACTION_DOWN监听手指落下
        case MotionEvent.ACTION_DOWN:
        //获取手指落下的x坐标与Y坐标
            x=event.getX();
            y=event.getY();
            if(x>=width-mpainttext.measureText("m")&&x<width){
            //确定点击的是第几个
                index=(int)y/(height/26);
                Log.d("touch", "点击的是"+array[index]);                
                invalidate();
                return true;
            }
            break;
            //ACTION_UP监听手指抬起
case MotionEvent.ACTION_UP:

    return true;

        default:
            break;

    }

    return super.onTouchEvent(event);
}

3、实现点击字体颜色改变

使用index作为判断

[code]  private int index=-1;

//设置画笔

[code]//创建新画笔，设置画笔颜色
    mpaintcolor=new Paint();
        mpaintcolor.setColor(Color.RED);
        mpaintcolor.setTextAlign(Align.CENTER);

[code]//onMeasure方法中才会获得高度
    mpaintcolor.setTextSize(height/26f);

手势监听事件中进行index设置，用于后面绘制时改变颜色的判断

[code] @Override
public boolean onTouchEvent(MotionEvent event) {

        switch (event.getAction()) {
case MotionEvent.ACTION_MOVE:               
        case MotionEvent.ACTION_DOWN:
            x=event.getX();
            y=event.getY();
            if(x>=width-mpainttext.measureText("m")&&x<width){
                index=(int)y/(height/26);
                Log.d("touch", "点击的是"+array[index]);

                invalidate();
                return true;
            }
            break;
case MotionEvent.ACTION_UP:
    if(index!=-1){
        index=-1;
    }
    invalidate();
    return true;

        default:
            break;

    }

onDraw方法中根据index改变显示颜色

[code] for(int i=0;i<26;i++){

            if(index!=-1&&i==index){
                canvas.drawText(array[index], width-mpainttext.measureText("m"), height/26*(i+1), mpaintcolor); 
                index=-1;
            }else{
                canvas.drawText(array[i], width-mpainttext.measureText("m"), height/26*(i+1), mpainttext);
            }

        }

4、监听者模式

监听者模式：

（1）在被监听对象中编写接口interface，在接口中编写抽象方法，用于调用。

（2）创建被监听的对象

（3）

被监听者在继承View的class中编写接口

[code]//interface接口
    public interface OnItemSelect{
    //抽象方法
        public void OnItemSelectListener(String indexString);
    }
    //创建传递对象（）
    private  OnItemSelect OnItemSelectlistener;
    //监听者将要调用的方法
    public void OnItemSelectlistener( OnItemSelect OnItemSelectlistener){
        //监听者中调用到该方法，传递进一个OnItemSelectlistener对象
        this.OnItemSelectlistener=OnItemSelectlistener;
    }

监听者中调用

[code]这里写代码片

5、完整代码

View

[code]public class MySlider extends View{
    private int width;
    private int height;
    private Paint mpainttext;
    private Paint mpaintcolor;
    private int index=-1;
    private String[] array=new String[]{"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"};
    public MySlider(Context context) {
        super(context);

    }

    public MySlider(Context context, AttributeSet attrs) {
        super(context, attrs);
        mpainttext=new Paint();     
        mpainttext.setTextAlign(Align.CENTER);
        mpaintcolor=new Paint();
        mpaintcolor.setColor(Color.RED);
        mpaintcolor.setTextAlign(Align.CENTER);
    }
    public interface OnItemSelect{
        public void OnItemSelectListener(String indexString);
    }
    private  OnItemSelect OnItemSelectlistener;
    public void OnItemSelectlistener( OnItemSelect OnItemSelectlistener){
        this.OnItemSelectlistener=OnItemSelectlistener;
    }

    private float x;
    private float y;
   @Override
public boolean onTouchEvent(MotionEvent event) {

        switch (event.getAction()) {
case MotionEvent.ACTION_MOVE:               
        case MotionEvent.ACTION_DOWN:
            x=event.getX();
            y=event.getY();
            if(x>=width-mpainttext.measureText("m")&&x<width){
                index=(int)y/(height/26);
                Log.d("touch", "点击的是"+array[index]);
                OnItemSelectlistener.OnItemSelectListener(array[index]);
                invalidate();
                return true;
            }
            break;
case MotionEvent.ACTION_UP:
    if(index!=-1){
        index=-1;
    }
    invalidate();
    return true;

        default:
            break;

    }

    return super.onTouchEvent(event);
}
    @Override
    protected void onDraw(Canvas canvas) {

        super.onDraw(canvas);
        for(int i=0;i<26;i++){

            if(index!=-1&&i==index){
                canvas.drawText(array[index], width-mpainttext.measureText("m"), height/26*(i+1), mpaintcolor); 
                index=-1;
            }else{
                canvas.drawText(array[i], width-mpainttext.measureText("m"), height/26*(i+1), mpainttext);
            }

        }

    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        width = getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec);
        height = getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec);
        setMeasuredDimension(width, height);//告知父布局该View的大小
        //测量出来之后使用
        mpainttext.setTextSize(height/26f);
        mpaintcolor.setTextSize(height/26f);

    }
}

Activity

[code]public class MainActivity_bitmap extends Activity {
    private TextView mtextview;
    private MySlider msliderview;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.bitmap_view);
        mtextview = (TextView) findViewById(R.id.textview);
        msliderview = (MySlider) findViewById(R.id.slider);
        msliderview.OnItemSelectlistener(new OnItemSelect() {

            @Override
            public void OnItemSelectListener(String indexString) {
                mtextview.setText(indexString);

            }
        });
    }

}