41右侧字母索引栏的编写

实现的效果图：

通过自定义View，然后在xml文件中引用可以达到需求。

public SiderBar(Context context, AttributeSet attrs) {
		super(context, attrs);
		this.context = context;
		init();
	}

	private String[] sections = new String[]{"搜","#","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 void init(){
		paint = new Paint(Paint.ANTI_ALIAS_FLAG);
		paint.setColor(Color.DKGRAY);
		paint.setTextAlign(Align.CENTER);
		paint.setTextSize(DensityUtil.sp2px(context, 10));
	}

首先使用带有两个参数的构造器，然后初始化数组和初始化画笔。

在onDraw方法中，“写出”每个字母的值：

@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);
		float center = getWidth() / 2;
		height = getHeight() / sections.length;
		for (int i = sections.length - 1; i > -1; i--) {
			canvas.drawText(sections[i], center, height * (i+1), paint);
		}
	}

宽度是这个View的宽度的一般，每个高度是View的总高度除以数组的长度（每个字母的高度就确定了），这样就“写上”了每个字母。

接下来的sectionForPoint实现每个数组元素的索引，如下：

private int sectionForPoint(float y) {
		
		
		
		LogUtil.d(TAG, "y :" + y + "");
		LogUtil.d(TAG, "height :" + height + "");
		
		
		int index = (int) (y / height);
		LogUtil.d(TAG, "index :" + index + "");
		if(index < 0) {
			index = 0;
		}
		if(index > sections.length - 1){
			LogUtil.d(TAG, "sections.length - 1:" + (sections.length - 1) + "");
			index = sections.length - 1;
		}
		return index;
	}

整个View的高度不变：

需要考虑下边界的问题。

接着在onTouchEvent处理响应的四个事件，按下，抬起，滑动，取消。

@Override
	public boolean onTouchEvent(MotionEvent event) {
		switch (event.getAction()) {
		case MotionEvent.ACTION_DOWN:{
			if(header == null){
				header = (TextView) ((View)getParent()).findViewById(R.id.floating_header);
			}
			setHeaderTextAndscroll(event);
			header.setVisibility(View.VISIBLE);
			setBackgroundResource(R.drawable.sidebar_background_pressed);
			return true;
		}
		case MotionEvent.ACTION_MOVE:{
			setHeaderTextAndscroll(event);
			return true;
		}
		case MotionEvent.ACTION_UP:
			header.setVisibility(View.INVISIBLE);
			setBackgroundColor(Color.TRANSPARENT);
			return true;
		case MotionEvent.ACTION_CANCEL:
			header.setVisibility(View.INVISIBLE);
			setBackgroundColor(Color.TRANSPARENT);
			return true;
		}
		return super.onTouchEvent(event);
	}

private void setHeaderTextAndscroll(MotionEvent event){
		 if (mListView == null) {
		        //check the mListView to avoid NPE. but the mListView shouldn't be null
		        //need to check the call stack later
		        return;
		    }
		String headerString = sections[sectionForPoint(event.getY())];
		LogUtil.d(TAG, " event.getY():" + event.getY());
		header.setText(headerString);
		ContactAdapter adapter = (ContactAdapter) mListView.getAdapter();
		String[] adapterSections = (String[]) adapter.getSections();
		try {
			for (int i = adapterSections.length - 1; i > -1; i--) {
				if(adapterSections[i].equals(headerString)){
					mListView.setSelection(adapter.getPositionForSection(i));
					break;
				}
			}
		} catch (Exception e) {
			LogUtil.d(TAG, e.getMessage());
		}
		
	}