电话簿中字母导航栏切换listView内容效果

今天用到了这个功能，看了一下。在此记录一下。
一、首先记录一下本人今天所了解的新知识。
1、listview.getHeaderViewsCount (int position,int padding) 作用是设置ListView选中的位置，把当前position 的Item置顶，同时在Y轴设置一个偏移量（padding值）
2、invalidate(); 看一下源码

/**
     * Invalidate the whole view. If the view is visible,
     * {@link #onDraw(android.graphics.Canvas)} will be called at some point in
     * the future.
     * <p>
     * This must be called from a UI thread. To call from a non-UI thread, call
     * {@link #postInvalidate()}.
     */
    public void invalidate() {
        invalidate(true);
    }

意思大概是：如果这个控件可获得，那就使这个View无效。这样接下来onDraw(Canvas canvas) 会执行

下面贴出 自定义控件的代码：

ublic class QuickAlphabeticBar extends ImageButton {
    private static final String TAG = "QuickAlphabeticBar";
    private TextView mDialogText;//用于显示选中的字幕
    private Handler mHandler;
    private ListView mList;  //显示联系人的LIstView
    private float mHight;
    private String[] letters = 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" };
    private HashMap<String, Integer> alphaIndexer;

    public QuickAlphabeticBar(Context context) {
        super(context);
    }

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

    public QuickAlphabeticBar(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    public void init(TextView mDialogText) {
        this.mDialogText=mDialogText;
        mDialogText.setVisibility(View.INVISIBLE);
        mHandler = new Handler();
    }

    public void setListView(ListView mList) {
        this.mList = mList;
    }

    public void setAlphaIndexer(HashMap<String, Integer> alphaIndexer) {
        this.alphaIndexer = alphaIndexer;
    }

    public void setHight(float mHight) {
        this.mHight = mHight;
    }
    public float getHight(){
        return mHight;
    }
    float downX = 0, downY = 0, moveX = 0, moveY = 0;
    int sumMove = 0;
    @Override
    public boolean onTouchEvent(MotionEvent event) {

        int act = event.getAction();
        float x = event.getX();
        float y = event.getY();

        final int oldChoose = choose;
        // 
        int selectIndex = (int) (y / (mHight / letters.length));

        if (selectIndex > -1 && selectIndex < letters.length) {
            String key = letters[selectIndex];
            if (alphaIndexer.containsKey(key)) {
                int pos = alphaIndexer.get(key);
                if (mList.getHeaderViewsCount() > 0) {
                    this.mList.setSelectionFromTop(
                            pos + mList.getHeaderViewsCount(), 0);
                } else {
                    this.mList.setSelectionFromTop(pos, 0);
                }
                mDialogText.setText(letters[selectIndex]);
            }
        }
        switch (act) {
        case MotionEvent.ACTION_DOWN:
            sumMove = 0;
            showBkg = true;
            downX = x;
            downY = y;
            if (oldChoose != selectIndex) {
                if (selectIndex >= 0 && selectIndex < letters.length) {
                    choose = selectIndex;
                    invalidate();
                }
            }
            showDialogText();
            CLog.i(TAG, "=======================================");
            break;
        case MotionEvent.ACTION_MOVE:
            Log.e(TAG,"Move==>y:"+y);
            sumMove ++;
            moveX = x;
            moveY = y;
            if(downX != 0 && downY != 0){
                double moveAngle = getAngle(downX, moveX, downY, moveY);
                CLog.i(TAG , " move angle = " + moveAngle + ",downX = " + downX + ",downY = " + downY + ",moveX = " + moveX + ",moveY = " + moveY);
                if(sumMove < 10 && moveAngle < 0.5){
                    hideDialogText();
                    break;
                }
            }

            if (oldChoose != selectIndex) {
                if (selectIndex > 0 && selectIndex < letters.length) {
                    choose = selectIndex;
                    invalidate();//重新绘图
                }
            }

            break;
        case MotionEvent.ACTION_UP:
            showBkg = false;
            choose = -1;
            hideDialogText();
            break;
        default:
            break;
        }

        return super.onTouchEvent(event);
    }

    /**
     * 获取当前左移的角度
     * @param downX
     * @param moveX
     * @param downY
     * @param moveY
     */
    private double getAngle(float downX, float moveX, float downY, float moveY){
        float disX = downX - moveX;
        float disY = Math.abs(downY - moveY);
        if(disX == 0)
            return 10000;
        return Math.atan(disY/disX);
    }
    /**
     * 隐藏提示控件
     */
    private void hideDialogText(){
        if (mHandler != null) {
            mHandler.post(new Runnable() {
                @Override
                public void run() {
                    if (mDialogText != null
                            && mDialogText.getVisibility() == View.VISIBLE) {
                        mDialogText.setVisibility(INVISIBLE);
                    }
                }
            });
        }
    }

    /**
     * 展示提示控件
     */
    private void showDialogText(){
        if (mHandler != null) {
            mHandler.post(new Runnable() {
                @Override
                public void run() {
                    if (mDialogText != null
                            && mDialogText.getVisibility() == View.INVISIBLE) {
                        mDialogText.setVisibility(VISIBLE);
                    }
                }
            });
        }
    }

    //TODO:
    Paint paint = new Paint();
    boolean showBkg = false;
    int choose = -1;

    protected void onDraw(Canvas canvas) {//绘制字母导航栏
        super.onDraw(canvas);
        Log.e(TAG,"Ondraw==>go");

        int height = getHeight();
        int width = getWidth();
        int singleHeight = height / letters.length;
        for (int i = 0; i < letters.length; i++) {
            paint.setColor(getResources().getColor(R.color.text_title));//默认颜色
            paint.setTextSize(30);
            paint.setTypeface(Typeface.DEFAULT_BOLD);
            paint.setAntiAlias(true);
            if (i == choose) {//如果是当前选中的则设置颜色
                paint.setColor(getResources().getColor(R.color.default_quick_alpha));//选中的颜色
                paint.setFakeBoldText(true);
            }
            float xPos = width / 2 - paint.measureText(letters[i]) / 2;
            float yPos = singleHeight * i + singleHeight;
            canvas.drawText(letters[i], xPos, yPos, paint);
            paint.reset();
        }

    }
    public void setLetters(String[] letters){
        this.letters = letters;
        postInvalidate();
    }
}

此时我们一般还需要获取系统通讯录...下次再说。