package com.example.zhuang;

import android.content.Context;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.view.WindowManager;
import android.widget.Scroller;


public class MyScrollView extends ViewGroup {

  private int mScreeHeight;//屏幕高度
  private Scroller mScroller;
  private int mLastY;
  private int mStart;
  private int mEnd;
  private Context context;


  public MyScrollView(Context context) {
    super(context);
    initView(context);
  }

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

  public MyScrollView(Context context, AttributeSet attrs,
            int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    initView(context);
  }


  private void initView(Context context) {
    WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
    //DisplayMetrics 類(lèi)提供了一種關(guān)于顯示的通用信息，如顯示大小，分辨率和字體。
    DisplayMetrics dm = new DisplayMetrics();
    wm.getDefaultDisplay().getMetrics(dm);
    mScreeHeight = dm.heightPixels;//高度（像素）
    mScroller = new Scroller(context);
  }

  //繼承ViewGroup必須要實(shí)現(xiàn)的方法
  @Override
  protected void onLayout(boolean changed, int l, int t, int r, int b) {
    int childCount = getChildCount();//獲取子view的個(gè)數(shù)
    //設(shè)置ViewGroup的高度
    MarginLayoutParams mlp = (MarginLayoutParams) getLayoutParams();
    mlp.height = mScreeHeight * childCount;
    setLayoutParams(mlp);
    for (int i = 0; i < childCount; i++) {
      View child = getChildAt(i);
      if (child.getVisibility() != View.GONE) {
        //參數(shù)為相對(duì)父容器的左上右下位置,第三個(gè)參數(shù)必須為r
        child.layout(0, i * mScreeHeight, r, (i + 1) * mScreeHeight);
      }
    }
  }

  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    int count = getChildCount();
    for (int i = 0; i < count; i++) {
      View child = getChildAt(i);
      measureChild(child, widthMeasureSpec, heightMeasureSpec);
    }
  }

  @Override
  public boolean onTouchEvent(MotionEvent event) {
    int y = (int) event.getY();//相對(duì)于view的y值，getRawY()是相對(duì)屏幕
    switch (event.getAction()) {
      case MotionEvent.ACTION_DOWN:
        mLastY = y;//上一次的y值
        mStart = getScrollY();//記錄觸摸起點(diǎn)
        break;
      case MotionEvent.ACTION_MOVE:
        if(!mScroller.isFinished()) {
          mScroller.abortAnimation();//放棄移到最終位置
        }
        int dy = mLastY - y;//偏移距離
        //如果滑動(dòng)距離小于0或大于屏幕高度，不偏移
        if(getScrollY()<0){
          dy = 0;
        }
        if(getScrollY() > getHeight()-mScreeHeight){
          dy = 0;
        }
        scrollBy(0,dy);//移動(dòng)
        mLastY = y;
        break;
      case MotionEvent.ACTION_UP:
        int dScrollY = checkAlignment();//整體移動(dòng)的距離
        if(dScrollY > 0){
          if(dScrollY < mScreeHeight / 3){
            mScroller.startScroll(0,getScrollY(),0,-dScrollY);
          }else{
            mScroller.startScroll(0,getScrollY(),0,mScreeHeight-dScrollY);
          }
        }else{
          if(-dScrollY < mScreeHeight / 3){
            mScroller.startScroll(0,getScrollY(),0,-dScrollY);
          }else{
            mScroller.startScroll(0,getScrollY(),0,-mScreeHeight-dScrollY);
          }
        }
        break;
    }
    postInvalidate();
    return true;
  }

  private int checkAlignment(){
     mEnd = getScrollY();//記錄觸摸終點(diǎn)
    boolean isUp = ((mEnd - mStart)>0) ? true : false;
    int lastPrev = mEnd % mScreeHeight;
    int lastNext = mScreeHeight - lastPrev;
    if(isUp){
      return lastPrev;//向上
    }else
      return -lastNext;
  }

  @Override
  public void computeScroll() {
    super.computeScroll();
    if(mScroller.computeScrollOffset()){//返回true，表示還未移動(dòng)完
      scrollTo(0,mScroller.getCurrY());//移到當(dāng)前位置
      postInvalidate();
      //invalidate()是用來(lái)刷新View的，必須是在UI線(xiàn)程中進(jìn)行工作。
      //postInvalidate()可以在非UI線(xiàn)程調(diào)用
    }
  }
}

DisplayMetrics metric = new DisplayMetrics(); 
//API 17之后使用，獲取的像素寬高包含虛擬鍵所占空間，在API 17之前通過(guò)反射獲取 
context.getWindowManager().getDefaultDisplay().getRealMetrics(metric); 
//獲取的像素寬高不包含虛擬鍵所占空間 
//context.getWindowManager().getDefaultDisplay().getMetrics(metric); 
int width = metric.widthPixels; // 寬度（像素） 
int height = metric.heightPixels; // 高度（像素） 
float density = metric.density; // dp縮放因子 
int densityDpi = metric.densityDpi; // 廣義密度 
float xdpi = metric.xdpi;//x軸方向的真實(shí)密度 
float ydpi = metric.ydpi;//y軸方向的真實(shí)密度 

private int getStatusBarHeight() { 
  Rect rect = new Rect(); 
  getWindow().getDecorView().getWindowVisibleDisplayFrame(rect); 
  return rect.top; 
}