public class TrendGraph extends View {
  public TrendGraph(Context context) { // 在java代码中创建调用
    super(context);
  }

  public TrendGraph(Context context, AttributeSet attrs) { // 在xml中创建调用
    super(context, attrs);
  }
} 

   @Override
   protected void onDraw(Canvas canvas) {
     super.onDraw(canvas);
     if (mElements == null || mElements.size() == 0) {
       return;
     }
     double max_up = getMaxUp();
     double min_down = getMinDown();
     canvas.setDrawFilter(mDrawFilter);
     mPaint.setStrokeWidth(lineWeith);
     float width = getWidth();
     float grap = width / mElements.size();
     float textSize = mTextPaint.getTextSize();
     int textMargin = circleRadius * 2;
     float margin_top = textSize + 2 * textMargin;
     Log.d(TAG, "onDraw: " + margin_top + "|" + textSize);
     float height = getHeight() - 2 * margin_top;
 
     for (int i = 0; i < mElements.size() - 1; i++) {
       float startX = i * grap + grap / 2;
       float stopX = (i + 1) * grap + grap / 2;
       float startY = (float) (max_up - mElements.get(i).getUp()) / (float) (max_up -
           min_down) * height + margin_top;
       float stopY = (float) (max_up - mElements.get(i + 1).getUp()) / (float) (max_up -
           min_down) * height + margin_top;
 
       canvas.drawText((int) mElements.get(i).getUp() + "℃", startX - textSize, startY -
           textMargin, mTextPaint);
       canvas.drawCircle(startX, startY, circleRadius, mPaint);
       canvas.drawLine(startX, startY, stopX, stopY, mPaint);
       if (i == mElements.size() - 2) {
         canvas.drawText((int) mElements.get(i + 1).getUp() + "℃", stopX - textSize, stopY
             - textMargin, mTextPaint);
         canvas.drawCircle(stopX, stopY, circleRadius, mPaint);
       }
 
       startY = (float) (max_up - mElements.get(i).getDown()) / (float) (max_up - min_down) *
           height + margin_top;
       stopY = (float) (max_up - mElements.get(i + 1).getDown()) / (float) (max_up -
           min_down) * height + margin_top;
       canvas.drawText((int) mElements.get(i).getDown() + "℃", startX - textSize, startY +
           textSize + textMargin, mTextPaint);
       canvas.drawCircle(startX, startY, circleRadius, mPaint);
       canvas.drawLine(startX, startY, stopX, stopY, mPaint);
       if (i == mElements.size() - 2) {
         canvas.drawText((int) mElements.get(i + 1).getDown() + "℃", stopX - textSize,
             stopY + textSize + textMargin, mTextPaint);
         canvas.drawCircle(stopX, stopY, circleRadius, mPaint);
       }
     }
   }

<?xml version="1.0" encoding="utf-8"?>
<resources>
  <declare-styleable name="TrendGraph">
    <attr name="lineWidth" format="dimension"/>
    <attr name="circleRadius" format="dimension" />
    <attr name="textSize" format="dimension" />
    <attr name="textColor" format="reference" />
  </declare-styleable>
</resources>

  public TrendGraph(Context context, AttributeSet attrs) {
    super(context, attrs);
    TypedArray array = getContext().obtainStyledAttributes(attrs, R.styleable.TrendGraph);
    circleRadius = array.getDimensionPixelSize(R.styleable.TrendGraph_circleRadius, 5);
    lineWeith = array.getDimensionPixelSize(R.styleable.TrendGraph_lineWidth, 3);
    mTextPaint.setTextSize(array.getDimensionPixelSize(R.styleable.TrendGraph_textSize, 35));
    mTextPaint.setColor(array.getColor(R.styleable.TrendGraph_textColor, Color.BLACK));
    array.recycle();
  }

xmlns:app=[url=http://schemas.android.com/apk/res-auto]http://schemas.android.com/apk/res-auto[/url]

  <com.fndroid.byweather.views.TrendGraph
    android:id="@+id/tg"
    android:layout_width="match_parent"
    app:textColor="@color/colorAccent"
    app:textSize="22sp"
    app:circleRadius="2dp"
    android:layout_height="200dp"/>

  public interface onItemClickListener{
    void onItemClick(View view, Element element);
  }

public class TrendGraph extends View {

  private onItemClickListener mOnItemClickListener;

  // 省略代码

  public void setOnItemClickListener(onItemClickListener onItemClickListener) {
    mOnItemClickListener = onItemClickListener;
  }

} 

  @Override
  public boolean onTouchEvent(MotionEvent event) {
    int viewWidth = getWidth();
    int itemWidth = viewWidth / mElements.size();
    int viewHeight = getHeight();
    boolean isMove = false; // 界面中最外层为一个NestedScrollView，所以为了避免滑动时也触发，加入变量处理

    switch (event.getAction()) {
      case MotionEvent.ACTION_MOVE:
        isMove = true;
        break;
      case MotionEvent.ACTION_UP:
        if (!isMove){ // 判断只有点击时进行回调
          int position = (int) (event.getX() / itemWidth); // 取得点击的位置
          mOnItemClickListener.onItemClick(this, mElements.get(position)); // 回调
        }
        break;
    }

    return true;
  }

　　historyGraph.setOnItemClickListener(this);
  @Override
  public void onItemClick(View view, TrendGraph.Element element) {
    int dt = (int) (element.getUp() - element.getDown());
    Snackbar.make(root, "当天温差为：" + dt + "℃", Snackbar.LENGTH_SHORT).show();
  }