Android畫個時鐘玩玩

先看下最終的效果

開始實現
新建一個ClockView集成View

  public class ClockView extends View {

  }

先重寫onMeasure方法，這裡要先說一下View的測量模式，一共有三種：
1、EXACTLY

即精確值模式，當我們將控件的layout_width屬性或layout_height屬性指定為具體數值時，比如android:layout_width="100dp"，或者指定為math_parent屬性時（占據父View的大小），系統使用的是EXACTLY模式。

2、AT_MOST

即最大值模式，當控件的layout_width屬性或layout_height屬性指定為wrap_content時，控件大小一般隨著控件的子控件或內容的變化而變化，此時控件的尺寸只要不超過父控件允許的最大尺寸即可。

3、UNSPECIFIED

這個屬性比較奇怪——它不指定其大小測量模式，View想多大就多大，通常情況下在繪制自定義View時才會使用。

因為View的onMeasure方法只支持EXACTLY模式，當layout_width和layout_height為wrap_content時，View的大小就顯得很奇怪了，如下圖。

所以我們重寫一下onMeasure方法可以指定View width、height的最小值

  /**
   * 當布局為wrap_content時設置默認長寬
   * @param widthMeasureSpec
   * @param heightMeasureSpec
   */
  @Override
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    setMeasuredDimension(measure(widthMeasureSpec), measure(heightMeasureSpec));
  }

  private int measure(int origin){
    int result = DEFAULT_MIN_WIDTH;
    int specMode = MeasureSpec.getMode(origin);
    int specSize = MeasureSpec.getSize(origin);
    if(specMode == MeasureSpec.EXACTLY){
      result = specSize;
    }else{
      if(specMode == MeasureSpec.AT_MOST){
        result = Math.min(result, specSize);
      }
    }
    return result;
  }

下面就是最重要的重寫onDraw方法來繪制表盤、刻度、指針……，大致流程如下
1、畫表盤，用drawCircle繪制一個圓作為表盤, 圓心坐標為(getWidth()/2, getHeight()/2)，半徑為Math.min(getHeight()/2, getWidth()/2)。

//畫外圓
float borderWidth = DEFAULT_BORDER_WIDTH;
Paint paintCircle = new Paint();
paintCircle.setStyle(Paint.Style.STROKE);
paintCircle.setAntiAlias(true);
paintCircle.setStrokeWidth(borderWidth);
canvas.drawCircle(getWidth() / 2, getHeight() / 2, Math.min(getHeight() / 2, getWidth() / 2) - borderWidth / 2, paintCircle);

2、畫刻度線，在這裡我們可以利用一個`canvas.rotate'方法就可以不用計算角度了

//畫刻度線
float degreeLength = 0f;
Paint paintDegree = new Paint();
paintDegree.setAntiAlias(true);
for(int i=0;i<60;i++){
  if(i % 5 == 0){
    paintDegree.setStrokeWidth(6);
    degreeLength = DEFAULT_LONG_DEGREE_LENGTH;
  }else{
    paintDegree.setStrokeWidth(3);
    degreeLength = DEFAULT_SHORT_DEGREE_LENGTH;
  }
  canvas.drawLine(getWidth()/2, Math.abs(getWidth()/2 - getHeight()/2), getWidth()/2, Math.abs(getWidth()/2 - getHeight()/2) + degreeLength, paintDegree);
  canvas.rotate(360/60, getWidth()/2, getHeight()/2);
}

3、畫刻度上的數字

//刻度數字
int degressNumberSize = 30;
canvas.translate(getWidth() / 2, getHeight() / 2);
Paint paintDegreeNumber = new Paint();
paintDegreeNumber.setTextAlign(Paint.Align.CENTER);
paintDegreeNumber.setTextSize(degressNumberSize);
paintDegreeNumber.setFakeBoldText(true);
for(int i=0;i<12;i++){
  float[] temp = calculatePoint((i+1)*30, r - DEFAULT_LONG_DEGREE_LENGTH - degressNumberSize/2 - 15);
  canvas.drawText((i+1)+"", temp[2], temp[3] + degressNumberSize/2-6, paintDegreeNumber);
}

/**
 * 根據角度和長度計算線段的起點和終點的坐標
 * @param angle
 * @param length
 * @return
 */
private float[] calculatePoint(float angle, float length){
  float[] points = new float[4];
  if(angle <= 90f){
    points[0] = -(float) Math.sin(angle*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;
    points[1] = (float) Math.cos(angle*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;
    points[2] = (float) Math.sin(angle*Math.PI/180) * length;
    points[3] = -(float) Math.cos(angle*Math.PI/180) * length;
  }else if(angle <= 180f){
    points[0] = -(float) Math.cos((angle-90)*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;
    points[1] = -(float) Math.sin((angle-90)*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;
    points[2] = (float) Math.cos((angle-90)*Math.PI/180) * length;
    points[3] = (float) Math.sin((angle-90)*Math.PI/180) * length;
  }else if(angle <= 270f){
    points[0] = (float) Math.sin((angle-180)*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;
    points[1] = -(float) Math.cos((angle-180)*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;
    points[2] = -(float) Math.sin((angle-180)*Math.PI/180) * length;
    points[3] = (float) Math.cos((angle-180)*Math.PI/180) * length;
  }else if(angle <= 360f){
    points[0] = (float) Math.cos((angle-270)*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;
    points[1] = (float) Math.sin((angle-270)*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;
    points[2] = -(float) Math.cos((angle-270)*Math.PI/180) * length;
    points[3] = -(float) Math.sin((angle-270)*Math.PI/180) * length;
  }
  return points;
}

4、畫指針

//畫指針
Paint paintHour = new Paint();
paintHour.setAntiAlias(true);
paintHour.setStrokeWidth(15);
Paint paintMinute = new Paint();
paintMinute.setAntiAlias(true);
paintMinute.setStrokeWidth(10);
Paint paintSecond = new Paint();
paintSecond.setAntiAlias(true);
paintSecond.setStrokeWidth(5);
Calendar now = Calendar.getInstance();
float[] hourPoints = calculatePoint(now.get(Calendar.HOUR_OF_DAY)%12/12f*360, hourPointerLength);
canvas.drawLine(hourPoints[0], hourPoints[1], hourPoints[2], hourPoints[3], paintHour);
float[] minutePoints = calculatePoint(now.get(Calendar.MINUTE)/60f*360, minutePointerLength);
canvas.drawLine(minutePoints[0], minutePoints[1], minutePoints[2], minutePoints[3], paintMinute);
float[] secondPoints = calculatePoint(now.get(Calendar.SECOND)/60f*360, secondPointerLength);
canvas.drawLine(secondPoints[0], secondPoints[1], secondPoints[2], secondPoints[3], paintSecond);

5、畫圓心

//畫圓心
Paint paintCenter = new Paint();
paintCenter.setColor(Color.WHITE);
canvas.drawCircle(0, 0, 2, paintCenter);
最後只要啟動一個無限循環的線程，每隔1秒針重繪一下View就能讓指針動起來了
private Thread timeThread = new Thread() {
  @Override
  public void run() {
    try {
      while(true){
        updateHandler.sendEmptyMessage(0);
        Thread.sleep(1000);
      }
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }
};

private Handler updateHandler = new Handler() {
  @Override
  public void handleMessage(Message msg) {
    invalidate();
  }
};

以上就是教大家如何利用Android畫個時鐘的詳細步驟代碼，希望對大家的學習Android軟件編程有所幫助。