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Android實現簡單時鐘View的方法

 更新時間：2022年05月17日 11:23:26   作者：swt369  
這篇文章主要為大家詳細介紹了Android實現簡單的時鐘View，關鍵點在Canvas的平移與旋轉，具有一定的參考價值，感興趣的小伙伴們可以參考一下

通過Canvas的平移與旋轉簡化繪圖邏輯是一個非常有用的技巧，下面的時鐘view就是利用這個方法完成的，省去了使用三角函數計算坐標的麻煩。

clock

package com.example.swt369.simpleclock;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewTreeObserver;
import android.widget.Toast;

import java.util.Calendar;

/**
 * Created by swt369 on 2017/8/20.
 */

public class ClockView extends View {
 //時鐘各個部件的長度
 private float mScaleLengthLong;
 private float mScaleLengthShort;
 private float mTickLengthHour;
 private float mTickLengthMinute;
 private float mTickLengthSecond;
 //view的寬和高
 private float mWidth;
 private float mHeight;
 //時鐘半徑
 private float mRadius;

 //繪制各部件時用的Paint
 private Paint mPaintScaleLong;
 private Paint mPaintScaleShort;
 private Paint mPaintOutline;
 private Paint mPaintNum;
 private Paint mPaintTickHour;
 private Paint mPaintTickMinute;
 private Paint mPaintTickSecond;

 private ViewTreeObserver.OnPreDrawListener onPreDrawListener;
 public ClockView(final Context context, @Nullable AttributeSet attrs) {
  super(context, attrs);

  onPreDrawListener = new ViewTreeObserver.OnPreDrawListener() {
   //獲取view寬高并計算各個部件的長度
   @Override
   public boolean onPreDraw() {
    mWidth = getMeasuredWidth();
    mHeight = getMeasuredHeight();
    mRadius = Math.min(mWidth,mHeight) / 2 * 0.95f;
    mScaleLengthLong = mRadius * 0.1f;
    mScaleLengthShort = mRadius * 0.05f;
    mTickLengthHour = mRadius * 0.3f;
    mTickLengthMinute = mRadius * 0.45f;
    mTickLengthSecond = mRadius * 0.6f;
    return true;
   }
  };
  getViewTreeObserver().addOnPreDrawListener(onPreDrawListener);

  //點擊顯示具體時間
  setOnClickListener(new OnClickListener() {
   @Override
   public void onClick(View v) {
    Calendar calendar = Calendar.getInstance();
    String time = String.format("當前時間：%02d:%02d:%02d",
      calendar.get(Calendar.HOUR_OF_DAY),calendar.get(Calendar.MINUTE),calendar.get(Calendar.SECOND));
    Toast.makeText(context,time, Toast.LENGTH_SHORT).show();
   }
  });

  //初始化所有Paint對象
  initializePaints();
 }

 @Override
 protected void onDraw(Canvas canvas) {
  if(mWidth == 0 || mHeight == 0){
   return;
  }
  if(onPreDrawListener != null){
   getViewTreeObserver().removeOnPreDrawListener(onPreDrawListener);
   onPreDrawListener = null;
  }
  //繪制時鐘
  drawClock(canvas);
  //一秒后重繪
  postInvalidateDelayed(1000);
 }

 private void drawClock(Canvas canvas) {
  //保存原始狀態(tài)
  canvas.save();

  //將坐標系原點移到中心，并逆時針旋轉90度。完成后x軸朝上。
  canvas.translate(mWidth / 2,mHeight / 2);
  canvas.rotate(-90);

  //畫外圍輪廓
  canvas.drawCircle(0,0,mRadius, mPaintOutline);

  //畫刻度
  for(int i = 0 ; i < 12 ; i++){
   String num = String.valueOf(i == 0 ? 12 : i);
   if(i % 3 == 0){
    canvas.drawLine(mRadius,0,mRadius - mScaleLengthLong,0, mPaintScaleLong);
   }else {
    canvas.drawLine(mRadius,0,mRadius - mScaleLengthShort,0, mPaintScaleShort);
   }
   canvas.drawText(num,mRadius - mScaleLengthLong - mPaintNum.measureText(num) * 2,0, mPaintNum);

   //順時針旋轉30度
   canvas.rotate(30);
  }

  Calendar calendar = Calendar.getInstance();

  //畫時針
  int hour = calendar.get(Calendar.HOUR);
  canvas.save();
  canvas.rotate(hour * 30);
  canvas.drawLine(0,0,mTickLengthHour,0,mPaintTickHour);
  canvas.restore();

  //畫分針
  int minute = calendar.get(Calendar.MINUTE);
  canvas.save();
  canvas.rotate(minute * 6);
  canvas.drawLine(0,0,mTickLengthMinute,0,mPaintTickMinute);
  canvas.restore();

  //畫秒針
  int second = calendar.get(Calendar.SECOND);
  canvas.save();
  canvas.rotate(second * 6);
  canvas.drawLine(0,0,mTickLengthSecond,0,mPaintTickSecond);
  canvas.restore();

  //恢復原始狀態(tài)
  canvas.restore();
 }

 private void initializePaints(){
  mPaintScaleLong = new Paint();
  mPaintScaleLong.setAntiAlias(true);
  mPaintScaleLong.setStrokeWidth(5);

  mPaintScaleShort = new Paint();
  mPaintScaleShort.setAntiAlias(true);
  mPaintScaleShort.setStrokeWidth(3);

  mPaintOutline = new Paint();
  mPaintOutline.setStyle(Paint.Style.STROKE);
  mPaintOutline.setAntiAlias(true);
  mPaintOutline.setStrokeWidth(5);

  mPaintNum = new Paint();
  mPaintNum.setTextSize(30);

  mPaintTickHour = new Paint();
  mPaintTickHour.setAntiAlias(true);
  mPaintTickHour.setStrokeWidth(6);

  mPaintTickMinute = new Paint();
  mPaintTickMinute.setAntiAlias(true);
  mPaintTickMinute.setStrokeWidth(4);

  mPaintTickSecond = new Paint();
  mPaintTickSecond.setAntiAlias(true);
  mPaintTickSecond.setStrokeWidth(2);
 }
}

代碼注釋已經比較詳細了，下面把比較重要的部分再說明一下：

//保存原始狀態(tài)
canvas.save();

//省略中間部分...

//恢復原始狀態(tài)
canvas.restore();

在繪圖開始時調用canvas.save()，可以保存下未經任何平移、旋轉操作的原始畫布狀態(tài)。在所有繪圖工作完成后調用canvas.restore()，可以恢復到上一次保存的狀態(tài)（類似進出棧的感覺）。

//將坐標系原點移到中心，并逆時針旋轉90度。完成后x軸朝上。
canvas.translate(mWidth / 2,mHeight / 2);
canvas.rotate(-90);

畫布的平移與旋轉可能比較抽象，可以想象成坐標系的平移與旋轉。調用canvas.translate(dx,dy)相當于將坐標原點向x,y方向移動了dx,dy的距離，調用canvas.rotate(degree)相當于坐標系順時針旋轉了degree°。

//畫刻度
for(int i = 0 ; i < 12 ; i++){
 String num = String.valueOf(i == 0 ? 12 : i);
 if(i % 3 == 0){
  canvas.drawLine(mRadius,0,mRadius - mScaleLengthLong,0, mPaintScaleLong);
 }else {
  canvas.drawLine(mRadius,0,mRadius - mScaleLengthShort,0, mPaintScaleShort);
 }
 canvas.drawText(num,mRadius - mScaleLengthLong - mPaintNum.measureText(num) * 2,0, mPaintNum);

 //順時針旋轉30度
 canvas.rotate(30);
}

根據i值決定是畫大刻度（90°的倍數）還是小刻度。每次畫完一條之后將坐標系順時針旋轉30°，這樣保證每次畫的刻度線的坐標不變。

//一秒后重繪
postInvalidateDelayed(1000);

作用是在1000ms（1s）后再次執(zhí)行View的draw流程，產生指針運動的效果。

以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持腳本之家。

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