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Android實(shí)現(xiàn)簡單時(shí)鐘View的方法

 更新時(shí)間：2022年05月17日 11:23:26   作者：swt369  
這篇文章主要為大家詳細(xì)介紹了Android實(shí)現(xiàn)簡單的時(shí)鐘View，關(guān)鍵點(diǎn)在Canvas的平移與旋轉(zhuǎn)，具有一定的參考價(jià)值，感興趣的小伙伴們可以參考一下

通過Canvas的平移與旋轉(zhuǎn)簡化繪圖邏輯是一個(gè)非常有用的技巧，下面的時(shí)鐘view就是利用這個(gè)方法完成的，省去了使用三角函數(shù)計(jì)算坐標(biāo)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(shí)鐘各個(gè)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(shí)鐘半徑
 private float mRadius;

 //繪制各部件時(shí)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(jì)算各個(gè)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(diǎn)擊顯示具體時(shí)間
  setOnClickListener(new OnClickListener() {
   @Override
   public void onClick(View v) {
    Calendar calendar = Calendar.getInstance();
    String time = String.format("當(dāng)前時(shí)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(duì)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(shí)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(biāo)系原點(diǎn)移到中心，并逆時(shí)針旋轉(zhuǎn)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(shí)針旋轉(zhuǎn)30度
   canvas.rotate(30);
  }

  Calendar calendar = Calendar.getInstance();

  //畫時(shí)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(fù)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(jīng)比較詳細(xì)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(fù)原始狀態(tài)
canvas.restore();

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

//將坐標(biāo)系原點(diǎn)移到中心，并逆時(shí)針旋轉(zhuǎn)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(zhuǎn)可能比較抽象，可以想象成坐標(biāo)系的平移與旋轉(zhuǎn)。調(diào)用canvas.translate(dx,dy)相當(dāng)于將坐標(biāo)原點(diǎn)向x,y方向移動(dòng)了dx,dy的距離，調(diào)用canvas.rotate(degree)相當(dāng)于坐標(biāo)系順時(shí)針旋轉(zhuǎn)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(shí)針旋轉(zhuǎn)30度
 canvas.rotate(30);
}

根據(jù)i值決定是畫大刻度（90°的倍數(shù)）還是小刻度。每次畫完一條之后將坐標(biāo)系順時(shí)針旋轉(zhuǎn)30°，這樣保證每次畫的刻度線的坐標(biāo)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(chǎn)生指針運(yùn)動(dòng)的效果。

以上就是本文的全部內(nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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