Android 自定义 View 实例 AnalogClock

import android.content.Context;

import android.content.Intent;

import android.content.IntentFilter;

import android.content.BroadcastReceiver;

import android.content.res.Resources;

import android.content.res.TypedArray;

import android.graphics.Canvas;

import android.graphics.drawable.Drawable;

import android.os.Handler;

import android.text.format.DateUtils;

import android.text.format.Time;

import android.util.AttributeSet;

import android.view.View;

import android.widget.RemoteViews.RemoteView;

import java.util.TimeZone;

/**

* This widget display an analogic clock with two hands for hours and

* minutes.

*

* @attr ref android.R.styleable#AnalogClock_dial

* @attr ref android.R.styleable#AnalogClock_hand_hour

* @attr ref android.R.styleable#AnalogClock_hand_minute

*/

@RemoteView

public class AnalogClock extends View {

private Time mCalendar;

private Drawable mHourHand;//定义时针

private Drawable mMinuteHand;//定义分针

private Drawable mDial;//定义表盘

private int mDialWidth;//定义表盘的宽度

private int mDialHeight;//定义表盘的高度

private boolean mAttached;//定义是否是附着的view

private final Handler mHandler = new Handler();//handeler用来发送和处理消息，这里用来更新时间

private float mMinutes;//存储分钟的时间变量

private float mHour;//存储小时的时间变量

private boolean mChanged;//表示时间是否发生改变

//构造方法

public AnalogClock(Context context) {

this(context, null);

}

//构造方法

public AnalogClock(Context context, AttributeSet attrs) {

this(context, attrs, 0);

}

//构造方法

public AnalogClock(Context context, AttributeSet attrs,

int defStyle) {

super(context, attrs, defStyle);

Resources r = mContext.getResources();//获得当前Context中/res目录下的资源

//定义一个数组，用来存放

obtainStyledAttributes(AttributeSet,
int[], int, int)获得的类型值

TypedArray a =

context.obtainStyledAttributes(

attrs, com.android.internal.R.styleable.AnalogClock, defStyle, 0);

//相当于Resource.getDrawble,从styleable中获得dial的图片资源

mDial = a.getDrawable(com.android.internal.R.styleable.AnalogClock_dial);

if (mDial == null) {//如果找不到图片资源，则从/res/drawble下面寻找图片资源，下同

mDial = r.getDrawable(com.android.internal.R.drawable.clock_dial);

}

mHourHand = a.getDrawable(com.android.internal.R.styleable.AnalogClock_hand_hour);

if (mHourHand == null) {

mHourHand = r.getDrawable(com.android.internal.R.drawable.clock_hand_hour);

}

mMinuteHand = a.getDrawable(com.android.internal.R.styleable.AnalogClock_hand_minute);

if (mMinuteHand == null) {

mMinuteHand = r.getDrawable(com.android.internal.R.drawable.clock_hand_minute);

}

mCalendar = new Time();//初始化，获得当前的时间

mDialWidth = mDial.getIntrinsicWidth();//获得mDial的原始宽度

mDialHeight = mDial.getIntrinsicHeight();//获得mDial的原始高度

}

@Override

protected void onAttachedToWindow() {

super.onAttachedToWindow();

if (!mAttached) {//如果没有附着view

mAttached = true;

//声明意图（消息）过滤器,过滤类型为action，获得表针，时间，时区改变的信息

IntentFilter filter = new IntentFilter();

filter.addAction(Intent.ACTION_TIME_TICK);//添加一个表针移动的action

filter.addAction(Intent.ACTION_TIME_CHANGED);//添加一个时间改变的action

filter.addAction(Intent.ACTION_TIMEZONE_CHANGED);//添加一个时区改变action

//注册mIntentReceiver，接受filter信息

getContext().registerReceiver(mIntentReceiver, filter, null, mHandler);

}

// NOTE: It's safe to do these after registering the receiver since the receiver always runs

// in the main thread, therefore the receiver can't run before this method returns.

// The time zone may have changed while the receiver wasn't registered, so update the Time

mCalendar = new Time();//当receiver未注册时，时区可能已经改变，所以要更新当前时间

// Make sure we update to the current time

onTimeChanged();

}

@Override

protected void onDetachedFromWindow() {

super.onDetachedFromWindow();

if (mAttached) {//如果有附着窗口

getContext().unregisterReceiver(mIntentReceiver);//移除前面注册的mIntentReceiver

mAttached = false;

}

}

@Override

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

int widthMode = MeasureSpec.getMode(widthMeasureSpec);//获得MeasureSpec（测量规范）中的width的模式

int widthSize = MeasureSpec.getSize(widthMeasureSpec);//获得MeasureSpec（测量规范）中的width大小

int heightMode = MeasureSpec.getMode(heightMeasureSpec);

int heightSize = MeasureSpec.getSize(heightMeasureSpec);

float hScale = 1.0f;//水平的放缩规模

float vScale = 1.0f;//垂直方向的放缩规模

//如果widthMode不是指定的模式，并且widthSize < mDialWidth，则需要将view放缩，即扩大view尺寸

if (widthMode != MeasureSpec.UNSPECIFIED && widthSize < mDialWidth) {

hScale = (float) widthSize / (float) mDialWidth;

}

if (heightMode != MeasureSpec.UNSPECIFIED && heightSize < mDialHeight) {

vScale = (float )heightSize / (float) mDialHeight;

}

float scale = Math.min(hScale, vScale);//选择最小的放缩规模

//测量图片的高度和宽度，并存储之

setMeasuredDimension(resolveSizeAndState((int) (mDialWidth * scale), widthMeasureSpec, 0),

resolveSizeAndState((int) (mDialHeight * scale), heightMeasureSpec, 0));

}

@Override

protected void onSizeChanged(int w, int h, int oldw, int oldh) {

super.onSizeChanged(w, h, oldw, oldh);

mChanged = true;

}

@Override

protected void onDraw(Canvas canvas) {

super.onDraw(canvas);

boolean changed = mChanged;

if (changed) {

mChanged = false;

}

int availableWidth = mRight - mLeft;//availableWidth是整个屏幕的宽度，mRight是最右边的端点值，mLeft是最右边的端点值

int availableHeight = mBottom - mTop;//avaailableHeight是整个屏幕的高度，mBottom是屏幕最低端的端点值，mTop是最上端端点值

//(x,y)是屏幕的中心点的坐标

int x = availableWidth / 2;

int y = availableHeight / 2;

final Drawable dial = mDial;

int w = dial.getIntrinsicWidth();//获得dial的宽度

int h = dial.getIntrinsicHeight();//获得dial的高度

boolean scaled = false;

if (availableWidth < w || availableHeight < h) {//如果dial的宽度和高度大于屏幕的高度和宽度，就要进行重新绘制

scaled = true;

float scale = Math.min((float) availableWidth / (float) w,

(float) availableHeight / (float) h);//获得超出屏幕大小的比例

canvas.save();

canvas.scale(scale, scale, x, y);//扩大

}

if (changed) {//设置dial的边界，将dail放在view的正中间

dial.setBounds(x - (w / 2), y - (h / 2), x + (w / 2), y + (h / 2));

}

dial.draw(canvas);//在canvas上画出dial

canvas.save();//dial画完之后保存

canvas.rotate(mHour / 12.0f * 360.0f, x, y);//让时针绕点（x,y）旋转起来，mHour / 12.0f * 360.0f是时针旋转的角度

final Drawable hourHand = mHourHand;

if (changed) {

w = hourHand.getIntrinsicWidth();//获得时针图片的宽度

h = hourHand.getIntrinsicHeight();//获得时针图片的高度，下同

hourHand.setBounds(x - (w / 2), y - (h / 2), x + (w / 2), y + (h / 2));//设置时针的边界，将时针也放置在view的中间

}

hourHand.draw(canvas);//绘制时针

canvas.restore();//remove all modifications to the matrix/clip state since the last save call（取消上一次的保存）

canvas.save();//重新保存

canvas.rotate(mMinutes / 60.0f * 360.0f, x, y);//让分针绕点(x,y)旋转，mMinutes / 60.0f * 360.0f是分针的旋转角度

final Drawable minuteHand = mMinuteHand;

if (changed) {

w = minuteHand.getIntrinsicWidth();//获得分针的宽度

h = minuteHand.getIntrinsicHeight();//获得分针的高度

minuteHand.setBounds(x - (w / 2), y - (h / 2), x + (w / 2), y + (h / 2));//设置分针的边界，将其放在view的中间位置,即dial图片的中心在点(x,y)位置

}

minuteHand.draw(canvas);

canvas.restore();

if (scaled) {

canvas.restore();

}

}

private void onTimeChanged() {

mCalendar.setToNow();//获得当前的时间

int hour = mCalendar.hour;//获得当前时间的小时

int minute = mCalendar.minute;//获得当前时间的分钟

int second = mCalendar.second;//获得当前时间的秒

mMinutes = minute + second / 60.0f;//动态的显示没经过一秒钟时，mMinutes的值

mHour = hour + mMinutes / 60.0f;

mChanged = true;

updateContentDescription(mCalendar);

}

private final BroadcastReceiver mIntentReceiver = new BroadcastReceiver() {

@Override

public void onReceive(Context context, Intent intent) {

if (intent.getAction().equals(Intent.ACTION_TIMEZONE_CHANGED)) {//如果时区发生改变，就要更新时区

String tz = intent.getStringExtra("time-zone");

mCalendar = new Time(TimeZone.getTimeZone(tz).getID());

}

onTimeChanged();

invalidate();//使整个窗口客户区无效，Invalidate()之后：...OnPaint()->OnPrepareDC()->OnDraw()

}

};

private void updateContentDescription(Time time) {

final int flags = DateUtils.FORMAT_SHOW_TIME | DateUtils.FORMAT_24HOUR;

String contentDescription = DateUtils.formatDateTime(mContext,//按照当地习俗转换日期或时间格式（MM:SS或HH:MM:SS）

time.toMillis(false), flags);

setContentDescription(contentDescription);

}

}