Android 自定义View 实例实例AnalogClock 源码源码
针对Android 底层View 的直接构造很多网友没有实战经验，本次Android 开发网结合目前平台开源代码一起通过
AnalogClock 类来理解View 的直接继承。AnalogClock 就是Home Screen 上的那个带有两根指针的表盘类。它的实现我们直
接从开源代码可以了解到:
public class AnalogClock extends View {
private Time mCalendar;
private Drawable mHourHand; //时针
private Drawable mMinuteHand; //分针
private Drawable mDial; //表盘背景
private int mDialWidth; //表盘宽度
private int mDialHeight; //表盘高度
private boolean mAttached; //附着状态
private final Handler mHandler = new Handler(); //定一个Handler 类实现更新时间
private float mMinutes;
private float mHour;
private boolean mChanged; //时间是否改变
public AnalogClock(Context context) {
this(context, null);
}
public AnalogClock(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public AnalogClock(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
Resources r = mContext.getResources();
TypedArray a = context.obtainStyledAttributes(
attrs, com.android.internal.R.styleable.AnalogClock, defStyle, 0);
mDial = a.getDrawable(com.android.internal.R.styleable.AnalogClock_dial); //加载表盘资源
if (mDial == null) {
mDial = r.getDrawable(com.android.internal.R.drawable.clock_dial);
}
mHourHand = a.getDrawable(com.android.internal.R.styleable.AnalogClock_hand_hour); //加载时针图片资
源
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); //加载分针图
片
if (mMinuteHand == null) {
mMinuteHand = r.getDrawable(com.android.internal.R.drawable.clock_hand_minute);
} mCalendar = new Time(); //获取当前系统时间
mDialWidth = mDial.getIntrinsicWidth(); //获取表盘图片的宽度
mDialHeight = mDial.getIntrinsicHeight(); //高度，同上
}
@Override
protected void onAttachedToWindow() {
super.onAttachedToWindow();
if (!mAttached) {
mAttached = true;
IntentFilter filter = new IntentFilter();//注册一个消息过滤器,获取时间改变时区,改变action filter.addAction(Intent.ACTION_TIME_TICK);
filter.addAction(Intent.ACTION_TIME_CHANGED) ;
filter.addAction(Intent.ACTION_TIMEZONE_CHANGED);
getContext().registerReceiver(mIntentReceiver, filter, null, mHandler);
}
mCalendar = new Time();
onTimeChanged();
}
@Override
protected void onDetachedFromWindow() {
super.onDetachedFromWindow();
if (mAttached) {
getContext().unregisterReceiver(mIntentReceiver); //反注册消息过滤器
mAttached = false;
}
} @Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
int widthMode = MeasureSpec.getMode(widthMeasureSpec);
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
int heightMode = MeasureSpec.getMode(heightMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
float hScale = 1.0f;
float vScale = 1.0f;
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);
setMeasuredDimension(resolveSize((int) (mDialWidth * scale), widthMeasureSpec), resolveSize((int) (mDialHeight * scale), heightMeasureSpec));
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
mChanged = true;
} //主要的绘图重写View 的onDraw 方法，我们可以看到通过canvas 实例直接屏幕
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
boolean changed = mChanged;
if (changed) {
mChanged = false;
}
int availableWidth = mRight - mLeft; int availableHeight = mBottom - mTop; int x = availableWidth / 2