android自定义view写一个时间刻度尺

时间刻度尺是一个常见的自定义view，用于显示时间或者长度的刻度。下面是一个简单的时间刻度尺的实现代码：

public class TimeRulerView extends View {

    private int mWidth;
    private int mHeight;
    private int mPaddingLeft;
    private int mPaddingRight;
    private int mPaddingTop;
    private int mPaddingBottom;
    private int mTickWidth;
    private int mTickHeight;
    private int mTickGap;
    private int mTickColor;
    private int mLabelColor;
    private int mLabelTextSize;
    private int mMinValue;
    private int mMaxValue;
    private int mValue;
    private OnValueChangeListener mListener;

    public TimeRulerView(Context context) {
        this(context, null);
    }

    public TimeRulerView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public TimeRulerView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.TimeRulerView);
        mTickWidth = ta.getDimensionPixelSize(R.styleable.TimeRulerView_tickWidth, dp2px(1));
        mTickHeight = ta.getDimensionPixelSize(R.styleable.TimeRulerView_tickHeight, dp2px(10));
        mTickGap = ta.getDimensionPixelSize(R.styleable.TimeRulerView_tickGap, dp2px(10));
        mTickColor = ta.getColor(R.styleable.TimeRulerView_tickColor, Color.BLACK);
        mLabelColor = ta.getColor(R.styleable.TimeRulerView_labelColor, Color.BLACK);
        mLabelTextSize = ta.getDimensionPixelSize(R.styleable.TimeRulerView_labelTextSize, sp2px(12));
        mMinValue = ta.getInt(R.styleable.TimeRulerView_minValue, 0);
        mMaxValue = ta.getInt(R.styleable.TimeRulerView_maxValue, 24);
        mValue = ta.getInt(R.styleable.TimeRulerView_value, 0);
        ta.recycle();
    }

    public void setValue(int value) {
        if (value < mMinValue) {
            value = mMinValue;
        } else if (value > mMaxValue) {
            value = mMaxValue;
        }
        if (value != mValue) {
            mValue = value;
            invalidate();
            if (mListener != null) {
                mListener.onValueChange(mValue);
            }
        }
    }

    public void setOnValueChangeListener(OnValueChangeListener listener) {
        mListener = listener;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        mWidth = MeasureSpec.getSize(widthMeasureSpec);
        mHeight = MeasureSpec.getSize(heightMeasureSpec);
        mPaddingLeft = getPaddingLeft();
        mPaddingRight = getPaddingRight();
        mPaddingTop = getPaddingTop();
        mPaddingBottom = getPaddingBottom();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.save();
        canvas.translate(mPaddingLeft, mPaddingTop);
        drawTicks(canvas);
        drawLabels(canvas);
        canvas.restore();
    }

    private void drawTicks(Canvas canvas) {
        Paint paint = new Paint();
        paint.setColor(mTickColor);
        paint.setStrokeWidth(mTickWidth);
        for (int i = mMinValue; i <= mMaxValue; i++) {
            int x = i * mTickGap;
            int y1 = 0;
            int y2 = mTickHeight;
            canvas.drawLine(x, y1, x, y2, paint);
        }
    }

    private void drawLabels(Canvas canvas) {
        Paint paint = new Paint();
        paint.setColor(mLabelColor);
        paint.setTextSize(mLabelTextSize);
        paint.setTextAlign(Paint.Align.CENTER);
        Paint.FontMetrics fm = paint.getFontMetrics();
        int baseline = (int) ((mTickHeight + fm.bottom - fm.top) / 2 - fm.bottom);
        for (int i = mMinValue; i <= mMaxValue; i++) {
            int x = i * mTickGap;
            String text = String.valueOf(i);
            canvas.drawText(text, x, mTickHeight + baseline + dp2px(5), paint);
        }
    }

    private int dp2px(float dpValue) {
        float scale = getResources().getDisplayMetrics().density;
        return (int) (dpValue * scale + 0.5f);
    }

    private int sp2px(float spValue) {
        float scale = getResources().getDisplayMetrics().scaledDensity;
        return (int) (spValue * scale + 0.5f);
    }

    public interface OnValueChangeListener {
        void onValueChange(int value);
    }
}

上面的代码中，我们定义了一些自定义属性，如刻度线的宽度、高度、间距、颜色，标签的颜色、大小等。在onDraw方法中，我们先绘制刻度线，再绘制标签。在setValue方法中，我们检查输入值是否超出范围，并且通知监听器更新值。

在布局文件中，我们可以这样使用：

<com.example.timeruler.TimeRulerView
    android:id="@+id/time_ruler"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:tickWidth="1dp"
    app:tickHeight="10dp"
    app:tickGap="10dp"
    app:tickColor="#000000"
    app:labelColor="#000000"
    app:labelTextSize="12sp"
    app:minValue="0"
    app:maxValue="24"
    app:value="0"/>

最后，我们可以在Activity中设置监听器，获取时间刻度尺的值：

TimeRulerView timeRuler = findViewById(R.id.time_ruler);
timeRuler.setOnValueChangeListener(new TimeRulerView.OnValueChangeListener() {
    @Override
    public void onValueChange(int value) {
        Log.d("TimeRulerView", "Value changed: " + value);
    }
});

这样，我们就实现了一个简单的时间刻度尺。