Android 自定义TextView，水平滚动

package com.my.androidtext.view;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.os.Parcel;
import android.os.Parcelable;
import android.text.TextPaint;
import android.util.AttributeSet;
import android.view.View;

import androidx.appcompat.widget.AppCompatTextView;


public class HorizontalTextView extends AppCompatTextView {
    private float textLength = 0f;
    private float viewWidth = 0f;
    private float viewHeight = 0f;
    private float step = 0f;
    private float y = 0f;
    public boolean isStarting = false;
    private Paint paint = null;
    private Paint mBitPaint = null;
    private Bitmap mBitmap;
    private String text = "";
    private boolean isInit = false;
    private boolean isCanScroll = true;
    private static final String POINT = "...";
    private boolean textMarginRight = false;

    public HorizontalTextView(Context context) {
        super(context);
        initTextView();
    }

    public HorizontalTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initTextView();
    }

    public HorizontalTextView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        initTextView();
    }


    @Override
    public Parcelable onSaveInstanceState() {
        Parcelable superState = super.onSaveInstanceState();
        SavedState ss = new SavedState(superState);

        ss.step = step;
        ss.isStarting = isStarting;

        return ss;
    }

    @Override
    public void onRestoreInstanceState(Parcelable state) {
        if (!(state instanceof SavedState)) {
            super.onRestoreInstanceState(state);
            return;
        }
        SavedState ss = (SavedState) state;
        super.onRestoreInstanceState(ss.getSuperState());

        step = ss.step;
        isStarting = ss.isStarting;

    }

    public static class SavedState extends View.BaseSavedState {
        public boolean isStarting = false;
        public float step = 0.0f;

        SavedState(Parcelable superState) {
            super(superState);
        }

        @Override
        public void writeToParcel(Parcel out, int flags) {
            super.writeToParcel(out, flags);
            out.writeBooleanArray(new boolean[]{isStarting});
            out.writeFloat(step);
        }


        public static final Creator<SavedState> CREATOR
                = new Creator<SavedState>() {

            public SavedState[] newArray(int size) {
                return new SavedState[size];
            }

            @Override
            public SavedState createFromParcel(Parcel in) {
                return new SavedState(in);
            }
        };

        private SavedState(Parcel in) {
            super(in);
            try {
                boolean[] b = null;
                in.readBooleanArray(b);
                if (b != null && b.length > 0)
                    isStarting = b[0];
                step = in.readFloat();
            } catch (Exception e) {

            }
        }
    }

    public void setCanScroll(boolean canScroll) {
        isCanScroll = canScroll;
    }

    public void setTextMarginRight(boolean textMarginRight) {
        this.textMarginRight = textMarginRight;
    }

    private void startScroll() {
        isStarting = true;
        invalidate();
    }


    private void stopScroll() {
        isStarting = false;
        invalidate();
    }

    @Override
    public void onDraw(Canvas canvas) {
        if (!isInit) {
            initTextView();
        }
        canvas.drawText(text, step, y, paint);

        if (!isStarting) {
            return;
        }
        step -= 1;
        if (-step > textLength)
            step = viewWidth;
        invalidate();
    }


    @Override
    protected void onTextChanged(CharSequence text, int start, int lengthBefore, int lengthAfter) {
        super.onTextChanged(text, start, lengthBefore, lengthAfter);
        isInit = false;
    }

    private void initTextView() {
        paint = this.getPaint();
        paint.setColor(getCurrentTextColor());
        paint.setTextSize(getTextSize());

        text = this.getText().toString().trim();
        textLength = paint.measureText(text);

        step = 0;

        Paint.FontMetrics fontMetrics = paint.getFontMetrics();
        ///文字一半的高度再减去基线到bottom的高度，
        float halfHeight = (fontMetrics.bottom - fontMetrics.top) / 2 - fontMetrics.bottom;
        y = getHeight() / 2 + (int) halfHeight;

        if (textLength > viewWidth) {
            if (isCanScroll) {
                startScroll();
            } else {
                reInitTextWithPoint();
                stopScroll();
            }
        } else {
            if (textMarginRight) {
                step = viewWidth - textLength;
            }
            stopScroll();
        }
        isInit = true;
    }

    private void reInitTextWithPoint() {
        TextPaint textPaint = new TextPaint();
        textPaint.setTextSize(this.getTextSize());
        while (textPaint.measureText(text) >= (viewWidth - textPaint.measureText(POINT))) {
            text = text.substring(0, text.length() - 1);
        }
        text += POINT;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        viewWidth = View.MeasureSpec.getSize(widthMeasureSpec);
        viewHeight = View.MeasureSpec.getSize(heightMeasureSpec);
        setMeasuredDimension((int) viewWidth, (int) viewHeight);
    }
}