目录

• 正文
• AutoLineChart完整代码

正文

一条折线，根据最大最小值自动缩放上下限。

• 继承View
• 数据使用FloatBuffer存储
• 可改变显示窗口的大小
• 可指定坐标轴，折线和字体颜色

AutoLineChart完整代码

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.util.Log;
import android.util.TypedValue;
import android.view.View;
import java.nio.FloatBuffer;
public class AutoLineChart extends View {
    private static final String TAG = "rustApp" + AutoLineChart.class.getSimpleName();
    private float yMax = 1.6f;
    private float yMin = -1.0f;
    float yAxisZoomLimitMax = 1.6f;
    float yAxisZoomLimitMin = -1.0f; // 缩小y轴的极限值
    // Y轴自动缩放时的增减距离
    float axisYPerStep = 0.1f;
    // 图表线条在view顶部留出的间距
    float viewYStart = 2;
    float axisTextSize = 10;
    private int onShowPointsCount = 500;  // 当前显示的数据个数
    int onShowMinPoints = 100;            // 至少要显示的数据个数
    private int maxPoint = 9000;          // 数据存储最大个数
    // 坐标轴线条宽度
    float axisLineWid = 1f;
    int dataLineWid = 4;
    // 数据线颜色
    private int dataColor = Color.parseColor("#eaffe9");
    // 图表中的背景线条颜色
    private int mainBgLineColor = Color.parseColor("#535353");
    // 坐标轴颜色
    private int axisColor = Color.WHITE;
    // 坐标值字体颜色
    private int axisTextColor = Color.WHITE;
    // 背景色
    private int viewBgColor = Color.parseColor("#222222");
    Rect rectText = new Rect();
    private float xStep = 1.0f;
    private float viewWidth;
    private float viewHeight;
    private float botLeftXOnView = 0; // 图表左下点在view中的x坐标
    private float botLeftYOnView = 0;
    private float originYToBottom = 20; // 图表原点距离view底部的距离
    private FloatBuffer dataBuffer;
    private Paint bgPaint;
    private Paint linePaint;
    public AutoLineChart(Context context) {
        this(context, null);
    }
    public AutoLineChart(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }
    public AutoLineChart(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context);
    }
    public int getMaxPoint() {
        return maxPoint;
    }
    public void setOnShowPointsCount(int onShowPointsCount) {
        this.onShowPointsCount = onShowPointsCount;
    }
    public int getOnShowPointsCount() {
        return onShowPointsCount;
    }
    public int getOnShowMinPoints() {
        return onShowMinPoints;
    }
    public void addData(float data) {
        dataBuffer.put(data);
        if (dataBuffer.position() > (dataBuffer.capacity() * 2 / 3)) {
            float[] bufferArr = dataBuffer.array();
            System.arraycopy(bufferArr, dataBuffer.position() - maxPoint, bufferArr, 0, maxPoint);
            dataBuffer.position(maxPoint);
//            Log.d(TAG, "把当前数据移动到buffer起始位置 " + dataBuffer);
        }
        invalidate();
    }
    private void init(Context context) {
        dataBuffer = FloatBuffer.allocate(3 * maxPoint); // 分配3倍的空间
        bgPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        linePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        bgPaint.setStrokeWidth(axisLineWid);
        bgPaint.setStyle(Paint.Style.STROKE);
        bgPaint.setColor(mainBgLineColor);
        linePaint.setStrokeWidth(dataLineWid);
        linePaint.setStyle(Paint.Style.STROKE);
        linePaint.setColor(dataColor);
        botLeftXOnView = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 32, context.getResources().getDisplayMetrics());
        originYToBottom = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 20, context.getResources().getDisplayMetrics());
        viewYStart = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 20, context.getResources().getDisplayMetrics());
        axisLineWid = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 1, context.getResources().getDisplayMetrics());
        axisTextSize = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, 10, context.getResources().getDisplayMetrics());
    }
    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        viewWidth = getWidth();
        viewHeight = getHeight();
        botLeftYOnView = viewHeight - originYToBottom;
    }
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawColor(viewBgColor);
        xStep = (viewWidth - botLeftXOnView) / (onShowPointsCount - 1);
        float maxData = 0.1f;
        float minData = 0;
        int dataStartIndexInBuffer = 0; // 数据在buffer中的起始下标
        if (dataBuffer.position() > onShowPointsCount) {
            dataStartIndexInBuffer = dataBuffer.position() - onShowPointsCount;
        }
        float[] bufferArr = dataBuffer.array();
        for (int i = dataStartIndexInBuffer; i < dataBuffer.position(); i++) {
            if (bufferArr[i] < minData) {
                minData = bufferArr[i];
            } else if (bufferArr[i] > maxData) {
                maxData = bufferArr[i];
            }
        }
        zoomYAxis(maxData, minData);
        drawBgLines(canvas);
        drawWave(canvas, dataStartIndexInBuffer);
    }
    // 缩放Y轴
    private void zoomYAxis(float maxData, float minData) {
        if (maxData < yAxisZoomLimitMax) {
            yMax = yAxisZoomLimitMax;
        } else if (maxData < yMax) {
            while (maxData < yMax) {
                yMax -= axisYPerStep;
            }
            yMax += axisYPerStep;
        } else if (maxData > yMax) {
            while (maxData > yMax) {
                yMax += axisYPerStep;
            }
        }
        if (minData > yAxisZoomLimitMin) {
            yMin = yAxisZoomLimitMin;
        } else if (minData > yMin) {
            while (minData > yMin) {
                yMin += axisYPerStep;
            }
            yMin -= axisYPerStep;
        } else if (minData < yMin) {
            yMin -= axisYPerStep;
        }
    }
    private void drawBgLines(Canvas canvas) {
        // 画坐标轴
        bgPaint.setStyle(Paint.Style.FILL);
        bgPaint.setStrokeWidth(axisLineWid);
        bgPaint.setTextSize(axisTextSize);
        bgPaint.setTextAlign(Paint.Align.RIGHT);
        for (float y = 0; y <= yMax; y += 0.5) {
            drawYAxis(canvas, y);
        }
        for (float y = 0; y >= yMin; y -= 0.5) {
            drawYAxis(canvas, y);
        }
        bgPaint.setColor(axisColor);
        canvas.drawLine(botLeftXOnView, viewYStart / 2, botLeftXOnView, botLeftYOnView + viewYStart / 2, bgPaint);
//        canvas.drawLine(botLeftXOnView, botLeftYOnView, viewWidth, botLeftYOnView, bgPaint); // x轴
    }
    private void drawYAxis(Canvas canvas, float axisYValue) {
        final float yDataRange = yMax - yMin;
        final float yAxisRangeOnView = botLeftYOnView - viewYStart;
        float aY = botLeftYOnView - (axisYValue - yMin) / yDataRange * yAxisRangeOnView;
        bgPaint.setColor(axisColor);
        canvas.drawLine(botLeftXOnView - 20, aY, botLeftXOnView, aY, bgPaint);
        String axisText = String.valueOf(axisYValue);
        bgPaint.getTextBounds(axisText, 0, axisText.length(), rectText); // 获取文本的宽高
        canvas.drawText(axisText, botLeftXOnView - rectText.width() / 2, aY + rectText.height() / 2, bgPaint);
        bgPaint.setColor(mainBgLineColor);
        canvas.drawLine(botLeftXOnView, aY, viewWidth, aY, bgPaint);
    }
    private void drawWave(Canvas canvas, int dataStartIndexInBuffer) {
        final float yDataRange = yMax - yMin;
        final float yAxisRangeOnView = botLeftYOnView - viewYStart;
        final float yDataStep = yAxisRangeOnView / yDataRange;
        float[] dataArr = dataBuffer.array();
        for (int i = dataStartIndexInBuffer; i < dataBuffer.position() - 1; i++) {
            canvas.drawLine(botLeftXOnView + (i - dataStartIndexInBuffer) * xStep, getYL(dataArr[i], yDataStep),
                    botLeftXOnView + (i - dataStartIndexInBuffer + 1) * xStep, getYL(dataArr[i + 1], yDataStep),
                    linePaint);
        }
    }
    private float getYL(final float yData, float yDataStep) {
        return botLeftYOnView - (yData - yMin) * yDataStep;
    }
}

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