Android中的Compass(罗盘) 详解

Compass(罗盘)是一个定制的视图, 继承View类, 重写了视图的边界(onMeasure)和内容(onDraw);

如图:

以下是Compass的具体设计:

1. 创建CompassView类, 罗盘视图

位置: java->package->CompassView

package mzx.spike.compass.app;  

import android.content.Context;
import android.content.res.Resources;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;
import android.view.accessibility.AccessibilityEvent;  

/**
 * Created by C.L.Wang on 14-3-16.
 */
public class CompassView extends View {  

    private float bearing; //方位  

    public void setBearing(float _bearing) {
        bearing = _bearing;
        sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_TEXT_CHANGED);
    }  

    public float getBearing() {
        return bearing;
    }  

    private Paint markerPaint;
    private Paint textPaint;
    private Paint circlePaint;
    private String northString;
    private String eastString;
    private String southString;
    private String westString;
    private int textHeight;  

    public CompassView(Context context) {
        super(context);
        initCompassView();
    }  

    public CompassView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initCompassView();
    }  

    public CompassView(Context context, AttributeSet attrs, int defaultStyle) {
        super(context, attrs, defaultStyle);
        initCompassView();
    }  

    private void initCompassView() {
        setFocusable(true);  

        Resources r = this.getResources();  

        circlePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        circlePaint.setColor(r.getColor(R.color.background_color));
        circlePaint.setStrokeWidth(1); //笔画宽度
        circlePaint.setStyle(Paint.Style.FILL_AND_STROKE);  

        northString = r.getString(R.string.cardinal_north);
        eastString = r.getString(R.string.cardinal_east);
        southString = r.getString(R.string.cardinal_south);
        westString = r.getString(R.string.cardinal_west);  

        textPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        textPaint.setColor(r.getColor(R.color.text_color));  

        textHeight = (int)textPaint.measureText("yY");  

        markerPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        markerPaint.setColor(r.getColor(R.color.marker_color));
    }  

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int measuredWidth = measure(widthMeasureSpec);
        int measuredHeight = measure(heightMeasureSpec);  

        int d = Math.min(measuredWidth, measuredHeight);  

        setMeasuredDimension(d, d);
    }  

    protected int measure(int measureSpec) {
        int result;  

        int specMode = MeasureSpec.getMode(measureSpec);
        int specSize = MeasureSpec.getSize(measureSpec);  

        if (specMode == MeasureSpec.UNSPECIFIED) {
            result = 200;
        } else {
            result = specSize;
        }  

        return result;
    }  

    @Override
    protected void onDraw(Canvas canvas) {
        int mMeasuredWidth = getMeasuredWidth();
        int mMeasuredHeight = getMeasuredHeight();  

        int px = mMeasuredWidth/2;
        int py = mMeasuredHeight/2;  

        int radius = Math.min(px, py);  

        canvas.drawCircle(px, py, radius, circlePaint);  

        canvas.save();
        canvas.rotate(-bearing, px, py); //相反方向旋转  

        int textWidth = (int)textPaint.measureText("W");
        int cardinalX = px-textWidth/2;
        int cardinalY = py-radius+textHeight;  

        for (int i=0; i<24; i++) {
            canvas.drawLine(px, py-radius, px, py-radius+10, markerPaint);  

            canvas.save();
            canvas.translate(0, textHeight);  

            if (i%6 == 0) {
                String dirString = "";
                switch (i) {
                    case (0) : {
                        dirString = northString;
                        int arrowY = 2*textHeight;
                        canvas.drawLine(px, arrowY, px-5, 3*textHeight, markerPaint);
                        canvas.drawLine(px, arrowY, px+5, 3*textHeight, markerPaint);
                        break;
                    }  

                    case (6) : dirString = eastString; break;
                    case (12) : dirString = southString; break;
                    case (18) : dirString = westString; break;
                }  

                canvas.drawText(dirString, cardinalX, cardinalY, textPaint);
            }  

            else if (i%3 == 0) {
                String angle = String.valueOf(i*15);
                float angleTextWidth = textPaint.measureText(angle);  

                int angleTextX = (int)(px-angleTextWidth/2);
                int angleTextY = py-radius+textHeight;
                canvas.drawText(angle, angleTextX, angleTextY, textPaint);
            }  

            canvas.restore();  

            canvas.rotate(15, px, py);
        }
        canvas.restore();
    }  

    @Override
    public boolean dispatchPopulateAccessibilityEvent(final AccessibilityEvent event) {
        super.dispatchPopulateAccessibilityEvent(event);  

        if (isShown()) {
            String bearingStr = String.valueOf(bearing);  

            event.getText().add(bearingStr);  

            return true;
        } else
            return false;
    }
}

这个类代码较多, 详解:

查看本栏目更多精彩内容：http://www.bianceng.cnhttp://www.bianceng.cn/OS/extra/

以上是小编为您精心准备的的内容，在的博客、问答、公众号、人物、课程等栏目也有的相关内容，欢迎继续使用右上角搜索按钮进行搜索android
， android canvas
， int
， private
， context
， compass
， import
， paint
， views py
， #电子罗盘
， android中context详解
， android中的context
onMeasure
compass 罗盘信息、android compass、中国罗盘详解、罗盘详解、风水罗盘盘面详解，以便于您获取更多的相关知识。