Android中的Compass(羅盤) 詳解

Compass(羅盤)是一個定制的視圖, 繼承View類, 重寫了視圖的邊界(onMeasure)和內容(onDraw);

如圖:

以下是Compass的具體設計:

1. 創建CompassView類, 羅盤視圖

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); //筆畫寬度  
        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); //相反方向旋轉  
      
        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;  
    }  
}

這個類代碼較多, 詳解:

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