Question

对于一个小项目，我必须编写一个Android应用程序，用手指在屏幕上画一条线。目前我使用这段代码

´
public class MainActivity extends Activity {

   DrawingView dv ;   
   private Paint       mPaint;


   @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    dv = new DrawingView(this);
    setContentView(dv);
    mPaint = new Paint();
    mPaint.setAntiAlias(true);
    mPaint.setDither(true);
    mPaint.setColor(Color.GREEN);
    mPaint.setStyle(Paint.Style.STROKE);
    mPaint.setStrokeJoin(Paint.Join.ROUND);
    mPaint.setStrokeCap(Paint.Cap.ROUND);
    mPaint.setStrokeWidth(12);  
}

 public class DrawingView extends View {

    public int width;
    public  int height;
    private Bitmap  mBitmap;
    private Canvas  mCanvas;
    private Path    mPath;
    private Paint   mBitmapPaint;
    Context context;
    private Paint circlePaint;
    private Path circlePath;

    public DrawingView(Context c) {
    super(c);
    context=c;
    mPath = new Path();
    mBitmapPaint = new Paint(Paint.DITHER_FLAG);  
    circlePaint = new Paint();
    circlePath = new Path();
    circlePaint.setAntiAlias(true);
    circlePaint.setColor(Color.BLUE);
    circlePaint.setStyle(Paint.Style.STROKE);
    circlePaint.setStrokeJoin(Paint.Join.MITER);
    circlePaint.setStrokeWidth(4f); 


    }

    @Override
     protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    super.onSizeChanged(w, h, oldw, oldh);

    mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
    mCanvas = new Canvas(mBitmap);

    }
    @Override
    protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    canvas.drawBitmap( mBitmap, 0, 0, mBitmapPaint);

    canvas.drawPath( mPath,  mPaint);

    canvas.drawPath( circlePath,  circlePaint);
    }

    private float mX, mY;
    private static final float TOUCH_TOLERANCE = 4;

    private void touch_start(float x, float y) {
    mPath.reset();
    mPath.moveTo(x, y);
    mX = x;
    mY = y;
    }
    private void touch_move(float x, float y) {
    float dx = Math.abs(x - mX);
    float dy = Math.abs(y - mY);
    if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
         mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
        mX = x;
        mY = y;

        circlePath.reset();
        circlePath.addCircle(mX, mY, 30, Path.Direction.CW);
    }
    }
    private void touch_up() {
    mPath.lineTo(mX, mY);
    circlePath.reset();
    // commit the path to our offscreen
    mCanvas.drawPath(mPath,  mPaint);
    // kill this so we don't double draw
    mPath.reset();
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
    float x = event.getX();
    float y = event.getY();

    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            touch_start(x, y);
            invalidate();
            break;
        case MotionEvent.ACTION_MOVE:
            touch_move(x, y);
            invalidate();
            break;
        case MotionEvent.ACTION_UP:
            touch_up();
            invalidate();
            break;
    }
    return true;
    }  
    }

}

有了这个，我可以在我的屏幕上画一条线，但我不知道如何将画线转换为位图。我想我理解错了，但我认为“mBitmap”只是一个空的Bitmap，“picture”保存在“mCanvas”中。

那么有没有办法在Bitmap中转换画线？

Answer 1

您无需为此创建mBitmap或mCanvas。您只需致电View.getDrawingCache()即可获取View的内容。 More info here

但是如果您打算使用自己的位图进行绘制，则需要mBitmap和mCanvas。请按照以下步骤完成此操作：

将以下行移动到构造函数中，因为您只想创建一次位图和画布。

mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
mCanvas = new Canvas(mBitmap);

在onDraw()方法中，使用mCanvas绘制而不是canvas。最后将mBitmap绘制到视图的画布上。如下所示：

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    // This will use the mCanvas and draw the `path` in the mBitmap.
    mCanvas.drawPath( mPath,  mPaint);
    mCanvas.drawPath( circlePath,  circlePaint);

    // Now once everything is drawn on mBitmap, we will draw the contents of this mBitmap onto the underlying bitmap of the View via `canvas`.
    canvas.drawBitmap( mBitmap, 0, 0, mBitmapPaint);
}

永远记住，每个视图都有一个底层位图（共享）。您在canvas中获得的onDraw()将帮助您在基础位图中绘制内容。如果要绘制自己的位图，则需要创建位图和画布，并使用您创建的画布进行绘制，而不是onDraw()中提供给您的画布。

Android Studio | Java ---用手指画一个位图

1 个答案: