如何在特定位置單擊按鈕繪制圓圈？

Question

我是Android的新手，所以如果我錯過了一些東西，我會提前道歉，但是我的問題是，每次單擊屏幕時，我都試圖在某個位置繪制一個圓圈。

我嘗試了日志記錄，並且確實返回一個與我的if語句匹配的int，但沒有繪制任何內容。

 public boolean onTouchEvent(MotionEvent event) {
        switch (event.getActionMasked()) {
            case MotionEvent.ACTION_DOWN:
                drawCirc = true;
                xTouch = event.getX();
                Log.d("keyboard", "xpos" + xTouch);
                yTouch = event.getY();
                break;

            case MotionEvent.ACTION_UP:
                drawCirc = false;
        }
        return true;
    }


    public void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Paint paint = new Paint();
        paint.setColor(Color.RED);
        if(drawCirc) {
            if (xTouch < 150 && xTouch>0) {
                    paint.setColor(Color.RED);
                    canvas.drawCircle(150, 500, 100, paint);
                    isPlayer1 = false;
                    invalidate();
            }
        }
    }

Answer 1

@Javanator是正確的，您應該invalidate觸摸監聽器invalidate 。

同時，您可以嘗試下面的代碼，該代碼在繪制圓形時會添加動畫。

Paint paint = new Paint();

{
    paint.setColor(Color.RED);
}

// The radius of the circle you want to draw
// 0 by default
private int radius = 0;

// The animator to animate circle drawing
private ObjectAnimator radiusAnimator;

public void setRadius(int newRadius) {
    this.radius = newRadius;
    this.invalidate();
}

private void showCircle(boolean show) {
    ObjectAnimator animator = this.getRadiusAnimator();
    if (show) {
        animator.start();
    } else {
        animator.reverse();
    }
}

private ObjectAnimator getRadiusAnimator() {
    if (this.radiusAnimator == null) {
        this.radiusAnimator = ObjectAnimator.ofInt(this, "radius", 0, 100);
    }
    return this.radiusAnimator;
}


public boolean onTouchEvent(MotionEvent event) {
    switch (event.getActionMasked()) {
        case MotionEvent.ACTION_DOWN:
            // drawCirc = true;
            xTouch = event.getX();
            Log.d("keyboard", "xpos" + xTouch);
            yTouch = event.getY();
            showCircle(true);
            break;

        case MotionEvent.ACTION_UP:
            // drawCirc = false;
            showCircle(false);
    }
    return true;
}


public void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    if (xTouch < 150 && xTouch > 0) {
        canvas.drawCircle(xTouch, yTouch, radius, paint);
    }
    /*
    if(drawCirc) {
        if (xTouch < 150 && xTouch>0) {
                paint.setColor(Color.RED);
                canvas.drawCircle(150, 500, 100, paint);
                isPlayer1 = false;
                invalidate();
    */            
 }

Answer 2

public class CustomView extends View {
boolean drawCirc;
float xTouch;
boolean isPlayer1;
float yTouch;
public CustomView(Context context, AttributeSet attrs) {
    super(context, attrs);
}

public boolean onTouchEvent(MotionEvent event) {
    if (event.getAction() == MotionEvent.ACTION_DOWN) {
        drawCirc=true;
        xTouch = event.getX();
        yTouch = event.getY();
        invalidate();
    }
    return false;
}

@Override
public void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    Paint paint = new Paint();
    paint.setColor(Color.RED);
    if (drawCirc) {
        paint.setColor(Color.RED);
        canvas.drawCircle(xTouch, yTouch, 100, paint);
        isPlayer1 = false;
        invalidate();
    }
}}

我已經解決了您的功能並實現了示例代碼。 我已經檢查了它是否可以正常工作，並且您沒有在onTouch Listener中放入代碼，這就是為什么它不起作用的原因，但是現在我已經解決了。 如果要限制區域，則輸入if (xTouch < 150 && xTouch>0)