Question

这段代码出了什么问题。当我从上到下播放屏幕时，我希望写入“Down”文本，而不是另一面。但是在模拟器上没有任何变化。问题是什么？

    public class Draw extends View{ 
int ratioX = 50;
int ratioY = 350;
float dx = 0;
float dy = 0;
int newX;
int newY;
String dir="Hello";

public Draw(Context context) {
    super(context);
    // TODO Auto-generated constructor stub
}

public  boolean onTouchEvent(MotionEvent event){
    float touchX = 0;
    float touchY = 0;
    switch(event.getAction()){
    case MotionEvent.ACTION_DOWN:
        touchX = event.getX();
        touchY = event.getY();
        return true;
    case MotionEvent.ACTION_UP:
        dx = touchX - event.getX();
        dy = touchY - event.getY();
        if(Math.abs(dy) > Math.abs(dx)){
            if(dy > 0){
                dir = "DOWN";                
            }
            else{                   
                dir = "UP";                 
            }
        }
        else{
            if(dx > 0){
                dir = "RIGHT";
            }
            else{
                dir = "LEFT";
            }
        }
    }
    return true;
}
public void onDraw(Canvas c){   
    //Rect myRect = new Rect();
    //myRect.set(ratioX,c.getHeight()/8,ratioY,c.getWidth()/8);     
    Paint p = new Paint();
    p.setStyle(Paint.Style.FILL);
    p.setColor(Color.BLACK);
    c.drawPaint(p);     
    //p.setColor(Color.WHITE);
    //c.drawRect(myRect, p);
    p.setColor(Color.WHITE);
    p.setTextSize(18);
    c.drawText(dir, 200, 360, p);
}

}

当我浏览屏幕时没有任何反应！或者我应该使用其他方法？

Answer 1

当您想要更改其内容时，您需要invalidate()您的观点。下面的代码片应该会有所帮助;

public boolean onTouchEvent(MotionEvent event) {
    // Other parts of method omitted for brevity
        case MotionEvent.ACTION_UP:
            dx = touchX - event.getX();
            dy = touchY - event.getY();
            String newDir = dir;
            if(Math.abs(dy) > Math.abs(dx)){
                if(dy > 0){
                    newDir = "DOWN";                
                }
                else{                   
                    newDir = "UP";                 
                }
            }
            else{
                if(dx > 0){
                    newDir = "RIGHT";
                }
                else{
                    newDir = "LEFT";
                }
            }

            if (newDir != dir) {
                dir = newDir;
                // We only want to invalidate the view when your 'dir' value has changed.
                // onDraw() will then be triggered.
                invalidate();
            }
    }
    return true;
}

Answer 2

每次调用onTouchEvent时，本地花车touchX和touchY都会初始化为零。这会对处理ACTION_UP的逻辑产生影响：

dx = touchX - event.getX();
dy = touchY - event.getY();

if(Math.abs(dy) > Math.abs(dx)){
    if(dy > 0){
        dir = "DOWN";                
    } else {                   
        dir = "UP";                 
    }
}

dx和dy最终分别为-x和-y。在Math.abs()来电之后，您实际上是在测试他们的手指是否在屏幕下方比在屏幕上方更远。

将初始向下坐标存储为成员变量，并在ACTION_DOWN期间设置它们。

如何使用onTouchEvent？

2 个答案: