我想知道如何在ImageView上随着用户滑动手指来绘制一条直线?
有人能解释一下吗?或者提供任何开始的链接。
你需要拥有自己的ImageView并重写onDraw函数。可以使用类似以下代码:
public class MyImageView extends ImageView{
public MyImageView(Context context) {
super(context);
// TODO Auto-generated constructor stub
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
Paint p = new Paint(Paint.ANTI_ALIAS_FLAG);
canvas.drawLine(0, 0, 20, 20, p);
}
}
在您的主类中创建对象MyImageView
;当您触摸屏幕时调用update();
函数。
Paint p
添加为类的属性,然后在类构造函数中初始化它,最后将super.onDraw(canvas);
移动到您的绘图操作之上。这将允许您在原始图像上进行绘制。 - Nuxpackage CustomWidgets;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.util.AttributeSet;
/**
* Allows to draw rectangle on ImageView.
*
* @author Maciej Nux Jaros
*/
public class DrawImageView extends ImageView {
private Paint currentPaint;
public boolean drawRect = false;
public float left;
public float top;
public float right;
public float bottom;
public DrawImageView(Context context, AttributeSet attrs) {
super(context, attrs);
currentPaint = new Paint();
currentPaint.setDither(true);
currentPaint.setColor(0xFF00CC00); // alpha.r.g.b
currentPaint.setStyle(Paint.Style.STROKE);
currentPaint.setStrokeJoin(Paint.Join.ROUND);
currentPaint.setStrokeCap(Paint.Cap.ROUND);
currentPaint.setStrokeWidth(2);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
if (drawRect)
{
canvas.drawRect(left, top, right, bottom, currentPaint);
}
}
}
<CustomWidgets.DrawImageView
android:id="@+id/widgetMap"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:src="@drawable/map_small"
/>
然后,您可以在控制布局的活动的触摸事件中使用此示例:
mapImageView.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
DrawImageView drawView = (DrawImageView) v;
// set start coords
if (event.getAction() == MotionEvent.ACTION_DOWN) {
drawView.left = event.getX();
drawView.top = event.getY();
// set end coords
} else {
drawView.right = event.getX();
drawView.bottom = event.getY();
}
// draw
drawView.invalidate();
drawView.drawRect = true;
return true;
}
});
要绘制用户实际绘制的线条,您必须重写dispatchTouchEvent。从该事件中,您可以获取线条的坐标,并在onDraw中绘制它们,如George所示。