Android自定义视图绘图

Posted 2023-01-14

android自定义视图绘图：屏幕截图：

这不能保存最后一个跟踪，我想重绘一个位图，但效果不是很好。

截图：

码：

public class CustomView extends View 

private float sX, sY, eX, eY;

private Paint paint = new Paint();
private Canvas canvas = new Canvas();
private Bitmap bitmap;

@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) 
    super.onSizeChanged(w, h, oldw, oldh);
    bitmap = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888);
    canvas.setBitmap(bitmap);
    setBackgroundColor(Color.WHITE);


@Override
public boolean onTouchEvent(MotionEvent event) 
    switch (event.getAction()) 
        case MotionEvent.ACTION_MOVE:
            eX = event.getX();
            eY = event.getY();
            canvas.drawLine(sX, sY, eX, eY, paint);
            break;
        case MotionEvent.ACTION_DOWN:
            sX = event.getX();
            sY = event.getY();
            break;
        case MotionEvent.ACTION_UP:
            break;
    
    invalidate();
    return true;


@Override
protected void onDraw(Canvas canvas) 
    super.onDraw(canvas);
    canvas.drawBitmap(bitmap, getMatrix(), null);

你遇到过同样的问题吗？

答案

我找到了解决方案，但我不想以这种方式解决问题。我的目标是只用新画布来解决问题。

screenshot

public class CustomView extends View 

private float sX, sY, eX, eY;

private Paint paint = new Paint();
private Canvas canvas = new Canvas();
private Bitmap bitmap;

public CustomView(Context context) 
    super(context);
    init();


public CustomView(Context context, AttributeSet attrs) 
    super(context, attrs);
    init();


public CustomView(Context context, AttributeSet attrs, int defStyleAttr) 
    super(context, attrs, defStyleAttr);
    init();


private void init() 
    paint.setColor(Color.RED);
    paint.setStrokeWidth(3);
    paint.setAntiAlias(true);
    paint.setDither(true);
    paint.setStrokeJoin(Paint.Join.ROUND);
    paint.setStrokeCap(Paint.Cap.ROUND);
    paint.setStyle(Paint.Style.STROKE);


@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) 
    super.onSizeChanged(w, h, oldw, oldh);
    bitmap = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888);
    canvas.setBitmap(bitmap);
    setBackgroundColor(Color.WHITE);


@Override
public boolean onTouchEvent(MotionEvent event) 
    switch (event.getAction()) 
        case MotionEvent.ACTION_MOVE:
            eX = event.getX();
            eY = event.getY();
            break;
        case MotionEvent.ACTION_DOWN:
            sX = event.getX();
            sY = event.getY();
            break;
        case MotionEvent.ACTION_UP:
            canvas.drawLine(sX, sY, eX, eY, paint);
            break;
    
    invalidate();
    return true;


@Override
protected void onDraw(Canvas canvas) 
    super.onDraw(canvas);
    canvas.drawBitmap(bitmap, getMatrix(), null);
    canvas.drawLine(sX, sY, eX, eY, paint);

要么

public class CustomView extends View 

private Paint paint = new Paint();
private List<Path> cache = new ArrayList<>();
private Path currentPath;

public CustomView(Context context) 
    super(context);
    init();


public CustomView(Context context, AttributeSet attrs) 
    super(context, attrs);
    init();


public CustomView(Context context, AttributeSet attrs, int defStyleAttr) 
    super(context, attrs, defStyleAttr);
    init();


private void init() 
    paint.setColor(Color.RED);
    paint.setStrokeWidth(3);
    paint.setAntiAlias(true);
    paint.setDither(true);
    paint.setStrokeJoin(Paint.Join.ROUND);
    paint.setStrokeCap(Paint.Cap.ROUND);
    paint.setStyle(Paint.Style.STROKE);


@Override
public boolean onTouchEvent(MotionEvent event) 
    switch (event.getAction()) 
        case MotionEvent.ACTION_MOVE:
            if (currentPath != null) 
                currentPath.eX = event.getX();
                currentPath.eY = event.getY();
            
            break;
        case MotionEvent.ACTION_DOWN:
            currentPath = new Path();
            currentPath.sX = event.getX();
            currentPath.sY = event.getY();
            break;
        case MotionEvent.ACTION_UP:
            if (currentPath != null) 
                cache.add(currentPath);
                currentPath = null;
            
            break;

    
    invalidate();
    return true;


@Override
protected void onDraw(Canvas canvas) 
    super.onDraw(canvas);
    for (Path path : cache) 
        canvas.drawLine(path.sX, path.sY, path.eX, path.eY, paint);
    
    if (currentPath == null) return;
    canvas.drawLine(currentPath.sX, currentPath.sY, currentPath.eX, currentPath.eY, paint);


static class Path 
    float sX;
    float sY;
    float eX;
    float eY;

另一答案

当你的手指移动时，你应该更新sX sY变量

1. ACTION_DOWN点是[100,100] sX = 100，sY = 100
2. ACTION_MOVE现在手指位于[130,150] eY = 130，eY = 150
3. invalidate()所以将触发draw()画线[100,100]到[130,150]
4. 手指继续移动
5. ACTION_MOVE现在开始是[130,150] sX = 130，sY = 150不是ACTION_DOWN点值
6. ACTION_MOVE现在手指位于[160,180]
7. invalidate()所以将触发draw()画线[130,150]到[160,180]
8. 继续做同样的事情.....

@Override
public boolean onTouchEvent(MotionEvent event) 
    switch (event.getAction()) 
        case MotionEvent.ACTION_MOVE:
            eX = event.getX();
            eY = event.getY();
            invalidate()
            sX = eX;
            sY = eY;
            break;
        case MotionEvent.ACTION_DOWN:
            sX = event.getX();
            sY = event.getY();
            break;
        case MotionEvent.ACTION_UP:
            canvas.drawLine(sX, sY, eX, eY, paint);
            break;
    
    //invalidate();
    return true;

我没有运行代码，但也许你已经明白了我的意思。

你应该更新startX startY和endX endY