我正在尝试使用 onTouch 监听器在 surfaceview 上绘图，但我得到了奇怪的绘图(线条的边缘自行移动)，正如您在下面的 GIF 中看到的那样:

这是我的代码:

public class MainActivity extends AppCompatActivity  implements SurfaceHolder.Callback {

    SurfaceView surfaceView;
    SurfaceHolder surfaceHolder;
    Canvas canvas;
    private Path path;
    Paint mPaint = new Paint();


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate( savedInstanceState );
        setContentView( R.layout.activity_main );

        surfaceView = (SurfaceView) findViewById( R.id.surfaceView );
        surfaceHolder = surfaceView.getHolder();
        surfaceView.getHolder().addCallback( this );

        canvas = surfaceView.getHolder().lockCanvas();

        mPaint = new Paint();
        mPaint.setAntiAlias( true );
        mPaint.setDither( true );
        //  mPaint.setColor(0xff000000);
        mPaint.setStyle( Paint.Style.STROKE );
        mPaint.setStrokeJoin( Paint.Join.ROUND);
        mPaint.setStrokeCap( Paint.Cap.ROUND);
        mPaint.setStrokeWidth( 50);
    }

    @SuppressLint("ClickableViewAccessibility")
    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        Log.d( "surfaceCreated", "surfaceCreated " );


        path = new Path();
        surfaceHolder = holder;
        surfaceView.setOnTouchListener( new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                float X = event.getX();
                float Y = event.getY();
                switch (event.getActionMasked()) {
                    case MotionEvent.ACTION_DOWN:
                        Log.d( "surfaceCreated", "action down x="+X );

//                      canvas = surfaceHolder.lockCanvas();

                        path.moveTo(X,Y);



                        //  mv.touch_start(X,Y);
                        //  canvas = surfaceHolder.lockCanvas();

                        break;
                    case MotionEvent.ACTION_MOVE:
                        Log.d( "surfaceCreated", "action move  x="+X );

                        path.lineTo(X,Y);
                        break;
                    case MotionEvent.ACTION_UP:
                        Log.d( "surfaceCreated", "action up  x="+X );

                        path.lineTo(event.getX(),event.getY());

                        Canvas canvas = surfaceHolder.lockCanvas();
                        canvas.drawPath(path, mPaint);
                        path.reset();
                        surfaceHolder.unlockCanvasAndPost(canvas);

                        //  mCanvas.drawLine( downx, downy, upx, upy, mPaint );
                        break;

                }
                if(path != null){
                    Log.d( "surfaceCreated", "path is not null"+path );
                    Canvas canvas = surfaceHolder.lockCanvas();
                    canvas.drawPath(path, mPaint);
                    surfaceHolder.unlockCanvasAndPost(canvas);
                }
                return true;

            }
        });


    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {

    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {

    }
}

我该如何解决这个问题？以及如何使 surfaceview 变白，正如您看到的，它一开始是黑色的。谢谢!

最佳答案

尝试以下操作:

1)背景问题:

根据:

https://developer.android.com/reference/android/view/SurfaceView

The surface is Z ordered so that it is behind the window holding its SurfaceView; the SurfaceView punches a hole in its window to allow its surface to be displayed. The view hierarchy will take care of correctly compositing with the Surface any siblings of the SurfaceView that would normally appear on top of it. This can be used to place overlays such as buttons on top of the Surface, though note however that it can have an impact on performance since a full alpha-blended composite will be performed each time the Surface changes.

并且基于xav 的 回答:Set the Background Image of a SurfaceView

为了改变你的表面背景颜色，你可以在 surfaceView 的顶部放置一个 View (重叠表面 View )，surfaceHolder 像素格式为透明。

2) 奇怪的绘图问题:“线的边缘自行移动”

您已经得到了答案:感谢 Guillaume Adam

3) Example:

MainActivity.class

public class MainActivity extends AppCompatActivity  implements SurfaceHolder.Callback {

private SurfaceView surfaceView;
private View surfaceBackground;
private Button b_change_surface_background_color;
private Button b_clear;
private Path path;
private Paint mPaint = new Paint();
private int[] colors = new int[]{Color.WHITE, Color.GREEN, Color.MAGENTA, Color.BLUE};
private int currentSurfaceBackgroundColor = Color.WHITE;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    b_change_surface_background_color = (Button) findViewById(R.id.b_change_surface_background_color);
    b_change_surface_background_color.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            int colorIndex = new Random().nextInt(colors.length);
            currentSurfaceBackgroundColor = colors[colorIndex];
            changeSurfaceBackgroundColor(currentSurfaceBackgroundColor);
        }
    });

    surfaceView = (SurfaceView) findViewById(R.id.surfaceView);
    surfaceView.setZOrderOnTop(true);
    surfaceView.getHolder().setFormat(PixelFormat.TRANSPARENT);
    surfaceView.getHolder().addCallback(this);

    surfaceBackground = (View) findViewById(R.id.surfaceBackground);

    mPaint = new Paint();
    mPaint.setAntiAlias(true);
    mPaint.setDither(true);
    mPaint.setColor(Color.BLACK);
    mPaint.setStyle(Paint.Style.STROKE);
    mPaint.setStrokeJoin(Paint.Join.ROUND);
    mPaint.setStrokeCap(Paint.Cap.ROUND);
    mPaint.setStrokeWidth(50);
}

@SuppressLint("ClickableViewAccessibility")
@Override
public void surfaceCreated(SurfaceHolder holder) {
    path = new Path();
    surfaceView.setOnTouchListener(new View.OnTouchListener() {
        @Override
        public boolean onTouch(View v, MotionEvent event) {
            float X = event.getX();
            float Y = event.getY();
            switch (event.getActionMasked()) {
                case MotionEvent.ACTION_DOWN:
                    path.reset();
                    path.moveTo(X, Y);
                    break;
                case MotionEvent.ACTION_MOVE:
                    path.lineTo(X, Y);
                    break;
                case MotionEvent.ACTION_UP:
                    path.lineTo(event.getX(),event.getY());
                    Canvas canvas1 = surfaceView.getHolder().lockCanvas();
                    canvas1.drawPath(path, mPaint);
                    surfaceView.getHolder().unlockCanvasAndPost(canvas1);
                    break;

            }
            if(path != null){
                Canvas canvas = surfaceView.getHolder().lockCanvas();
                canvas.drawPath(path, mPaint);
                surfaceView.getHolder().unlockCanvasAndPost(canvas);
            }
            return true;

        }
    });


}

@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {

}

@Override
public void surfaceDestroyed(SurfaceHolder holder) {

}

private void changeSurfaceBackgroundColor(@ColorInt int color) {
    if (surfaceBackground != null) {
        surfaceBackground.setBackgroundColor(color);
    }
}

}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/rl"
android:layout_width="match_parent"
android:layout_height="match_parent">

<Button
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Change Surface Background Color"
    android:textAllCaps="false"
    android:layout_alignParentTop="true"
    android:id="@+id/b_change_surface_background_color">
</Button>

<SurfaceView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_below="@id/b_change_surface_background_color"
    android:id="@+id/surfaceView">
</SurfaceView>

<View
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/surfaceBackground"
    android:layout_below="@id/b_change_surface_background_color"
    android:background="@android:color/white">
</View>

</RelativeLayout>

4) Output

关于android - 在 SurfaceView 上绘图，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/57742739/