使用可拖动对象擦除

Question

我正在尝试创建一个可以删除图像部分的Android应用程序。我试图通过使用可拖动对象（橡皮擦图像）来实现这一目标。

我已经实现了将橡皮擦图像拖动到应用程序中的任何位置并在拖动手指时擦除背景图像的功能。现在我想桥接这两个功能，以便仅在拖动橡皮擦图像时擦除背景图像。我怎样才能完成这项任务？

以下是我到目前为止所做的事情：

MainActivity.java

public class MainActivity extends AppCompatActivity {
private ViewGroup rootLayout;
private int _xDelta;
private int _yDelta;
private RelativeLayout pl;
private ImageView w1;
private boolean clicked1 = false;

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

    MyCustomView myCustomView = new MyCustomView(MainActivity.this);

    w1 = (ImageView) findViewById(R.id.wand1);
    pl = (RelativeLayout) findViewById(R.id.coordAct);
    RelativeLayout rootLayout = (RelativeLayout) findViewById(R.id.coordAct);

    rootLayout.addView(myCustomView);

    RelativeLayout.LayoutParams layoutParams1w2 = new RelativeLayout.LayoutParams(getScreenWidth(), getScreenHeight() / 2);
    layoutParams1w2.addRule(RelativeLayout.CENTER_IN_PARENT, RelativeLayout.TRUE);
    myCustomView.setLayoutParams(layoutParams1w2);

    w1.setOnTouchListener(new ChoiceTouchListener());
}

public static int getScreenWidth() {
    return Resources.getSystem().getDisplayMetrics().widthPixels;
}

public static int getScreenHeight() {
    return Resources.getSystem().getDisplayMetrics().heightPixels;
}

private final class ChoiceTouchListener implements View.OnTouchListener {
    public boolean onTouch(View view, MotionEvent event) {
        if (!clicked1){
            rootLayout = (ViewGroup) w1.getParent();
            if (rootLayout != null) {
                // detach the child from parent
                rootLayout.removeView(w1);
            }
            RelativeLayout.LayoutParams layoutParams1 = new RelativeLayout.LayoutParams(300, 300);
            pl.addView(w1);

            w1.setLayoutParams(layoutParams1);
            clicked1 = true;
        }
        final int X = (int) event.getRawX();
        final int Y = (int) event.getRawY();

        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_DOWN:
                RelativeLayout.LayoutParams lParams = (RelativeLayout.LayoutParams) view.getLayoutParams();
                _xDelta = X - lParams.leftMargin;
                _yDelta = Y - lParams.topMargin;
                break;
            case MotionEvent.ACTION_MOVE:
                RelativeLayout.LayoutParams layoutParams = (RelativeLayout.LayoutParams) view
                        .getLayoutParams();
                layoutParams.leftMargin = X - _xDelta;
                layoutParams.topMargin = Y - _yDelta;
                layoutParams.rightMargin = -250;
                layoutParams.bottomMargin = -250;
                view.setLayoutParams(layoutParams);
                break;
        }
        rootLayout.invalidate();
        return true;
    }
}

MyCustomView.java

public class MyCustomView extends View {

private Bitmap sourceBitmap;
private Canvas sourceCanvas = new Canvas();
private Paint destPaint = new Paint();
private Path destPath = new Path();

public MyCustomView(Context context) {
    super(context);

    //converting drawable resource file into bitmap
    Bitmap rawBitmap = BitmapFactory.decodeResource(context.getResources(), R.mipmap.armissueserase);

    //converting bitmap into mutable bitmap
    sourceBitmap = Bitmap.createBitmap(rawBitmap.getWidth(), rawBitmap.getHeight(), Bitmap.Config.ARGB_8888);

    sourceCanvas.setBitmap(sourceBitmap);
    sourceCanvas.drawBitmap(rawBitmap, 0, 0, null);

    destPaint.setAlpha(0);
    destPaint.setAntiAlias(true);
    destPaint.setStyle(Paint.Style.STROKE);
    destPaint.setStrokeJoin(Paint.Join.ROUND);
    destPaint.setStrokeCap(Paint.Cap.ROUND);
    //change this value as per your need
    destPaint.setStrokeWidth(50);
    destPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
}

@Override
protected void onDraw(Canvas canvas) {
    sourceCanvas.drawPath(destPath, destPaint);
    canvas.drawBitmap(sourceBitmap, 0, 0, null);
    super.onDraw(canvas);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    float xPos = event.getX();
    float yPos = event.getY();

    switch (event.getAction())
    {
        case MotionEvent.ACTION_DOWN:
            destPath.moveTo(xPos, yPos);
            break;
        case MotionEvent.ACTION_MOVE:
            destPath.lineTo(xPos, yPos);
            break;
        default:
            return false;
    }
    invalidate();
    return true;
}

activity_main.xml中

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/coordAct"
android:background="@drawable/background"
tools:context="com.erasewithtouch.MainActivity">

<RelativeLayout
    android:id="@+id/parLayout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:weightSum="3"
    android:background="#0000ff">



    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="100dp"
        android:layout_alignParentBottom="true"
        android:layout_alignParentStart="true"
        android:layout_marginBottom="28dp"
        android:background="#BA9DF7"
        android:gravity="bottom"
        android:orientation="vertical">

        <HorizontalScrollView
            android:id="@+id/backgd"
            android:layout_width="match_parent"
            android:layout_height="100dp"
            android:weightSum="1">

            <LinearLayout
                android:id="@+id/parentLL"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_weight="1"
                android:orientation="horizontal"
                android:weightSum="5">


                    <ImageView
                        android:id="@+id/wand1"
                        android:layout_width="100dp"
                        android:layout_height="100dp"
                        android:layout_centerInParent="true"
                        android:layout_gravity="center"
                        android:src="@drawable/wand1" />


            </LinearLayout>
        </HorizontalScrollView>
    </RelativeLayout>


</RelativeLayout>

非常感谢任何帮助。谢谢！