在拖动视图的任何位置在画布上绘制

Question

我正在尝试使用画布创建一个简单的绘画应用程序。最终产品是让用户选择选择的工具(笔、记号笔、橡皮擦等(，并在画布上拖动工具的任何位置相应地绘制或擦除。

截至目前，我只有一支笔，我正在尝试在画布中拖动笔的任何地方画一条线。但是，我发现这项任务具有挑战性。我可以拖动笔，可以画线，但是在拖动笔时不能画。我正在联系SO社区以弥合这两个功能。

以下是我所拥有的：

主要活动.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);
CanvasView canvasView = new CanvasView(MainActivity.this);
w1 = (ImageView) findViewById(R.id.wand1);
pl = (RelativeLayout) findViewById(R.id.coordAct);
RelativeLayout rootLayout = (RelativeLayout) findViewById(R.id.coordAct);
rootLayout.addView(canvasView);
RelativeLayout.LayoutParams layoutParams1w2 = new RelativeLayout.LayoutParams(getScreenWidth(), getScreenHeight() / 2);
layoutParams1w2.addRule(RelativeLayout.CENTER_IN_PARENT, RelativeLayout.TRUE);
canvasView.setLayoutParams(layoutParams1w2);
w1.setOnTouchListener(new ChoiceTouchListener());
}
public static int getScreenWidth() {
return Resources.getSystem().getDisplayMetrics().widthPixels;
}
public static int getScreenHeight() {
return Resources.getSystem().getDisplayMetrics().heightPixels;
}
public 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;
}
}

画布视图.java

public class CanvasView extends View{
Context context;
int width, height;
Bitmap bitmap;
Path path;
Canvas canvas;
Paint paint;
float mX, mY;
static final float TOLERANCE=4;
public CanvasView(Context context) {
super(context);
this.context=context;
path=new Path();
paint = new Paint();
paint.setAntiAlias(true);
paint.setColor(Color.BLACK);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeJoin(Paint.Join.ROUND);
paint.setStrokeWidth(50);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w,h,oldw,oldh);
bitmap=Bitmap.createBitmap(w,h,Bitmap.Config.ARGB_8888);
canvas=new Canvas(bitmap);
}
public void startTouch(float x, float y) {
path.moveTo(x, y);
mX = x;
mY = y;
}
public void moveTouch(float x, float y) {
float dx = Math.abs(x-mX);
float dy = Math.abs(y-mY);
if(dx>=TOLERANCE || dy>= TOLERANCE) {
path.quadTo(mX, mY, (x+mX)/2, (y+mY)/2);
mX=x;
mY=y;
}
}
//To clear canvas
public void clearCanvas() {
path.reset();
invalidate();
}
public void upTouch() {
path.lineTo(mX,mY);
}
@Override
protected void onDraw(Canvas canvas){
super.onDraw(canvas);
canvas.drawPath(path,paint);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
float x = event.getX();
float y = event.getY();
switch (event.getAction())
{
case MotionEvent.ACTION_DOWN:
startTouch(x,y);
invalidate();
break;
case MotionEvent.ACTION_MOVE:
moveTouch(x,y);
invalidate();
break;
case MotionEvent.ACTION_UP:
upTouch();
invalidate();
break;
default:
return false;
}
invalidate();
return true;
}

activity_main.xml

<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"
tools:context="com.simplepaintapp.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/pen" />

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

</RelativeLayout>

在 onTouch(( 中实现 dispatchTouchEvent(( 方法后的当前错误

Answer 1

需要更新 MainActivity 和 CanvasView。请参阅下面的新源代码：

主要活动.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;
CanvasView canvasView;
public static int X;
public static int Y;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
canvasView = new CanvasView(MainActivity.this);
w1 = (ImageView) findViewById(R.id.wand1);
pl = (RelativeLayout) findViewById(R.id.coordAct);
RelativeLayout rootLayout = (RelativeLayout) findViewById(R.id.coordAct);
rootLayout.addView(canvasView);
RelativeLayout.LayoutParams layoutParams1w2 = new RelativeLayout.LayoutParams(getScreenWidth(), getScreenHeight() / 2);
layoutParams1w2.addRule(RelativeLayout.CENTER_IN_PARENT, RelativeLayout.TRUE);
canvasView.setLayoutParams(layoutParams1w2);
w1.setOnTouchListener(new ChoiceTouchListener());
}
public static int getScreenWidth() {
return Resources.getSystem().getDisplayMetrics().widthPixels;
}
public static int getScreenHeight() {
return Resources.getSystem().getDisplayMetrics().heightPixels;
}
public 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;
}
X = (int) event.getRawX();
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;
canvasView.dispatchTouchEvent(event);
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);
canvasView.dispatchTouchEvent(event);
break;
}
rootLayout.invalidate();
return true;
}
}

画布视图.java：

public class CanvasView extends View{
Context context;
int width, height;
Bitmap bitmap;
Path path;
public Canvas canvas;
Paint paint;
float mX, mY;
static final float TOLERANCE=4;
public static float x;
public static float y;
public CanvasView(Context context) {
super(context);
this.context=context;
path=new Path();
paint = new Paint();
paint.setAntiAlias(true);
paint.setColor(Color.BLACK);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeJoin(Paint.Join.ROUND);
paint.setStrokeWidth(50);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w,h,oldw,oldh);
bitmap=Bitmap.createBitmap(w,h,Bitmap.Config.ARGB_8888);
canvas=new Canvas(bitmap);
}
public void startTouch(float x, float y) {
path.moveTo(x, y);
mX = x;
mY = y;
}
public void moveTouch(float x, float y) {
float dx = Math.abs(x-mX);
float dy = Math.abs(y-mY);
if(dx>=TOLERANCE || dy>= TOLERANCE) {
path.quadTo(mX, mY, (x+mX)/2, (y+mY)/2);
mX=x;
mY=y;
}
}
//To clear canvas
public void clearCanvas() {
path.reset();
invalidate();
}
public void upTouch() {
path.lineTo(mX,mY);
}
@Override
protected void onDraw(Canvas canvas){
super.onDraw(canvas);
canvas.drawPath(path,paint);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
float x = event.getX();
float y = event.getY();
switch (event.getAction())
{
case MotionEvent.ACTION_DOWN:
startTouch(MainActivity.X,MainActivity.Y-380);
invalidate();
break;
case MotionEvent.ACTION_MOVE:
moveTouch(MainActivity.X,MainActivity.Y-380);
invalidate();
break;
case MotionEvent.ACTION_UP:
upTouch();
invalidate();
break;
default:
return false;
}
invalidate();
return true;
}