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還有其他幾個類似於我的問題，我已經按照每種可能的方式執行了他們的答案，但這似乎不適用於我的代碼。我接近解決方案，但似乎缺少的東西。請幫忙，我要求不要將問題標記爲重複。在Android畫布上取消功能
這裏是在MainActivity：
public class MainActivity extends Activity implements View.OnClickListener {
// private ArrayList<Path> paths = new ArrayList<Path>();
// private ArrayList<Path> undonePaths = new ArrayList<Path>();
private Button btnUndo;
public DrawingView drawView;
//buttons
private ImageButton currPaint, drawBtn, eraseBtn, newBtn, saveBtn, opacityBtn;
//sizes
private float smallBrush, mediumBrush, largeBrush;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
drawView = (DrawingView) findViewById(R.id.drawing);
//get the palette and first color button
LinearLayout paintLayout = (LinearLayout) findViewById(R.id.paint_colors);
currPaint = (ImageButton) paintLayout.getChildAt(0);
currPaint.setImageDrawable(getResources().getDrawable(R.drawable.paint_pressed));
//sizes from dimensions
smallBrush = 10;
mediumBrush = 20;
largeBrush = 30;
//draw button
drawBtn = (ImageButton) findViewById(R.id.draw_btn);
drawBtn.setOnClickListener(this);
//set initial size
drawView.setBrushSize(mediumBrush);
//erase button
eraseBtn = (ImageButton) findViewById(R.id.erase_btn);
eraseBtn.setOnClickListener(this);
//new button
newBtn = (ImageButton) findViewById(R.id.new_btn);
newBtn.setOnClickListener(this);
//save button
saveBtn = (ImageButton) findViewById(R.id.save_btn);
saveBtn.setOnClickListener(this);
//opacity
opacityBtn = (ImageButton) findViewById(R.id.opacity_btn);
opacityBtn.setOnClickListener(this);
btnUndo = (Button) findViewById(R.id.btnUndo);
btnUndo.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
drawView.undo();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
//user clicked paint
public void paintClicked(View view) {
//use chosen color
//set erase false
drawView.setErase(false);
drawView.setPaintAlpha(100);
drawView.setBrushSize(drawView.getLastBrushSize());
if (view != currPaint) {
ImageButton imgView = (ImageButton) view;
String color = view.getTag().toString();
drawView.setColor(color);
//update ui
imgView.setImageDrawable(getResources().getDrawable(R.drawable.paint_pressed));
currPaint.setImageDrawable(getResources().getDrawable(R.drawable.paint));
currPaint = (ImageButton) view;
}
}
@Override
public void onClick(View view) {
if (view.getId() == R.id.draw_btn) {
//draw button clicked
final Dialog brushDialog = new Dialog(this);
brushDialog.setTitle("Brush size:");
brushDialog.setContentView(R.layout.brush_chooser);
//listen for clicks on size buttons
ImageButton smallBtn = (ImageButton) brushDialog.findViewById(R.id.small_brush);
smallBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
drawView.setErase(false);
drawView.setBrushSize(smallBrush);
drawView.setLastBrushSize(smallBrush);
brushDialog.dismiss();
}
});
ImageButton mediumBtn = (ImageButton) brushDialog.findViewById(R.id.medium_brush);
mediumBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
drawView.setErase(false);
drawView.setBrushSize(mediumBrush);
drawView.setLastBrushSize(mediumBrush);
brushDialog.dismiss();
}
});
ImageButton largeBtn = (ImageButton) brushDialog.findViewById(R.id.large_brush);
largeBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
drawView.setErase(false);
drawView.setBrushSize(largeBrush);
drawView.setLastBrushSize(largeBrush);
brushDialog.dismiss();
}
});
//show and wait for user interaction
brushDialog.show();
}
else if (view.getId() == R.id.erase_btn) {
//switch to erase - choose size
final Dialog brushDialog = new Dialog(this);
brushDialog.setTitle("Eraser size:");
brushDialog.setContentView(R.layout.brush_chooser);
//size buttons
ImageButton smallBtn = (ImageButton) brushDialog.findViewById(R.id.small_brush);
smallBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
drawView.setErase(true);
drawView.setBrushSize(smallBrush);
brushDialog.dismiss();
}
});
ImageButton mediumBtn = (ImageButton) brushDialog.findViewById(R.id.medium_brush);
mediumBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
drawView.setErase(true);
drawView.setBrushSize(mediumBrush);
brushDialog.dismiss();
}
});
ImageButton largeBtn = (ImageButton) brushDialog.findViewById(R.id.large_brush);
largeBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
drawView.setErase(true);
drawView.setBrushSize(largeBrush);
brushDialog.dismiss();
}
});
brushDialog.show();
} else if (view.getId() == R.id.new_btn) {
//new button
AlertDialog.Builder newDialog = new AlertDialog.Builder(this);
newDialog.setTitle("New drawing");
newDialog.setMessage("Start new drawing (you will lose the current drawing)?");
newDialog.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
drawView.startNew();
dialog.dismiss();
}
});
newDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
newDialog.show();
} else if (view.getId() == R.id.save_btn) {
//save drawing
AlertDialog.Builder saveDialog = new AlertDialog.Builder(this);
saveDialog.setTitle("Save drawing");
saveDialog.setMessage("Save drawing to device Gallery?");
saveDialog.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
//save drawing
drawView.setDrawingCacheEnabled(true);
//attempt to save
String imgSaved = MediaStore.Images.Media.insertImage(
getContentResolver(), drawView.getDrawingCache(),
UUID.randomUUID().toString() + ".png", "drawing");
//feedback
if (imgSaved != null) {
Toast savedToast = Toast.makeText(getApplicationContext(),
"Drawing saved to Gallery!", Toast.LENGTH_SHORT);
savedToast.show();
} else {
Toast unsavedToast = Toast.makeText(getApplicationContext(),
"Oops! Image could not be saved.", Toast.LENGTH_SHORT);
unsavedToast.show();
}
drawView.destroyDrawingCache();
}
});
saveDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
saveDialog.show();
}
/* else if (view.getId() == R.id.btnUndo) {
//undo drawing
{
//drawView.setErase(true);
drawView.undo();
/* if (paths.size() > 0) {
// drawView.setErase(true);
undonePaths.add(paths.remove(paths.size() - 1));
view.invalidate();
} else {
Toast.makeText(getBaseContext(), "undo isnt working", Toast.LENGTH_SHORT).show();
}*/
else if (view.getId() == R.id.opacity_btn) {
//launch opacity chooser
final Dialog seekDialog = new Dialog(this);
seekDialog.setTitle("Opacity level:");
seekDialog.setContentView(R.layout.opacity_chooser);
//get ui elements
final TextView seekTxt = (TextView) seekDialog.findViewById(R.id.opq_txt);
final SeekBar seekOpq = (SeekBar) seekDialog.findViewById(R.id.opacity_seek);
//set max
seekOpq.setMax(100);
//show current level
int currLevel = drawView.getPaintAlpha();
seekTxt.setText(currLevel + "%");
seekOpq.setProgress(currLevel);
//update as user interacts
seekOpq.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
@Override
public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
seekTxt.setText(Integer.toString(progress) + "%");
}
@Override
public void onStartTrackingTouch(SeekBar seekBar) {
}
@Override
public void onStopTrackingTouch(SeekBar seekBar) {
}
});
//listen for clicks on ok
Button opqBtn = (Button) seekDialog.findViewById(R.id.opq_ok);
opqBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
drawView.setPaintAlpha(seekOpq.getProgress());
seekDialog.dismiss();
}
});
//show dialog
seekDialog.show();
}
}
}
DrawingView.java：
（撤銷功能是在這個類的底部）
public class DrawingView extends View{
private ArrayList<Path> paths = new ArrayList<Path>();
private ArrayList<Path> undonePaths = new ArrayList<Path>();
private Path drawPath;
//drawing and canvas paint
private Paint drawPaint, canvasPaint;
//initial color
private int paintColor = 0xFF660000, paintAlpha = 255;
//canvas
private Canvas drawCanvas;
//canvas bitmap
private Bitmap canvasBitmap;
//brush sizes
private float brushSize, lastBrushSize;
//erase flag
private boolean erase = false;
public DrawingView(Context context, AttributeSet attrs) {
super(context, attrs);
setupDrawing();
}
private void setupDrawing() {
brushSize = getResources().getInteger(R.integer.medium_size);
lastBrushSize = brushSize;
drawPath = new Path();
drawPaint = new Paint();
drawPaint.setColor(paintColor);
drawPaint.setAntiAlias(true);
drawPaint.setStrokeWidth(brushSize);
drawPaint.setStyle(Paint.Style.STROKE);
drawPaint.setStrokeJoin(Paint.Join.ROUND);
drawPaint.setStrokeCap(Paint.Cap.ROUND);
canvasPaint = new Paint(Paint.DITHER_FLAG);
// paths.add(drawPath);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
canvasBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
drawCanvas = new Canvas(canvasBitmap);
}
//draw the view - will be called after touch event
@Override
protected void onDraw(Canvas canvas) {
for (Path path : paths) {
canvas.drawPath(path, drawPaint);
}
canvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint);
canvas.drawPath(drawPath, drawPaint);
}
//register user touches as drawing action
@Override
public boolean onTouchEvent(MotionEvent event) {
float touchX = event.getX();
float touchY = event.getY();
//respond to down, move and up events
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
drawPath.moveTo(touchX, touchY);
break;
case MotionEvent.ACTION_MOVE:
drawPath.lineTo(touchX, touchY);
break;
case MotionEvent.ACTION_UP:
drawPath.lineTo(touchX, touchY);
drawCanvas.drawPath(drawPath, drawPaint);
drawPath.reset();
break;
default:
return false;
}
//redraw
invalidate();
return true;
}
//update color
public void setColor(String newColor) {
invalidate();
//check whether color value or pattern name
if (newColor.startsWith("#")) {
paintColor = Color.parseColor(newColor);
drawPaint.setColor(paintColor);
drawPaint.setShader(null);
} else {
//pattern
int patternID = getResources().getIdentifier(
newColor, "drawable", "com.example.drawingfun");
//decode
Bitmap patternBMP = BitmapFactory.decodeResource(getResources(), patternID);
//create shader
BitmapShader patternBMPshader = new BitmapShader(patternBMP,
Shader.TileMode.REPEAT, Shader.TileMode.REPEAT);
//color and shader
drawPaint.setColor(0xFFFFFFFF);
drawPaint.setShader(patternBMPshader);
}
}
//set brush size
public void setBrushSize(float newSize) {
float pixelAmount = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,
newSize, getResources().getDisplayMetrics());
brushSize = pixelAmount;
drawPaint.setStrokeWidth(brushSize);
}
//get and set last brush size
public void setLastBrushSize(float lastSize) {
lastBrushSize = lastSize;
}
public float getLastBrushSize() {
return lastBrushSize;
}
//set erase true or false
public void setErase(boolean isErase) {
erase = isErase;
if (erase) drawPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
else drawPaint.setXfermode(null);
}
//start new drawing
public void startNew() {
drawCanvas.drawColor(0, PorterDuff.Mode.CLEAR);
invalidate();
}
//return current alpha
public int getPaintAlpha() {
return Math.round((float) paintAlpha/255 * 100);
}
//set alpha
public void setPaintAlpha(int newAlpha) {
paintAlpha = Math.round((float) newAlpha/100 * 255);
drawPaint.setColor(paintColor);
drawPaint.setAlpha(paintAlpha);
}
//define undo func
public void undo() {
if (paths.size() > 0) {
undonePaths.add(paths.remove(paths.size() - 1));
invalidate();
} else {
Toast.makeText(getContext(), "undo isnt working wth", Toast.LENGTH_SHORT).show();
}
}
}
prolly因爲你沒有做什麼很明顯像在創建新的路徑，並把它放入數組「上下來「...在」繪製「你應該顯然從這個數組中繪製所有路徑 – Selvin