>我正在尝试创建一个简单的绘图应用程序，允许您在画布上绘图，并且您可以更改它的颜色和厚度。正在发生的问题是，每次我尝试更改油漆的颜色或厚度时，它都会更改画布上已经存在的油漆。我明白为什么它不起作用，但我只是不知道如何解决它以及问题到底在哪里。
画布视图类
package samkough.com.painter;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.view.MotionEvent;
import android.view.View;
import java.util.ArrayList;
public class CanvasView extends View
{
/*
* When the user touches the screen and moves their finger to draw,
* we will use a Path to trace their drawing action on the canvas.
* Both the canvas and the drawing on top of it are represented by Paint
* objects. The initial paint color corresponds to the first color
* in the palette we created last time, which will be initially selected
* when the app launches. Finally we declare variables for the canvas
* and bitmap - the user paths drawn with drawPaint will be drawn onto
* the canvas, which is drawn with canvasPaint.
* */
//drawing paint
private Paint paint = new Paint();
// canvas paint
private Paint canvasPaint = new Paint();
//drawing path
private Path path = new Path();
// canvas
private Canvas canvas = new Canvas();
//canvas bitmap
private Bitmap canvasBitmap;
// brush size and pixel size
private float brushSize, pixelAmount;
public CanvasView(Context context, AttributeSet attrs)
{
// Setting the anti-alias, stroke join and cap styles will make the user's drawings appear smoother.
super(context, attrs);
paint.setAntiAlias(true);
paint.setStrokeWidth(5);
paint.setColor(Color.BLACK);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeJoin(Paint.Join.ROUND);
paint.setStrokeCap(Paint.Cap.ROUND);
}
@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);
canvas = new Canvas(canvasBitmap);
}
@Override
protected void onDraw(Canvas drawCanvas)
{
drawCanvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint);
drawCanvas.drawPath(path, paint);
}
@Override
public boolean onTouchEvent(MotionEvent e)
{
// get the coords of the touch event
float eventX = e.getX();
float eventY = e.getY();
switch (e.getAction()) {
case MotionEvent.ACTION_DOWN:
// set a new starting point
path.moveTo(eventX, eventY);
path.reset();
path.moveTo(eventX, eventY);
return true;
case MotionEvent.ACTION_MOVE:
// connect the points
path.lineTo(eventX, eventY);
break;
default:
return false;
}
// makes you view repaint and call ondraw
invalidate();
return true;
}
public void clearCanvas()
{
path.reset();
invalidate();
}
public void setStrokeWidth(float f)
{
pixelAmount = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, f, getResources().getDisplayMetrics());
brushSize = pixelAmount;
paint.setAntiAlias(true);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeJoin(Paint.Join.ROUND);
paint.setStrokeCap(Paint.Cap.ROUND);
paint.setStrokeWidth(brushSize);
invalidate();
}
public void setColor(int p)
{
paint.setAntiAlias(true);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeJoin(Paint.Join.ROUND);
paint.setStrokeCap(Paint.Cap.ROUND);
paint.setColor(p);
invalidate();
}
}
主活动类
package samkough.com.painter;
import android.app.Activity;
import android.content.Intent;
import android.graphics.Color;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.ImageButton;
import com.samkough.painter.R;
public class MainActivity extends Activity {
private CanvasView canvasView;
private int orange;
private int purple;
private float strokeWidth;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
canvasView = (CanvasView) findViewById(R.id.canvasView);
orange = Color.rgb(250, 128, 0);
purple = Color.rgb(128, 0, 128);
strokeWidth = 0;
// REGULAR BUTTONS: save, about, reset
Button saveB = (Button) findViewById(R.id.saveButton);
Button aboutB = (Button) findViewById(R.id.aboutButton);
Button resetB = (Button) findViewById(R.id.resetButton);
// IMAGE BUTTONS: red, blue, green, yellow, black, purple, orange, erase, brush thickness plus, brush thickness minus
ImageButton redIb = (ImageButton) findViewById(R.id.redButton);
ImageButton blueIb = (ImageButton) findViewById(R.id.blueButton);
ImageButton greenIb = (ImageButton) findViewById(R.id.greenButton);
ImageButton yellowIb = (ImageButton) findViewById(R.id.yellowButton);
ImageButton blackIb = (ImageButton) findViewById(R.id.blackButton);
ImageButton purpleIb = (ImageButton) findViewById(R.id.purpleButton);
ImageButton orangeIb = (ImageButton) findViewById(R.id.orangeButton);
ImageButton eraseIb = (ImageButton) findViewById(R.id.eraseButton);
ImageButton plusIb = (ImageButton) findViewById(R.id.plusButton);
ImageButton minusIb = (ImageButton) findViewById(R.id.minusButton);
minusIb.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v)
{
strokeWidth -= 2;
canvasView.setStrokeWidth(strokeWidth);
}
});
plusIb.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
strokeWidth += 2;
canvasView.setStrokeWidth(strokeWidth);
}
});
eraseIb.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
canvasView.setColor(Color.TRANSPARENT);
}
});
orangeIb.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
canvasView.setColor(orange);
}
});
purpleIb.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
canvasView.setColor(purple);
}
});
blackIb.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
canvasView.setColor(Color.BLACK);
}
});
yellowIb.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
canvasView.setColor(Color.YELLOW);
}
});
greenIb.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
canvasView.setColor(Color.GREEN);
}
});
blueIb.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
canvasView.setColor(Color.BLUE);
}
});
redIb.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
canvasView.setColor(Color.RED);
}
});
saveB.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
}
});
aboutB.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(getApplicationContext(), AboutActivity.class);
startActivity(intent);
}
});
resetB.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
canvasView.clearCanvas();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
你已经创建了canvas，但你没有使用它来绘制任何东西。所以从本质上讲，这条线drawCanvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint);什么都不做。
相反，您需要做的是在canvas上绘制path。然后使用 drawCanvas 绘制canvasBitmap。这样，您可以维护单个path和单个paint，而不是多个。
@Override
protected void onDraw(Canvas drawCanvas)
{
canvas.drawPath(path, paint);
drawCanvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint);
}
当您执行上述操作时，每次用户绘制新路径时，canvasBitmap都将保留其中的所有旧路径。因此，每次调用onDraw时，仅绘制新的path。
永远记住：创建多个 PAINT 对象是一种不好的做法。尝试尽可能重用Paint对象。
在CanvasView.java中，这一行
private Paint paint = new Paint();
为整个类声明一个 paint 对象，并且此行
private Path path = new Path();
为整个类声明一个 Path 对象。
调用 onDraw 时，将重新绘制整个画布区域。 这意味着
drawCanvas.drawPath(path, paint);
绘制自创建活动以来添加的整个path，无论当前值paint是什么。
解决此问题的一种方法是具有Path对象列表和Paint对象列表。 路径列表的第一个元素将存储绘制的第一个路径 - 例如，绘制的所有内容，直到它们更改油漆为止。 油漆列表的第一个元素将存储使用的相应油漆。 每当用户更改油漆并开始绘制时，都需要创建一个新的Path对象，并将其和新的Paint对象添加到列表中。
一旦你有了路径和绘制它们的油漆的列表，你可以在onDraw中做这样的事情：
for (int i = 0; i < paths.size(); i++) {
Path path = paths.get(i);
Paint paint = paints.get(i);
drawCanvas.drawPath(path, paint);
}