java - 每次我尝试更改绘画的属性(厚度或颜色)时，它都会更改 Canvas 上已有的现有绘画(android)(java)

Question

我正在尝试创建一个简单的绘图应用程序，让您可以在 Canvas 上绘图，并且可以更改 Canvas 的颜色和粗细。出现的问题是，每次我尝试更改油漆的颜色或厚度时，它都会更改 Canvas 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出在哪里。

CanvasView 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();
    }
}

主要 Activity 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);
    }
}

Answer 1

您已经创建了 canvas，但是您没有使用它在上面绘制任何东西。所以本质上，行 drawCanvas.drawBitmap(canvasBitmap, 0, 0, canvasPaint); 没有做任何事情。

您需要做的是在 canvas 上绘制 path。然后使用 drawCanvas 绘制 canvasBitmap。这样您就可以维护单个 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 都会在其中保存所有旧路径。所以每次调用 onDraw 时，只会绘制新的 path。

永远记住:创建多个PAINT 对象 是一种不好的做法。尽量重用 Paint 对象。