Java 如何在Android中更改画布上绘画的颜色/厚度？

当我点击一个imageButton时，我无法改变油漆的颜色或厚度，即使我也对它进行了编程。我知道我做错了什么，我想我知道为什么，但我无法修复它。我觉得我找对了画笔。以下是我的Java类代码：

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.graphics.PorterDuff;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class CanvasView extends View
{
private Paint paint = new Paint();
private Path path = new Path();
private Canvas canvas = new Canvas();
private Paint canvasPaint = new Paint();
private Bitmap canvasBitmap;

public CanvasView(Context context, AttributeSet attrs)
{
    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);
            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()
{
    canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);
}

这是我的主要活动代码：

public class MainActivity extends Activity {

private CanvasView canvasView;
private Paint paint;
private int orange;
private int purple;

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

    canvasView = (CanvasView) findViewById(R.id.canvasView);
    paint = new Paint();
    orange = Color.rgb(255, 245, 238);
    purple = Color.rgb(128, 0, 128);

    // 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) {
            paint.setStrokeWidth(-5);
        }
    });

    plusIb.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            paint.setStrokeWidth(5);
        }
    });

    eraseIb.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            paint.setColor(Color.TRANSPARENT);
        }
    });

    orangeIb.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            paint.setColor(orange);
        }
    });

    purpleIb.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            paint.setColor(purple);
        }
    });

    blackIb.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            paint.setColor(Color.BLACK);
        }
    });

    yellowIb.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            paint.setColor(Color.YELLOW);
        }
    });

    greenIb.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            paint.setColor(Color.GREEN);
        }
    });

    blueIb.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            paint.setColor(Color.BLUE);
        }
    });

    redIb.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            paint.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();
            // canvasView.clearCanvas2();
        }
    });
}

---

您正在一个与画布视图没有连接的完全不同的绘画上设置值。您必须更改画布视图的绘制，并在其上调用invalidate进行任何更改

在画布视图中执行类似的操作以更改笔划宽度：

public void setStrokeWidth(int strokeWidth) {
    paint.setStrokeWidth(strokeWidth);
    invalidate();
}

并使用

canvasView.setStrokeWidth（5）在
onClick（）中调用它

颜色也是如此：

public void setColor(int color) {
    paint.setColor(color);
    invalidate();
}

并在
onClick（）中使用
canvasView.setColor（Color.BLUE）调用它
如果要在Kotlin中实现

paint.strokeWidth = 3.0f

它可以工作，但是，它有一个bug。它确实会改变颜色，但当它改变时，它也会改变已经存在的图形，因此它不能完全按照预期的方式工作。为了更改画布视图，您必须使其无效，从而重新绘制整个视图。您可以检查更改并仅在
onDraw（）中绘制需要更新的部分，或者使用
invalidate（左、上、右、下）
仅使视图的一部分无效。笔划宽度应大于0，以dp而不是px为单位。传递0将绘制单个像素线。