单击时为按钮着色

Question

I am creating a small calculator for Android. The keyboard of the calculator is created by Java code in OnDraw:

public void onDraw(Canvas canvas){
    buttonH = height/rows;
    Paint paint = new Paint();
    paint.setTextAlign(Paint.Align.CENTER);
    AssetManager assetManager = getResources().getAssets();
        Typeface tf = Typeface.create(Typeface.createFromAsset(assetManager,"fonts/font.ttf"),
    Typeface.NORMAL);

    paint.setTypeface(tf);
    paint.setAntiAlias(true);

    textSize = (width+height)/43;

    paint.setTextSize(textSize);
    paint.setColor(Color.rgb(0, 0, 0));

    Bitmap[][] buttons = new Bitmap[rows][];
    int spacing = (width+height)/400;

    LinearGradient gradient = new LinearGradient(buttonW/2,0,buttonW/2,buttonH,
                buttonShade,null,Shader.TileMode.REPEAT);

    for(int i = 0; i < rows; i++){
        int thisColumns = cScreen[i].length;
        buttons[i] = new Bitmap[thisColumns];
        buttonW = width/thisColumns;
        for(int j = 0; j < thisColumns; j++){

            buttons[i][j] = Bitmap.createBitmap(buttonW,buttonH,Bitmap.Config.ARGB_8888);
            Canvas temp = new Canvas(buttons[i][j]);
            paint.setShader(gradient1);
            RectF rect = new RectF(spacing,spacing,buttonW-spacing,buttonH-spacing);
            temp.drawRoundRect(rect, width/100,height/100,paint);
            paint.setShader(null);
            temp.drawText(cScreen[i][j],buttonW/2,(buttonH+textSize)/2,paint);
            canvas.drawBitmap(buttons[i][j], buttonW*j+shift,buttonH*i, paint);
        }
    }
}

but I would like to color the area of the button when the button is clicked

Answer 1

If you want just to color the button while it is pressed you can implement this using xml.

   <?xml version="1.0" encoding="utf-8"?> 
   <selector xmlns:android="http://schemas.android.com/apk/res/android"> 
      <item android:state_focused="true" android:state_pressed="true" 
            android:drawable="@drawable/bg_clolor_highlight" /> 
      <item android:state_focused="false" android:state_pressed="true" 
            android:drawable="@drawable/bg_clolor_highlight" /> 
      <item android:drawable="@drawable/bg_clolor_normal" /> 
  </selector>

Otherwise you can just call .setBackgroundColor(your_color) on the button.

Answer 2

Create a different Paint object in onDraw for the clicked button:

 Paint p=new Paint(); 
 paint.setColor(Color.RED);

Get the coordinates of the click position on the canvas:

in constructor attach an onTouch listener()

float x,y;

this.setOnTouchListener(new OnTouchListener() {
     @Override
     public boolean onTouch(View arg0, MotionEvent event) {
          x=event.getX();y=event.getY();
     }
});

in onDraw:

    Paint p=new Paint(); 
    paint.setColor(Color.RED);
for(int i = 0; i < rows; i++){
    int thisColumns = cScreen[i].length;
    buttons[i] = new Bitmap[thisColumns];
    buttonW = width/thisColumns;

    for(int j = 0; j < thisColumns; j++){
        Paint tempPaint;
         if(x> buttonW*j+shift&&x< buttonW*j+shift+buttonW&&y>buttonH*i&&y<buttonH*i+buttonH) 
         tempPaint=p;
         else
         tempPaint=paint;
        buttons[i][j] = Bitmap.createBitmap(buttonW,buttonH,Bitmap.Config.ARGB_8888);
        Canvas temp = new Canvas(buttons[i][j]);
        tempPaint.setShader(gradient1);
        RectF rect = new RectF(spacing,spacing,buttonW-spacing,buttonH-spacing);
        temp.drawRoundRect(rect, width/100,height/100,tempPaint);
        tempPaint.setShader(null);
        temp.drawText(cScreen[i][j],buttonW/2,(buttonH+textSize)/2,tempPaint);

        canvas.drawBitmap(buttons[i][j], buttonW*j+shift,buttonH*i, tempPaint);
    }
}