java - 如何在android studio中更改按钮的高度和宽度以及通过drawable canvas添加按钮？

Question

我在android studio中制作了蛇梯游戏。我想更改按钮的高度和宽度，并且我想再添加一个退出按钮。现在我只对所有按钮使用一个 .png 文件。那么，如何改变呢？当我添加第四个按钮时，我的应用程序崩溃并显示错误。 Check this image

错误

    FATAL EXCEPTION: main
    Process: com.sixtinbyte.snakeandladder, PID: 25115
 java.lang.NullPointerException: Attempt to invoke virtual method 'void com.sixtinbyte.snakeandladder.components.GameButton.onDraw(android.graphics.Canvas)' on a null object reference
 at com.sixtinbyte.snakeandladder.HomeView.onDraw(HomeView.java:151)

主页 View 。 java(这是我想要更改的java文件，因为这是游戏的主屏幕)

import android.content.Context;
import android.content.Intent;
import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Point;
import android.graphics.drawable.Drawable;
import android.view.MotionEvent;
import android.view.View;

import com.sixtinbyte.snakeandladder.components.GameButton;
import com.sixtinbyte.snakeandladder.constant.Sound;


public class HomeView extends View {
 public Context ctx;
 private Resources res;
 private String refText ="Snakes and Ladders";
 private GameButton gButton, sButton, hButton,eButton;
 private Bitmap logo, play, settings, help, exit;
    private int hWidth, hHeight;
 private Point touchCoordinate = new Point();


 public HomeView(Context ctx) {
    super(ctx);
    this.ctx = ctx;
    res = getResources();
    logo = BitmapFactory.decodeResource(res, R.drawable.snakes_n_ladders);

 }

 @Override
 protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    // TODO: Implement this method
    super.onSizeChanged(w, h, oldw, oldh);
    hWidth = w;
    hHeight = h;
    preparePlayButton();
    prepareSettingsButton();
    prepareHelpButton();
//   prepareExitButton();
 }

    private void preparePlayButton() {
    String text =" ";
    int textSize = 40;
    Point po = getBmpMeasureFrom(text, refText, textSize);
    play = getBitmap(R.drawable.play, po.x, po.y);
    gButton = new GameButton(play, text, textSize);
    gButton.setLocation((hWidth - po.x) / 2, (int)(hHeight * 0.6f));
    gButton.setTextColor(Color.CYAN);
 }
 private void prepareSettingsButton() {
    String text =" ";
    int textSize = 40;
    Point po = getBmpMeasureFrom(text, refText, textSize);
    settings = getBitmap(R.drawable.play, po.x, po.y);
    sButton = new GameButton(settings, text, textSize);
    sButton.setLocation((hWidth - po.x) / 2, (int)(hHeight * 0.7f));
    sButton.setTextColor(Color.CYAN);
 }
//
//
 private void prepareHelpButton() {
    String text =" ";
    int textSize = 40;
    Point po = getBmpMeasureFrom(text, refText, textSize);
    help = getBitmap(R.drawable.play, po.x, po.y);
    hButton = new GameButton(help, text, textSize);
    hButton.setLocation((hWidth - po.x) / 2, (int)(hHeight * 0.8f));
    hButton.setTextColor(Color.CYAN);
 }
//  private void prepareExitButton() {
//      String text =" ";
//      int textSize = 40;
//      Point po = getBmpMeasureFrom(text, refText, textSize);
//      help = getBitmap(R.drawable.play, po.x, po.y);
//      hButton = new GameButton(help, text, textSize);
//      hButton.setLocation((hWidth - po.x) / 2, (int)(hHeight * 0.8f));
//      hButton.setTextColor(Color.CYAN);
//
//  }

 private Point getBmpMeasureFrom(String text, String refText, int textSize) {
    Point p = new Point();
    Paint pa = new Paint();
    pa.setTextSize(textSize);
    p.y = (int)(pa.getTextSize() * 2.2f);
    String tt = refText.length() > text.length() ?refText: text;
    p.x = (int) (pa.measureText(tt) * 1.2f);
    return p;
 }

 @Override
 public boolean onTouchEvent(MotionEvent event) {
    // TODO: Implement this method
    int evt = event.getAction();
    touchCoordinate.x = (int)event.getX();
    touchCoordinate.y = (int)event.getY();
    switch (evt) {
     case MotionEvent.ACTION_DOWN:
 MainActivity.playSound(Sound.BUTTON_CLICK_1, false);
        break;
     case MotionEvent.ACTION_MOVE:

        break;
     case MotionEvent.ACTION_UP:
//      MainActivity.stopSound();
        if (gButton.contains(touchCoordinate)) {
         Intent intent = new Intent(ctx, GameActivity.class);
         ctx. startActivity(intent);
        }
        if (sButton.contains(touchCoordinate)) {

         Intent intent = new Intent(ctx, Playing.class);
            ctx.startActivity(intent);
        }
        if (hButton.contains(touchCoordinate)) {

         Intent intent = new Intent(ctx, Aboutus.class);
         ctx. startActivity(intent);
        }
//       if(eButton.contains(touchCoordinate)){
//           Intent intent = new Intent(ctx, Exit.class);
//           ctx.startActivity(intent);
//       }

        break;
    }
    return true;
 }



 @Override
 protected void onDraw(Canvas canvas) {
    // TODO: Implement this method
    super.onDraw(canvas);
    canvas.drawColor(Color.CYAN);

    canvas.drawBitmap(logo, (hWidth - logo.getWidth()) / 2, (int)((hHeight - logo.getHeight()) * 0.1), null);
    gButton.onDraw(canvas);
    sButton.onDraw(canvas);
    hButton.onDraw(canvas);
//  eButton.onDraw(canvas);
//  Paint p= new Paint();
//  p.setColor(Color.RED);
//  canvas.drawRect(100, 200, 400, 500, p);
    invalidate();
 }

 private Bitmap getBitmap(int drawableRes, int width, int height) {
    Drawable d = res.getDrawable(drawableRes);
    Canvas c = new Canvas();
    Bitmap b = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
    c.setBitmap(b);
    d.setBounds(0, 0,width, height);
    d.draw(c);
    return b;
 }

}

Answer 1

prepareExitButton方法正在分配hButton，我认为它应该分配eButton。这就是为什么你会在那里得到 NullPointerException 的原因。另外，您将 y 坐标设置为 (int)(hHeight * 0.8f))，这意味着它将与帮助按钮重叠。

您可能需要更改 GameButton 类才能调整按钮的大小。特别是，您需要更改 onDraw 以按指定大小绘制按钮。