Android应用程序未像在Android Studio中一样显示在设备上

我正在尝试制作一个显示以下图像的程序：

该图像来自Android Studio上“显示”窗口中用于我尝试显示的活动的XML文件。该窗口包括两个片段，尽管现在只有其中一个具有可见元素。

但是，当在android设备上运行程序时，我只有一个空白屏幕，没有任何我一直在片段中编程的可见对象或功能。不过，我仍然在顶部获得该活动的标题。

应该出现的是底部的两个图标（这是来自ToolbarFragment的两个图像按钮），以及一个由DrawingFragment的画布对象占用的空白区域。我还不确定如何绘制画布，但是至少应该出现按钮。

我认为这与XML文件或活动本身有关，因此我在下面提供了它们的代码。您能提供的任何帮助将不胜感激。

DrawingActivity.java

package com.example.chris.drawingtest;

import android.app.Activity;
import android.util.Log;


public class DrawingActivity extends Activity
    implements ToolbarFragment.ToolSelectionListener {

    public void sendNewValue(int newValue) {
        Log.i("Data received from Toolbar Fragment: ", "The ID of the button pressed is " + newValue);
    }
}

activity_drawing.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:layout_gravity="bottom"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".com.example.chris.drawingtest.DrawingActivity">

    <fragment
        android:name="com.example.chris.drawingtest.DrawingFragment"
        android:id="@+id/Drawing"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        tools:layout="@layout/fragment_drawing"
    />

    <fragment
        android:name="com.example.chris.drawingtest.ToolbarFragment"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/Toolbar"
        tools:layout="@layout/fragment_toolbar"
    />

</LinearLayout>

编辑：添加了片段代码。

ToolbarFragment.java

package com.example.chris.drawingtest;

import android.app.Activity;
import android.app.Fragment;
import android.content.DialogInterface;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.ImageButton;

import com.example.chris.drawingtest.R;

/**
 * Created by Chris on 11/28/2014.
 */
public class ToolbarFragment extends Fragment {

    ToolSelectionListener mCallback;

    public interface ToolSelectionListener {
        public void sendNewValue(int newValue);
    }

    public void clicked(ImageButton imageButton) {
        mCallback.sendNewValue(imageButton.getId());
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_toolbar, container, false);
    }

    private ImageButton pencilButton = (ImageButton) getActivity().findViewById(R.id.pencil);
    private ImageButton eraserButton = (ImageButton) getActivity().findViewById(R.id.eraser);


}

DrawingFragment.java

package com.example.chris.drawingtest;

import android.app.Activity;
import android.app.Fragment;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Path;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageButton;
import android.widget.LinearLayout;

import com.example.chris.drawingtest.R;

/**
 * Created by Chris on 11/28/2014.
 */
public class DrawingFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_drawing, container, false);
    }

    private class DrawView extends View {

        private Path drawpath = new Path();
        private Paint drawpaint = new Paint();
        private Paint canvaspaint;
        private Canvas drawcanvas;
        private Bitmap canvasBitmap;

        private int paintColor = 0xFF000000;    //opaque black for pencil

        public DrawView(Context context) {
            super(context);
            drawpaint.setColor(paintColor);

            drawpaint.setStrokeWidth(10);
            drawpaint.setStyle(Paint.Style.STROKE);
            drawpaint.setStrokeJoin(Paint.Join.ROUND);
            drawpaint.setStrokeCap(Paint.Cap.ROUND);

            canvaspaint = new Paint(Paint.DITHER_FLAG);
        }

        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);
            drawcanvas = new Canvas(canvasBitmap);
        }

        @Override
        protected void onDraw(Canvas canvas) {
            super.onDraw(canvas);

            drawcanvas.drawBitmap(canvasBitmap,0,0,drawpaint);
            canvas.drawPath(drawpath, drawpaint);
        }

        @Override
        public boolean onTouchEvent(MotionEvent event) {
            float touchX = event.getX();
            float touchY = event.getY();

            switch(event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    drawpath.moveTo(touchX,touchY);
                    break;
                case MotionEvent.ACTION_MOVE:
                    drawpath.lineTo(touchX,touchY);
                    break;
                case MotionEvent.ACTION_UP:
                    drawcanvas.drawPath(drawpath, drawpaint);
                    drawpath.reset();
                    break;
                default:
                    return false;
            }
            invalidate();
            return true;
        }

    }

   Integer value = 0;

}