保证金的扭曲图像大小

Question

当我设置此ImageButton的边距时，它会扭曲图像的大小。为什么会这样？

代码：

package com.example.e99900004533.candycollector;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.graphics.Point;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.Display;
import android.view.ViewGroup.MarginLayoutParams;
import android.widget.LinearLayout;
import android.view.ViewGroup.LayoutParams;
import android.widget.RelativeLayout;
import android.widget.EditText;
import android.widget.ImageButton;
import java.util.Random;

public class MainActivity extends ActionBarActivity {

    public EditText collectedTextEdit;
    public ImageButton candyEdit;
    public int collected = 0;
    public int screenWidth = 300;
    public int screenHeight = 300;
    Random random = new Random();
    public boolean running = true;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        collectedTextEdit = (EditText) findViewById(R.id.collectedText);
        candyEdit = (ImageButton) findViewById(R.id.candy);
        collectedTextEdit.setText("Collected: " + collected);

        Display display = getWindowManager().getDefaultDisplay();
        Point size = new Point();
        display.getSize(size);
        screenWidth = size.x;
        screenHeight = size.y;

        addListenerOnButton();
    }

    public void addListenerOnButton() {
        candyEdit.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                collected += 1;
                collectedTextEdit.setText("Collected: " + collected);

                int candyX = random.nextInt(screenWidth - 50);
                int candyY = random.nextInt(screenHeight - 50);
                System.out.println(candyX + " : " + candyY);

                MarginLayoutParams marginParams = new MarginLayoutParams(candyEdit.getLayoutParams());
                marginParams.setMargins(candyX, candyY,  LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
                RelativeLayout.LayoutParams layoutParams = new RelativeLayout.LayoutParams(marginParams);
                candyEdit.setLayoutParams(layoutParams);

                if (candyX > screenWidth) {
                    screenWidth -= 50;
                    layoutParams.setMargins(candyX, candyY, LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
                    candyEdit.setLayoutParams(layoutParams);
                }
                if (candyY > screenHeight) {
                    screenHeight -= 50;
                    layoutParams.setMargins(candyX, candyY, LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
                    candyEdit.setLayoutParams(layoutParams);
                }

                //while (running == true) {
                    //candyY -= 1;
                    //layoutParams.setMargins(candyX, candyY, candyX, candyY);
                    //candyEdit.setLayoutParams(layoutParams);
                //}
            }
        });
    }

    @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);
    }
}

这是ImageButton代码：

<ImageButton
    android:layout_width="50dp"
    android:layout_height="50dp"
    android:id="@+id/candy"
    android:background="@drawable/candy"
    android:contentDescription="@string/candyImg"
    android:clickable="true"
    android:layout_below="@+id/collectedText"
    android:layout_alignRight="@+id/collectedText"
    android:layout_alignEnd="@+id/collectedText" />

任何人都可以解释或提供资源，了解设置保证金的确如何运作。 BTW使用Android Api等级15 - 22。 请帮助！