如何给Android中的按钮添加图片功能

<?xml version="1.0" encoding="utf-8"?>
<linearlayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:gravity="center"
    android:background="@drawable/app_icon"
    android:orientation="vertical" >
    <button
      android:id="@+id/startorder_btn"
      android:layout_width="fill_parent"
      android:layout_height="fill_parent"
      android:background="@drawable/apply"
      android:textsize="25sp" >
    </button>
    <button
      android:id="@+id/managerorder_btn"
      android:layout_width="fill_parent"
      android:layout_height="fill_parent"
      android:background="@drawable/apply"
      android:textsize="25sp" >
    </button>
</linearlayout>
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在drawable-xxhdpi中添加图片
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layoutinflater inflater = layoutinflater.from(mmainactivity);
  view layout=inflater.inflate(r.layout.my_login,null);
  contextthemewrapper contextthemewrapper = new contextthemewrapper(mainactivity.this, 2131099656);
  alertdialog.builder builder =new alertdialog.builder(contextthemewrapper);
  builder.setview(layout);
  builder.setcancelable(false);
  builder.create().show();
  button startorder_btn=(button) layout.findviewbyid(r.id.startorder_btn);
  button managerorder_btn=(button) layout.findviewbyid(r.id.managerorder_btn);
  startorder_btn.setonclicklistener(new onclicklistener(){
  public void onclick(view v) {
  //加上你要实现的代码
  ysdkapi.login(eplatform.qq);
  }
  });
  managerorder_btn.setonclicklistener(new onclicklistener(){
  public void onclick(view v) {//加上你要实现的代码
  ysdkapi.login(eplatform.wx);
  }
  });