//代碼1： package?com.example.testsdk2; import?android.app.Activity; import?android.content.Intent; import?android.os.Bundle; import?android.view.View; import?android.view.View.OnClickListener; import?android.widget.Button; import?android.widget.Toast; public?class?MainActivity?extends?Activity?{ ????@Override ????protected?void?onCreate(Bundle?savedInstanceState)?{ ????????super.onCreate(savedInstanceState); ????????setContentView(R.layout.activity_main); ????????Button?bu=(Button)findViewById(R.id.bu_1); ????????bu.setOnClickListener(new?OnClickListener()?{ ???????????? ????????????@Override ????????????public?void?onClick(View?v)?{ ????????????????Intent?intent=new?Intent(MainActivity.this,?scActivity.class); ????????????????startActivity(intent); ????????????????Toast.makeText(MainActivity.this,?"按鈕被按下",?Toast.LENGTH_LONG).show(); ???????????????? ????????????} ????????}); ????} ???? }<RelativeLayout?xmlns:android="http://schemas.android.com/apk/res/android" ????xmlns:tools="http://schemas.android.com/tools" ????android:layout_width="match_parent" ????android:layout_height="match_parent" ????android:paddingBottom="@dimen/activity_vertical_margin" ????android:paddingLeft="@dimen/activity_horizontal_margin" ????android:paddingRight="@dimen/activity_horizontal_margin" ????android:paddingTop="@dimen/activity_vertical_margin" ????tools:context="com.example.testsdk2.MainActivity"?> ????<TextView ????????android:id="@+id/tx_1" ????????android:layout_width="wrap_content" ????????android:layout_height="wrap_content" ????????android:text="@string/hello_world"?/> ????<Button? ????????android:id="@+id/bu_1" ????????android:layout_width="wrap_content" ????????android:layout_height="wrap_content" ????????android:text="點擊按鈕進行測試" ????????/> </RelativeLayout>package?com.example.testsdk2; import?android.app.Activity; import?android.graphics.Color; import?android.os.Bundle; import?android.view.View; import?android.view.View.OnClickListener; import?android.widget.Button; import?android.widget.TextView; import?android.widget.Toast; public?class?scActivity?extends?Activity?{ ????@Override ????protected?void?onCreate(Bundle?savedInstanceState)?{ ????????//?TODO?Auto-generated?method?stub ????????super.onCreate(savedInstanceState); ????????setContentView(R.layout.activity_main); ???????? ????} }如果activity.findViewById()方法查找的是對象，那么點擊第一個activity上面的“點擊按鈕進行測試”按鈕切換到scActivity之后，再次點擊該按鈕，會第二次彈出Toast提示信息而且，如果兩個activity布局XML文件不一樣，在其中一個對另一個布局文件中定義的View組件id進行引用并修改屬性會造成程序崩潰。代碼如下：//代碼2： package?com.example.testsdk2; import?android.app.Activity; import?android.graphics.Color; import?android.os.Bundle; import?android.view.View; import?android.view.View.OnClickListener; import?android.widget.Button; import?android.widget.TextView; import?android.widget.Toast; public?class?scActivity?extends?Activity?{ ????@Override ????protected?void?onCreate(Bundle?savedInstanceState)?{ ????????//?TODO?Auto-generated?method?stub ????????super.onCreate(savedInstanceState); ????????setContentView(R.layout.sc_activity); ???????? ????????Button?but=(Button)findViewById(R.id.bu_2); ????????but.setOnClickListener(new?OnClickListener()?{ ???????????? ????????????@Override ????????????public?void?onClick(View?v)?{ ????????????????Toast.makeText(scActivity.this,"點擊修改按鈕",?Toast.LENGTH_LONG).show(); ????????????????Button?bu1=(Button)findViewById(R.id.bu_1); ????????????????Toast.makeText(scActivity.this,"查找id沒崩潰",?Toast.LENGTH_LONG).show(); //????????????????bu1.setTextColor(Color.RED); ????????????} ????????}); ????} }<?xml?version="1.0"?encoding="utf-8"?> <LinearLayout?xmlns:android="http://schemas.android.com/apk/res/android" ????android:layout_width="match_parent" ????android:layout_height="match_parent" ????android:orientation="vertical"?> ???? ????<Button? ???????android:id="@+id/bu_2" ???????android:layout_width="wrap_content" ???????android:layout_height="wrap_content" ???????android:text="點擊啟動修改" ????????/> </LinearLayout>如果activity.findViewById()查找的是id指向的對象，那么為什么代碼1中添加的監聽事件在scActivity中失效，如果查找的不是對象，那返回的是什么？