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Android开发：findViewById返回null的解决办法
来源：Linux社区&
作者：pathuang68
在用Eclipse进行的界面开发，通过findViewById试图获取界面元素对象时，该方法有时候返回null，造成这种情况主要有以下两种情形。
第一种情形是最普通的。比如main.xml如下，其中有一个ListView，其id为lv_contactbook
&?xml version="1.0"encoding="utf-8"?&
&LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
&&& android:orientation="vertical"
&&& android:layout_width="fill_parent"
&&& android:layout_height="fill_parent"
&&& &EditText android:id="@+id/et_search"
&&& android:layout_width="fill_parent"
&&& android:layout_height="wrap_content"
&&& android:text=""
&&&&&&&& &ListView android:id="@+id/lv_contactbook"
&&&&&&&&&&&&&&&&&& android:layout_width="fill_parent"
&&&&&&&&&&&&&&&&&& android:layout_height="wrap_content"
&&&&&&&& /&
&/LinearLayout&
如果在Activity对应的代码中，是这样的写的：
public void onCreate(BundlesavedInstanceState)
&&&&&&&& super.onCreate(savedInstanceState);
&&&&&&&& ListViewlv = (ListView)findViewById(R.id.lv_contactbook);
&&&&&&&& setContentView(R.layout.main);
&&&&&&&& //…
即在setContentView调用之前，调用了findViewById去找main布局中的界面元素lv_contactbook，那么所得到的lv一定是null。正确的做法是将上面代码中加粗的哪一行，挪至setContentView方法调用之后。
第二种情形。这种情况下通常是调用LayoutInflater.inflate将布局xml规定的内容转化为相应的对象。比如有rowview.xml布局文件如下(比如在自定义Adapter的时候，用作ListView中的一行的内容的布局)：
&?xml version="1.0"encoding="utf-8"?&
&LinearLayout
& xmlns:android="http://schemas.android.com/apk/res/android"
& android:orientation="horizontal"
& android:layout_width="fill_parent"
& android:layout_height="wrap_content"
&TextView android:id="@+id/tv_contact_id"
&&&&&&&& &&& &android:layout_width="0px"
&&&&&&&& &&& &android:layout_height="0px"
&&&&&&&& &&& &android:visibility="invisible"
&&&&&&&& &&& &android:gravity="center_vertical"
&TextView android:id="@+id/tv_contactname"
&&&&&&&& &&& android:layout_width="wrap_content"
&&&&&&&& &&& android:layout_height="36dip"
&&&&&&&& &&& android:textSize="16dip"
&&&&&&&& &&& android:layout_marginTop="10dip"
&&&&&&&& &&& android:textColor="#FFFFFFFF"
&/LinearLayout&
假定在自定的Adapter的getView方法中有类似如下的代码：
View rowview = (View)inflater.inflate(R.layout.rowview, parent, false);
TextView tv_contact_id =(TextView)rowview.findViewById(R.id.tv_contact_id);
TextView tv_contactname =(TextView)rowview.findViewById(R.id.tv_contactname);
有时候居然也会发现rowview非空，但tv_contact_id和tv_contactname都是null！仔细看代码，怎么也看不出错误来。到底是什么原因造成的呢？答案是Eclipse造成的，要解决这个问题，需要这个项目clean一次(Project菜单 -& Clean子菜单)，这样就OK了。&
第二种情况很隐蔽，因为代码的确没有错。如果一时没有想到解决办法会浪费很多时间。
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匿名 发表于 多谢android新手开发，eclipse环境SDK用的是4.1的， mybutton = (Button)findViewById(R.id.mybutton);_百度知道
android新手开发，eclipse环境SDK用的是4.1的， mybutton = (Button)findViewById(R.id.mybutton);
ndroid新手开发，eclipse环境SDK用的是4.1的，报错错误，button的包已经导入了
Description Resource Path Location Type
Call requires API level 11 (current min is 8): android.app.ActionBar#setDisplayHomeAsUpEnabled Activity_02.java /Activity_02/s...
原因就是api版本低修改的步骤：第一步：修改AndroidManifest.xml里的&uses-sdk android:minSdkVersion=&11& /&第二步：修改project.properties文件里的target=android-11第三步：右键工程--&Android Tools--&Fix project properties完毕
采纳率：39%
你选择的api版本不对。你那个句子是api11才有的 而你选择的是api8
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processed in 0.055 (s). 11 q(s)eclipse找不得listview控件 在java文件里用findviewbyid 方法绑定_百度知道
eclipse找不得listview控件 在java文件里用findviewbyid 方法绑定
了listview
我有更好的答案
1.首先你要确认你的R文件是否是正确的。findviewbyid 方法绑定出现错误，通常都是R文件的错误导致的！查看R引用的是否是当前项目的R文件。2.如果是直接就找不到ListView控件，那可能是你的Sdk包的问题！请检查你的sdk关联是否正确，下载的包是否完整！
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