【发布时间】：2015-01-30 02:00:09
【问题描述】：
我有一个如下所示的 android 布局：
内容Bit pattern -->
aaa
在运行时更改为多行字符串，这会导致Send 命令按钮向下移动。为了使按钮保持在同一位置，我将组件的位置更改为如下所示：
在这两种情况下，xml 文件内容似乎相同（如果有区别，则使用 LinearLayout）
<?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:gravity="clip_horizontal"
android:orientation="vertical" >
<TextView
android:id="@+id/freqIndxTextView_id"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/freqIndxTextView_string" />
<TextView
android:id="@+id/freqIndxValTextView_id"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/freqIndxValTextView_string" />
<SeekBar
android:id="@+id/freqIndxSeekBar_id"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp" />
<TextView
android:id="@+id/gainLevelTextView_id"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/gainLevelTextView_string" />
<TextView
android:id="@+id/gainLevelValTextView_id"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/gainLevelValTextView_string" />
<SeekBar
android:id="@+id/gainLevelSeekBar_id"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginLeft="20dp" />
<Button
android:id="@+id/btnInSituActivitySend_id"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="InSituActivitySend_click"
android:text="@string/btnInSituActivitySend_string" />
<TextView
android:id="@+id/bitPatternTextView_id"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/bitPatternTextView_string" />
<TextView
android:id="@+id/bitPatternValTextView_id"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/bitPatternValTextView_string" />
</LinearLayout>
但是在第二种情况下，当这个活动开始时，我得到一个错误并且应用程序关闭：
01-30 10:38:43.351: E/AndroidRuntime(3097): FATAL EXCEPTION: main
01-30 10:38:43.351: E/AndroidRuntime(3097): Process: com.example.fourcommandmenu, PID: 3097
01-30 10:38:43.351: E/AndroidRuntime(3097): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.fourcommandmenu/com.example.fourcommandmenu.InSituActivity}: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.Button
01-30 10:38:43.351: E/AndroidRuntime(3097): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
01-30 10:38:43.351: E/AndroidRuntime(3097): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
01-30 10:38:43.351: E/AndroidRuntime(3097): at android.app.ActivityThread.access$800(ActivityThread.java:135)
01-30 10:38:43.351: E/AndroidRuntime(3097): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
01-30 10:38:43.351: E/AndroidRuntime(3097): at android.os.Handler.dispatchMessage(Handler.java:102)
01-30 10:38:43.351: E/AndroidRuntime(3097): at android.os.Looper.loop(Looper.java:136)
01-30 10:38:43.351: E/AndroidRuntime(3097): at android.app.ActivityThread.main(ActivityThread.java:5001)
01-30 10:38:43.351: E/AndroidRuntime(3097): at java.lang.reflect.Method.invokeNative(Native Method)
01-30 10:38:43.351: E/AndroidRuntime(3097): at java.lang.reflect.Method.invoke(Method.java:515)
01-30 10:38:43.351: E/AndroidRuntime(3097): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
01-30 10:38:43.351: E/AndroidRuntime(3097): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
01-30 10:38:43.351: E/AndroidRuntime(3097): at dalvik.system.NativeStart.main(Native Method)
01-30 10:38:43.351: E/AndroidRuntime(3097): Caused by: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.Button
01-30 10:38:43.351: E/AndroidRuntime(3097): at com.example.fourcommandmenu.InSituActivity.onCreate(InSituActivity.java:70)
01-30 10:38:43.351: E/AndroidRuntime(3097): at android.app.Activity.performCreate(Activity.java:5231)
01-30 10:38:43.351: E/AndroidRuntime(3097): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
01-30 10:38:43.351: E/AndroidRuntime(3097): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2148)
01-30 10:38:43.351: E/AndroidRuntime(3097): ... 11 more
主要错误似乎是这样的：
01-30 10:38:43.351: E/AndroidRuntime(3097): Caused by: java.lang.ClassCastException: android.widget.TextView cannot be cast to android.widget.Button
01-30 10:38:43.351: E/AndroidRuntime(3097): at com.example.fourcommandmenu.InSituActivity.onCreate(InSituActivity.java:70)
onCreate() 中有问题的行是这样的：
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_in_situ);
freqIndxTextView = (TextView)findViewById(R.id.freqIndxTextView_id);
gainLevelTextView = (TextView)findViewById(R.id.gainLevelTextView_id);
freqIndxValTextView = (TextView)findViewById(R.id.freqIndxValTextView_id);
gainLevelValTextView = (TextView)findViewById(R.id.gainLevelValTextView_id);
bitPatternTextView = (TextView)findViewById(R.id.bitPatternTextView_id);
bitPatternValTextView = (TextView)findViewById(R.id.bitPatternValTextView_id);
freqIndxSeekBar = (SeekBar)findViewById(R.id.freqIndxSeekBar_id);
gainLevelSeekBar = (SeekBar)findViewById(R.id.gainLevelSeekBar_id);
btnInSituActivitySend = (Button)findViewById(R.id.btnInSituActivitySend_id);
freqIndxValTextView.setText(Integer.toString(freqIndxSeekBar.getProgress()));
gainLevelValTextView.setText(Integer.toString(gainLevelSeekBar.getProgress()));
.
.
.
在线上
btnInSituActivitySend = (Button)findViewById(R.id.btnInSituActivitySend_id);
btnInSituActivitySend 被定义为Button btnInSituActivitySend;，btnInSituActivitySend_id 在 xml 文件中被定义为
<Button
android:id="@+id/btnInSituActivitySend_id"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="InSituActivitySend_click"
android:text="@string/btnInSituActivitySend_string" />
总结：
我没有将 TextView 类型转换为按钮。那我为什么会收到这个错误？
编辑（面向未来的 Google 同事）：
这似乎是一个非常常见的问题，但很难找到解决方案，可能是由于错误描述的模糊性，而且看到这个问题并不能说明在 Google 上使用什么搜索词。 解决方案是清理项目。
Android.widget,textView cannot be cast to android.widget,button
android.widget.Button cannot be cast to android.widget.EditText
java.lang.ClassCastException: android.widget.TextView. Why am I getting this?
Google search
【问题讨论】：
标签： android android-layout android-xml