我想将一个新类附加到我在XML中定义的ImageView。以下代码有效，但仅适用于视图类型。当我将类型更改为ImageView，如下所示，我得到了ClassCastException。
这是我的article_view.xml文件：
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/bg_color"
>
<LinearLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:weightSum="600">
<ImageView
android:id="@+id/mybutton1"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="75"
class="com.example.customui2.MainActivity$ArticleFragment$MyButton"
android:contentDescription="@string/logo_desc"
android:src="@drawable/menu_button"
android:text="@string/button1"
android:textColor="@color/button1_color"
android:textSize="45sp" />
</LinearLayout>
</RelativeLayout>
和这样的源文件：
public class MainActivity extends FragmentActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (findViewById(R.id.fragment_container) != null) {
// However, if we're being restored from a previous state,
// then we don't need to do anything and should return or else
// we could end up with overlapping fragments.
if (savedInstanceState != null) {
return;
}
// Create a new Fragment to be placed in the activity layout
ArticleFragment firstFragment = new ArticleFragment();
// In case this activity was started with special instructions from an
// Intent, pass the Intent's extras to the fragment as arguments
firstFragment.setArguments(getIntent().getExtras());
// Add the fragment to the 'fragment_container' FrameLayout
getSupportFragmentManager().beginTransaction()
.add(R.id.fragment_container, firstFragment).commit();
}
}
public static class ArticleFragment extends Fragment {
// Animation
Animation animFadein;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View rootView = inflater.inflate(R.layout.article_view, container, false);
MyButton button1 = (MyButton) rootView.findViewById(R.id.mybutton1);
// load the animation
animFadein = AnimationUtils.loadAnimation(rootView.getContext().getApplicationContext(),
R.anim.fade_in);
button1.startAnimation(animFadein);
return rootView;
}
public static class MyButton extends View implements
{
Bitmap backgroundImage;
Paint backgroundPaint;
public MyButton(Context context, AttributeSet attrs) {
super(context, attrs);
backgroundImage = BitmapFactory.decodeResource(context.getResources(), R.drawable.ic_launcher);
backgroundPaint = new Paint();
}
@Override
protected void onDraw(Canvas canvas)
{
canvas.drawBitmap(backgroundImage, 0, 0, backgroundPaint);
super.onDraw(canvas);
}
};
}
}
现在我在这一行收到错误ClassCastException：
MyButton button1 = (MyButton) rootView.findViewById(R.id.mybutton1);
这里是logcat：
07-16 17:35:36.855: E/AndroidRuntime(7039): FATAL EXCEPTION: main
07-16 17:35:36.855: E/AndroidRuntime(7039): Process: com.example.customui2, PID: 7039
07-16 17:35:36.855: E/AndroidRuntime(7039): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.customui2/com.example.customui2.MainActivity}: java.lang.ClassCastException: android.widget.ImageView cannot be cast to com.example.customui2.MainActivity$ArticleFragment$MyButton
07-16 17:35:36.855: E/AndroidRuntime(7039): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
07-16 17:35:36.855: E/AndroidRuntime(7039): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
07-16 17:35:36.855: E/AndroidRuntime(7039): at android.app.ActivityThread.access$800(ActivityThread.java:135)
07-16 17:35:36.855: E/AndroidRuntime(7039): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
07-16 17:35:36.855: E/AndroidRuntime(7039): at android.os.Handler.dispatchMessage(Handler.java:102)
07-16 17:35:36.855: E/AndroidRuntime(7039): at android.os.Looper.loop(Looper.java:136)
07-16 17:35:36.855: E/AndroidRuntime(7039): at android.app.ActivityThread.main(ActivityThread.java:5017)
07-16 17:35:36.855: E/AndroidRuntime(7039): at java.lang.reflect.Method.invokeNative(Native Method)
07-16 17:35:36.855: E/AndroidRuntime(7039): at java.lang.reflect.Method.invoke(Method.java:515)
07-16 17:35:36.855: E/AndroidRuntime(7039): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
07-16 17:35:36.855: E/AndroidRuntime(7039): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
07-16 17:35:36.855: E/AndroidRuntime(7039): at dalvik.system.NativeStart.main(Native Method)
07-16 17:35:36.855: E/AndroidRuntime(7039): Caused by: java.lang.ClassCastException: android.widget.ImageView cannot be cast to com.example.customui2.MainActivity$ArticleFragment$MyButton
07-16 17:35:36.855: E/AndroidRuntime(7039): at com.example.customui2.MainActivity$ArticleFragment.onCreateView(MainActivity.java:110)
07-16 17:35:36.855: E/AndroidRuntime(7039): at android.support.v4.app.Fragment.performCreateView(Fragment.java:1504)
07-16 17:35:36.855: E/AndroidRuntime(7039): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:942)
07-16 17:35:36.855: E/AndroidRuntime(7039): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1121)
07-16 17:35:36.855: E/AndroidRuntime(7039): at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
07-16 17:35:36.855: E/AndroidRuntime(7039): at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1484)
07-16 17:35:36.855: E/AndroidRuntime(7039): at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:571)
07-16 17:35:36.855: E/AndroidRuntime(7039): at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1171)
07-16 17:35:36.855: E/AndroidRuntime(7039): at android.app.Activity.performStart(Activity.java:5241)
07-16 17:35:36.855: E/AndroidRuntime(7039): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2168)
07-16 17:35:36.855: E/AndroidRuntime(7039): ... 11 more
07-16 17:35:39.895: I/Process(7039): Sending signal. PID: 7039 SIG: 9
我应该更改什么才能将类附加到视图以外的类型，如ImageView？
答案 0 :(得分：2)
如果要将ImageView强制转换为ImageView，MyButton必须扩展ImageView。
如果您的MyButton类只是一个View，它缺少您尝试使用的所有ImageView组件。也许你只能使用常规的ImageView。
编辑：
您可以使用小写视图标记+ class属性在XML中引用MyButton类：
<view
android:id="@+id/mybutton1"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="75"
class="com.example.customui2.MainActivity$ArticleFragment$MyButton"
android:contentDescription="@string/logo_desc"
android:src="@drawable/menu_button"
android:text="@string/button1"
android:textColor="@color/button1_color"
android:textSize="45sp" />
然后声明你的静态类：
public static class MyButton extends ImageView
我测试了它并且它没有崩溃。