Java A_类不能转换为B_类？
如果我的文件名让你不感兴趣，我向你道歉 因此，我得到的实际错误是：Java A_类不能转换为B_类？,java,android,android-studio,Java,Android,Android Studio,如果我的文件名让你不感兴趣，我向你道歉 因此，我得到的实际错误是： pwnavor.ljv1.Home_Page cannot be cast to pwnavor.ljv1.MainActivity 我不知道这意味着什么，环顾四周后，我意识到它涵盖了一些不同的东西。当我遇到此错误时，我的应用程序正在尝试运行一个活动，该活动通过选项卡式菜单中的recyclerview处理rss提要。如果我自己运行MainActivity，它可以正常工作，但是，当我尝试在主页中运行它时，我会出现此错误，显然，如
pwnavor.ljv1.Home_Page cannot be cast to pwnavor.ljv1.MainActivity
package pwnavor.ljv1;
import android.os.Bundle;
import android.support.design.widget.TabLayout;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
public class Home_Page extends AppCompatActivity {
/**
* The {@link android.support.v4.view.PagerAdapter} that will provide
* fragments for each of the sections. We use a
* {@link FragmentPagerAdapter} derivative, which will keep every
* loaded fragment in memory. If this becomes too memory intensive, it
* may be best to switch to a
* {@link android.support.v4.app.FragmentStatePagerAdapter}.
*/
private SectionsPagerAdapter mSectionsPagerAdapter;
/**
* The {@link ViewPager} that will host the section contents.
*/
private ViewPager mViewPager;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home__page);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
// Create the adapter that will return a fragment for each of the three
// primary sections of the activity.
mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
// Set up the ViewPager with the sections adapter.
mViewPager = (ViewPager) findViewById(R.id.container);
mViewPager.setAdapter(mSectionsPagerAdapter);
TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
tabLayout.setupWithViewPager(mViewPager);
}
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_home__page, menu);
return true;
}
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
/**
* The fragment argument representing the section number for this
* fragment.
*/
private static final String ARG_SECTION_NUMBER = "section_number";
/**
* Returns a new instance of this fragment for the given section
* number.
*/
public static PlaceholderFragment newInstance(int sectionNumber) {
PlaceholderFragment fragment = new PlaceholderFragment();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
if(getArguments().getInt(ARG_SECTION_NUMBER)==1)
{
/**=================================================================
* where my issue starts
*/
MainActivity parent=(MainActivity) getActivity();
return new View(parent);
/**
* ==================================================================
*/
}
else if(getArguments().getInt(ARG_SECTION_NUMBER)==2)
{
View rootView = inflater.inflate(R.layout.fragment_home__page, container, false);
TextView textView = (TextView) rootView.findViewById(R.id.Home);
textView.setText(getString(R.string.section_format, getArguments().getInt(ARG_SECTION_NUMBER)));
return rootView;
}
else
{
View rootView = inflater.inflate(R.layout.fragment_home__page, container, false);
TextView textView = (TextView) rootView.findViewById(R.id.Home);
textView.setText(getString(R.string.section_format, getArguments().getInt(ARG_SECTION_NUMBER)));
return rootView;
}
}
}
/**
* A {@link FragmentPagerAdapter} that returns a fragment corresponding to
* one of the sections/tabs/pages.
*/
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
public Fragment getItem(int position) {
// getItem is called to instantiate the fragment for the given page.
// Return a PlaceholderFragment (defined as a static inner class below).
return PlaceholderFragment.newInstance(position + 1);
}
public int getCount() {
// Show 3 total pages.
return 3;
}
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return "Home";
case 1:
return "SECTION 2";
case 2:
return "SECTION 3";
}
return null;
}
}
package pwnavor.ljv1;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.RecyclerView;
public class MainActivity extends AppCompatActivity {
RecyclerView recyclerView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView= (RecyclerView) findViewById(R.id.recyclerView);
ReadRss readRss = new ReadRss(this, recyclerView);
readRss.execute();
}
}
01/15 14:10:15: Launching app
Cold swapped changes.
$ adb shell am start -n "pwnavor.ljv1/pwnavor.ljv1.Launch_Screen" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER
Connected to process 6328 on device Nexus_5X_API_23 [emulator-5554]
W/System: ClassLoader referenced unknown path: /data/app/pwnavor.ljv1-2/lib/x86
I/InstantRun: Instant Run Runtime started. Android package is pwnavor.ljv1, real application class is null.
W/System: ClassLoader referenced unknown path: /data/app/pwnavor.ljv1-2/lib/x86
I/FirebaseInitProvider: FirebaseApp initialization unsuccessful
W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
D/OpenGLRenderer: Use EGL_SWAP_BEHAVIOR_PRESERVED: true
[ 01-15 14:10:18.618 6328: 6328 D/ ]
HostConnection::get() New Host Connection established 0xaa202180, tid 6328
[ 01-15 14:10:18.619 6328: 6328 W/ ]
Process pipe failed
[ 01-15 14:10:18.643 6328: 6346 D/ ]
HostConnection::get() New Host Connection established 0xaa202540, tid 6346
I/OpenGLRenderer: Initialized EGL, version 1.4
E/EGL_emulation: tid 6346: eglSurfaceAttrib(1165): error 0x3009 (EGL_BAD_MATCH)
W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface 0xaa414b00, error=EGL_BAD_MATCH
I/Choreographer: Skipped 31 frames! The application may be doing too much work on its main thread.
I/TextInputLayout: EditText added is not a TextInputEditText. Please switch to using that class instead.
I/TextInputLayout: EditText added is not a TextInputEditText. Please switch to using that class instead.
E/EGL_emulation: tid 6346: eglSurfaceAttrib(1165): error 0x3009 (EGL_BAD_MATCH)
W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface 0xaa231f80, error=EGL_BAD_MATCH
E/Surface: getSlotFromBufferLocked: unknown buffer: 0xae473a00
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: pwnavor.ljv1, PID: 6328
java.lang.ClassCastException: pwnavor.ljv1.Home_Page cannot be cast to pwnavor.ljv1.MainActivity
at pwnavor.ljv1.Home_Page$PlaceholderFragment.onCreateView(Home_Page.java:128)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:2080)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1108)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1290)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:801)
at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:1638)
at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:679)
at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:143)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1240)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1088)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1614)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:700)
at android.support.design.widget.HeaderScrollingViewBehavior.onMeasureChild(HeaderScrollingViewBehavior.java:90)
at android.support.design.widget.AppBarLayout$ScrollingViewBehavior.onMeasureChild(AppBarLayout.java:1364)
at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:765)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
at android.view.View.measure(View.java:18788)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2100)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1216)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1452)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
at android.view.Choreographer.doCallbacks(Choreographer.java:670)
at android.view.Choreographer.doFrame(Choreographer.java:606)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:61
I/Process: Sending signal. PID: 6328 SIG: 9
Application terminated.
使用完整stacktrace编辑您的类层次结构是：
01/15 14:10:15: Launching app
Cold swapped changes.
$ adb shell am start -n "pwnavor.ljv1/pwnavor.ljv1.Launch_Screen" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER
Connected to process 6328 on device Nexus_5X_API_23 [emulator-5554]
W/System: ClassLoader referenced unknown path: /data/app/pwnavor.ljv1-2/lib/x86
I/InstantRun: Instant Run Runtime started. Android package is pwnavor.ljv1, real application class is null.
W/System: ClassLoader referenced unknown path: /data/app/pwnavor.ljv1-2/lib/x86
I/FirebaseInitProvider: FirebaseApp initialization unsuccessful
W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
D/OpenGLRenderer: Use EGL_SWAP_BEHAVIOR_PRESERVED: true
[ 01-15 14:10:18.618 6328: 6328 D/ ]
HostConnection::get() New Host Connection established 0xaa202180, tid 6328
[ 01-15 14:10:18.619 6328: 6328 W/ ]
Process pipe failed
[ 01-15 14:10:18.643 6328: 6346 D/ ]
HostConnection::get() New Host Connection established 0xaa202540, tid 6346
I/OpenGLRenderer: Initialized EGL, version 1.4
E/EGL_emulation: tid 6346: eglSurfaceAttrib(1165): error 0x3009 (EGL_BAD_MATCH)
W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface 0xaa414b00, error=EGL_BAD_MATCH
I/Choreographer: Skipped 31 frames! The application may be doing too much work on its main thread.
I/TextInputLayout: EditText added is not a TextInputEditText. Please switch to using that class instead.
I/TextInputLayout: EditText added is not a TextInputEditText. Please switch to using that class instead.
E/EGL_emulation: tid 6346: eglSurfaceAttrib(1165): error 0x3009 (EGL_BAD_MATCH)
W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface 0xaa231f80, error=EGL_BAD_MATCH
E/Surface: getSlotFromBufferLocked: unknown buffer: 0xae473a00
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: pwnavor.ljv1, PID: 6328
java.lang.ClassCastException: pwnavor.ljv1.Home_Page cannot be cast to pwnavor.ljv1.MainActivity
at pwnavor.ljv1.Home_Page$PlaceholderFragment.onCreateView(Home_Page.java:128)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:2080)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1108)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1290)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:801)
at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:1638)
at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:679)
at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:143)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1240)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1088)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1614)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:700)
at android.support.design.widget.HeaderScrollingViewBehavior.onMeasureChild(HeaderScrollingViewBehavior.java:90)
at android.support.design.widget.AppBarLayout$ScrollingViewBehavior.onMeasureChild(AppBarLayout.java:1364)
at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:765)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
at android.view.View.measure(View.java:18788)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2100)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1216)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1452)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
at android.view.Choreographer.doCallbacks(Choreographer.java:670)
at android.view.Choreographer.doFrame(Choreographer.java:606)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:61
I/Process: Sending signal. PID: 6328 SIG: 9
Application terminated.
class Home_Page extends AppCompatActivity
class MainActivity extends AppCompatActivity
class Dog extends Animal
class Cat extends Animal
同样，您不能将主页强制转换为MainActivity。请提供完整的stacktraceIt，这意味着它所说的ClassA不是ClassB的实例，因此您不能以这种方式强制转换，因为这毫无意义。错误发生的地方是演员的位置，这就是问题所在。谢谢你，我不明白为什么我会因为问问题而被否决。让我甚至不敢麻烦寻求帮助，甚至不敢学习编码。有没有办法在主页上运行MainActivity？或者我必须把它写下来，让猫变成一个片段，叫做狗玩具，狗跑狗玩具？