在片段中需要帮助(Android)
Need Help in Fragments(Android)
我刚开始学习android。所以我在做主题片段时,当我决定自己创建一个片段时,以下是我编写的代码。但是在 运行 上,模拟器显示的代码 "fragment2 has stopped "。
请查看我的代码并告诉我哪里出错了。提前致谢。
1.fragment
package com.example.adi.fragment2;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import org.w3c.dom.Text;
public class MainActivity extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.activity_main,container,false);
final EditText editText = (EditText)view.findViewById(R.id.editText);
final TextView textView = (TextView)view.findViewById(R.id.textView);
Button button = (Button) view.findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
textView.setText(editText.getText().toString());
}
});
return view;
}
}
2.main 启动器 activity
package com.example.adi.fragment2;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
public class Launcher extends FragmentActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
FragmentManager fm = getSupportFragmentManager();
Fragment fragment = fm.findFragmentById(R.id.box);
if(fragment==null) {
fragment = new MainActivity();
fm.beginTransaction().add(R.id.box, fragment).commit();
}
}
}
编辑:这是日志状态
01-07 06:05:26.423 2183-2183/? I/art: Late-enabling -Xcheck:jni
01-07 06:05:26.423 2183-2183/? W/art: Unexpected CPU variant for X86 using defaults: x86
01-07 06:05:26.550 2183-2183/com.example.adi.fragment2 W/System: ClassLoader referenced unknown path: /data/app/com.example.adi.fragment2-2/lib/x86
01-07 06:05:26.573 2183-2183/com.example.adi.fragment2 I/InstantRun: Instant Run Runtime started. Android package is com.example.adi.fragment2, real application class is null.
01-07 06:05:26.944 2183-2183/com.example.adi.fragment2 W/System: ClassLoader referenced unknown path: /data/app/com.example.adi.fragment2-2/lib/x86
01-07 06:05:26.985 2183-2183/com.example.adi.fragment2 D/AndroidRuntime: Shutting down VM
01-07 06:05:26.986 2183-2183/com.example.adi.fragment2 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.adi.fragment2, PID: 2183
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.adi.fragment2/com.example.adi.fragment2.MainActivity}: java.lang.ClassCastException: com.example.adi.fragment2.MainActivity cannot be cast to android.app.Activity
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2548)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
Caused by: java.lang.ClassCastException: com.example.adi.fragment2.MainActivity cannot be cast to android.app.Activity
at android.app.Instrumentation.newActivity(Instrumentation.java:1078)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2538)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
我没有完整的代码,所以我不能 100% 确定。但是如果已经有下面显示的默认片段,而不是尝试在片段管理器上使用替换可能会修复它。
改变
fm.beginTransaction().add(R.id.box, fragment).commit();
到
fm.beginTransaction().replace(R.id.box, fragment).commit();
您没有将 FragmentTransaction 添加到代码中。
别忘了导入
在您的 onCreate 方法中执行此操作
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
ft.replace(R.id.content_frame, fragment);//add this only if add() doesn't work
ft.commit();
别忘了导入
import android.support.v4.app.FragmentTransaction;
并确保您只为所有方法导入了这个class
这 class 允许您向后兼容以前的版本。
这应该可以解决。
快乐编码。
仔细看看
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.adi.fragment2/com.example.adi.fragment2.MainActivity}: java.lang.ClassCastException: com.example.adi.fragment2.MainActivity cannot be cast to android.app.Activity
它说 com.example.adi.fragment2.MainActivity cannot be cast to android.app.Activity
。你的 MainActivity
实际上是一个 Fragment
public class MainActivity extends Fragment{
}
为您的 类 使用有意义的名称。
这是神奇的日志行:
java.lang.ClassCastException: com.example.adi.fragment2.MainActivity cannot be cast to android.app.Activity
基本上您的主要 activity 正在扩展 FragmentActivity class,并且我假设在您的片段 Xml 文件中您正在使用 android.app.Fragment
您也可以参考此 answer 了解更多信息
我刚开始学习android。所以我在做主题片段时,当我决定自己创建一个片段时,以下是我编写的代码。但是在 运行 上,模拟器显示的代码 "fragment2 has stopped "。 请查看我的代码并告诉我哪里出错了。提前致谢。
1.fragment
package com.example.adi.fragment2;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import org.w3c.dom.Text;
public class MainActivity extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.activity_main,container,false);
final EditText editText = (EditText)view.findViewById(R.id.editText);
final TextView textView = (TextView)view.findViewById(R.id.textView);
Button button = (Button) view.findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
textView.setText(editText.getText().toString());
}
});
return view;
}
}
2.main 启动器 activity
package com.example.adi.fragment2;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
public class Launcher extends FragmentActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
FragmentManager fm = getSupportFragmentManager();
Fragment fragment = fm.findFragmentById(R.id.box);
if(fragment==null) {
fragment = new MainActivity();
fm.beginTransaction().add(R.id.box, fragment).commit();
}
}
}
编辑:这是日志状态
01-07 06:05:26.423 2183-2183/? I/art: Late-enabling -Xcheck:jni
01-07 06:05:26.423 2183-2183/? W/art: Unexpected CPU variant for X86 using defaults: x86
01-07 06:05:26.550 2183-2183/com.example.adi.fragment2 W/System: ClassLoader referenced unknown path: /data/app/com.example.adi.fragment2-2/lib/x86
01-07 06:05:26.573 2183-2183/com.example.adi.fragment2 I/InstantRun: Instant Run Runtime started. Android package is com.example.adi.fragment2, real application class is null.
01-07 06:05:26.944 2183-2183/com.example.adi.fragment2 W/System: ClassLoader referenced unknown path: /data/app/com.example.adi.fragment2-2/lib/x86
01-07 06:05:26.985 2183-2183/com.example.adi.fragment2 D/AndroidRuntime: Shutting down VM
01-07 06:05:26.986 2183-2183/com.example.adi.fragment2 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.adi.fragment2, PID: 2183
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.adi.fragment2/com.example.adi.fragment2.MainActivity}: java.lang.ClassCastException: com.example.adi.fragment2.MainActivity cannot be cast to android.app.Activity
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2548)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
Caused by: java.lang.ClassCastException: com.example.adi.fragment2.MainActivity cannot be cast to android.app.Activity
at android.app.Instrumentation.newActivity(Instrumentation.java:1078)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2538)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
我没有完整的代码,所以我不能 100% 确定。但是如果已经有下面显示的默认片段,而不是尝试在片段管理器上使用替换可能会修复它。
改变
fm.beginTransaction().add(R.id.box, fragment).commit();
到
fm.beginTransaction().replace(R.id.box, fragment).commit();
您没有将 FragmentTransaction 添加到代码中。
别忘了导入
在您的 onCreate 方法中执行此操作
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
ft.replace(R.id.content_frame, fragment);//add this only if add() doesn't work
ft.commit();
别忘了导入
import android.support.v4.app.FragmentTransaction;
并确保您只为所有方法导入了这个class
这 class 允许您向后兼容以前的版本。
这应该可以解决。 快乐编码。
仔细看看
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.adi.fragment2/com.example.adi.fragment2.MainActivity}: java.lang.ClassCastException: com.example.adi.fragment2.MainActivity cannot be cast to android.app.Activity
它说 com.example.adi.fragment2.MainActivity cannot be cast to android.app.Activity
。你的 MainActivity
实际上是一个 Fragment
public class MainActivity extends Fragment{
}
为您的 类 使用有意义的名称。
这是神奇的日志行:
java.lang.ClassCastException: com.example.adi.fragment2.MainActivity cannot be cast to android.app.Activity
基本上您的主要 activity 正在扩展 FragmentActivity class,并且我假设在您的片段 Xml 文件中您正在使用 android.app.Fragment
您也可以参考此 answer 了解更多信息