在多页的android应用中，MainActivity类型的封闭实例是不可访问的

Question

我试图使多个按钮打开不同的XML页面。我已经得到了这个beforemain.java，出于某种原因，我得到了错误"没有类型的MainActivity的封闭实例是可访问的范围"。下面是我的代码:

package com.dogger20011.app;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public abstract class beforemain extends MainActivity implements OnClickListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_main);
Button mBtn1 = (Button) findViewById(R.id.button1);
Button mBtn2 = (Button) findViewById(R.id.button2); //Just like #1
mBtn1.setOnClickListener(this);
mBtn2.setOnClickListener(this); //Also like #1
}
@Override
public void onClick(View v) {
switch(v.getId()) { //Get the id of the button that was clicked
case R.id.button1:
    Intent i = new Intent(MainActivity.this, Activity2.class);
    startActivity(i);
    break;
case R.id.button2:
    Intent i1 = new Intent(MainActivity.this, Activity3.class);
    startActivity(i1);
    break;
}
}}

这里是Button 1和Button 2的错误所在

case R.id.button2:
    Intent i1 = new Intent(MainActivity.this, Activity3.class);

我做错了什么?

编辑这是我的Manifest

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.dogger20011.app"
android:versionCode="1"
android:versionName="1.0.5Beta1"
android:installLocation="auto" >
<uses-sdk
    android:minSdkVersion="8"
    android:targetSdkVersion="19" />
<uses-permission
    android:name="android.permission.INTERNET"
    android:maxSdkVersion="19">
</uses-permission>

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name">

    <activity
        android:label="@string/app_name"
        android:name="beforemain">

            <intent-filter>
             <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
            </activity>

    <activity
        android:label="@string/app_name"
        android:name=".Activity2"></activity>
    <activity
        android:label="@string/app_name"
        android:name=".Activity3"></activity>    


</application>
</manifest>

编辑2 下面是我的错误日志:

06-16 01:36:55.379: E/AndroidRuntime(1066): FATAL EXCEPTION: main
06-16 01:36:55.379: E/AndroidRuntime(1066): Process: com.dogger20011.app, PID: 1066
06-16 01:36:55.379: E/AndroidRuntime(1066): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.dogger20011.app/com.dogger20011.app.beforemain}: java.lang.IllegalArgumentException: No view found for id 0x7f05003c (com.dogger20011.app:id/container) for fragment PlaceholderFragment{b3d37f00 #0 id=0x7f05003c}
06-16 01:36:55.379: E/AndroidRuntime(1066):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
06-16 01:36:55.379: E/AndroidRuntime(1066):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
06-16 01:36:55.379: E/AndroidRuntime(1066):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
06-16 01:36:55.379: E/AndroidRuntime(1066):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
06-16 01:36:55.379: E/AndroidRuntime(1066):     at android.os.Handler.dispatchMessage(Handler.java:102)
06-16 01:36:55.379: E/AndroidRuntime(1066):     at android.os.Looper.loop(Looper.java:136)
06-16 01:36:55.379: E/AndroidRuntime(1066):     at android.app.ActivityThread.main(ActivityThread.java:5017)
06-16 01:36:55.379: E/AndroidRuntime(1066):     at java.lang.reflect.Method.invokeNative(Native Method)
06-16 01:36:55.379: E/AndroidRuntime(1066):     at java.lang.reflect.Method.invoke(Method.java:515)
06-16 01:36:55.379: E/AndroidRuntime(1066):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
06-16 01:36:55.379: E/AndroidRuntime(1066):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
06-16 01:36:55.379: E/AndroidRuntime(1066):     at dalvik.system.NativeStart.main(Native Method)
06-16 01:36:55.379: E/AndroidRuntime(1066): Caused by: java.lang.IllegalArgumentException: No view found for id 0x7f05003c (com.dogger20011.app:id/container) for fragment PlaceholderFragment{b3d37f00 #0 id=0x7f05003c}
06-16 01:36:55.379: E/AndroidRuntime(1066):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:930)
06-16 01:36:55.379: E/AndroidRuntime(1066):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1115)
06-16 01:36:55.379: E/AndroidRuntime(1066):     at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
06-16 01:36:55.379: E/AndroidRuntime(1066):     at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1478)
06-16 01:36:55.379: E/AndroidRuntime(1066):     at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:570)
06-16 01:36:55.379: E/AndroidRuntime(1066):     at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1171)
06-16 01:36:55.379: E/AndroidRuntime(1066):     at android.app.Activity.performStart(Activity.java:5241)
06-16 01:36:55.379: E/AndroidRuntime(1066):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2168)
06-16 01:36:55.379: E/AndroidRuntime(1066):     ... 11 more

编辑3 下面是我的MainActivity，它包含占位符片段:

package com.dogger20011.app;
import android.support.v7.app.ActionBarActivity;
import android.support.v4.app.Fragment;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.os.Build;
public class MainActivity extends ActionBarActivity {
private Context context;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    if (savedInstanceState == null) {
        getSupportFragmentManager().beginTransaction()
                .add(R.id.container, new  
PlaceholderFragment()).commit();
    }
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}
@Override
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();
    if (id == R.id.Downloads) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}
/**
 * A placeholder fragment containing a simple view.
 */
public static class PlaceholderFragment extends Fragment {
    private static final Context context = null;
    public PlaceholderFragment() {
    }
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.fragment_main, container,
                false);
        return rootView; 


}
}
}

Answer 1

我无法在您的activity_main xml中找到id R.id.container，它要么您将id放在布局中，要么在您的add方法中删除R.id.container

改变这个

if (savedInstanceState == null) {
    getSupportFragmentManager().beginTransaction()
            .add(R.id.container, new  

PlaceholderFragment ()) .commit ();}

if (savedInstanceState == null) {
    getSupportFragmentManager().beginTransaction()
            .add(new  
PlaceholderFragment(), "placeholder").commit();
    }

Answer 2

修改

new Intent(MainActivity.this, Activity3.class);

到

new Intent(beforemain.this, Activity3.class);

这是必要的，因为您要创建的充当侦听器的匿名类位于beforemain类的内部，而不是MainActivity类。