关于android：不幸的是myapp已经停止了

Unfortunately myapp has stopped

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我的申请已经停止了。项目将场景改为主应用到作业列表，但是，作业列表改为练习列表，？我正在Emulator上获取这些"不幸的是，应用程序已停止"。这是我的类。我也有致命的，除了？n在LogCAT上。

应用程序主.java

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import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class ApplicationMain extends Activity {
/** Called when the activity is first created. */
EditText nameEditCtrl;
Button btnCtlr;
String name;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
nameEditCtrl = (EditText) findViewById(R.id.editText1);
btnCtlr = (Button) findViewById(R.id.button1);
btnCtlr.setOnClickListener(new ButtonClickHandler());
}

public class ButtonClickHandler implements View.OnClickListener {
public void onClick(View view) {
if (nameEditCtrl != null && nameEditCtrl.getText().length() != 0) {
name = nameEditCtrl.getText().toString();
} else {
name ="Guest";
}
Intent intObj = new Intent(ApplicationMain.this,
JobList.class);
intObj.putExtra("USERNAME", name);
startActivity(intObj);
}
}
}

乔布斯

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import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.TextView;

public class JobList extends Activity {
TextView greetMsg;
ImageButton ib;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.joblist);
greetMsg = (TextView) findViewById(R.id.textView1);
Intent intename = getIntent();
String uname = (String) intename.getSerializableExtra("USERNAME");
greetMsg.setText("Welcome" + uname);

ib = (ImageButton) findViewById(R.id.imageButton1);
ib.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent intObj = new Intent(JobList.this,ExerciseList.class);
startActivity(intObj);
}
});

}

}

Java语言

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import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.TextView;

public class ExerciseList extends Activity {

ImageButton iz;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.exerciselist);

iz = (ImageButton) findViewById(R.id.imageButton2);
iz.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {

Intent intObj = new Intent(ExerciseList.this,
ApplicationMain.class);
//intObj.putExtra("USERNAME", name);
startActivity(intObj);
}
});

}
}

安卓宣言

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<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.prgguru.android"
android:versionCode="1"
android:versionName="1.0">

<uses-sdk android:minSdkVersion="14" android:targetSdkVersion="15" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

<application
android:icon="@drawable/ic_launcher"
android:label="@string/app_name">
<activity
android:name=".ApplicationMain"
android:label="@string/app_name">
<intent-filter>

<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".JobList"
android:label="@string/app_name">
</activity>
</application>

</manifest>