安卓模拟器运行出现unfortunately，xxx has stoped是什么原因啊，小白刚学

Question

activity_main.xml代码：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"

<TextView
    android:id="@+id/text_view"
    android:layout_width="match_parent"  
    android:layout_height="wrap_content"
    android:text="This is TextView" />
<Button
    android:id="@+id/button"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Button"/>
<EditText
    android:id="@+id/edit_text"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_below="@+id/button"
    android:layout_marginTop="14dp"
    android:ems="10"
    android:hint="Type something here" >
    <requestFocus />
</EditText>

MainActivity.java代码：

package com.example.class3;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity {

private Button button;

private EditText editText;

@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.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

@Override

protected void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Button button = (Button) findViewById(R.id.button);
    editText=(EditText) findViewById(R.id.edit_text);
    button.setOnClickListener((OnClickListener) this);
}

public void onClick(View v){
    switch(v.getId()){
    case R.id.button:
        String inputText=editText.getText().toString();
        Toast.makeText(MainActivity.this,inputText,
                Toast.LENGTH_SHORT).show();
        break;
        default:
            break;
    }
}

}

Answer 1

感觉自己排版都好乱- -