我在開發Android應用時遇到錯誤

Question

我一直收到的錯誤是「應用程序Test（process com.example.test）已意外停止，請再試一次」。在模擬器上啓動應用程序時發生此錯誤。下面是代碼：

MainActivity 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
// setContentView(R.layout.activity_main); 
    TextView myText = new TextView (this); 
    myText.setText("Hello World!"); 
    setContentView(myText); 
    myDemoButton(); 

} 
private void myDemoButton() { 
    Button displayButton = (Button) findViewById(R.id.btnTesting); 
    displayButton.setOnClickListener(new View.OnClickListener() { 

     @Override 
     public void onClick(View v) { 
      Log.i("MyApp","Welcome To Android!"); 
      Toast.makeText(MainActivity.this,"Welcome To Android!",Toast.LENGTH_LONG).show(); 

     } 
    }); 

} 

@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; 
}} 

清單XML代碼

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

<uses-sdk 
    android:minSdkVersion="8" 
    android:targetSdkVersion="18" /> 

<application 
    android:allowBackup="true" 
    android:icon="@drawable/ic_launcher" 
    android:label="@string/app_name" 
    android:theme="@style/AppTheme" > 
    <activity 
     android:name="com.example.test.MainActivity" 
     android:label="@string/app_name" > 
     <intent-filter> 
      <action android:name="android.intent.action.MAIN" /> 

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

活動主要XML

<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:paddingBottom="@dimen/activity_vertical_margin" 
android:paddingLeft="@dimen/activity_horizontal_margin" 
android:paddingRight="@dimen/activity_horizontal_margin" 
android:paddingTop="@dimen/activity_vertical_margin" 
tools:context=".MainActivity" > 

<TextView 
    android:id="@+id/textView1" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:text="@string/hello_world" /> 

<Button 
    android:id="@+id/btnTesting" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignLeft="@+id/textView1" 
    android:layout_below="@+id/textView1" 
    android:layout_marginTop="22dp" 
    android:text="Tap" /> 

    </RelativeLayout> 

Answer 1

變化主要與此

@Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     myDemoButton(); 

    } 
    private void myDemoButton() { 
     Button displayButton = (Button) findViewById(R.id.btnTesting); 
     displayButton.setOnClickListener(new View.OnClickListener() { 

      @Override 
      public void onClick(View v) { 
       Log.i("MyApp","Welcome To Android!"); 
       Toast.makeText(MainActivity.this,"Welcome To Android!",Toast.LENGTH_LONG).show(); 

      } 
     }); 

    } 

@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; 
}} 

活動