致命的例外：主要在android

Question

我是Android編程領域的一個非常初學者。 我只是想開發一個示例應用程序。 這裏的項目：

public class CalcActivity extends Activity implements OnClickListener{ 

EditText input = (EditText) findViewById(R.id.input); 
Button one = (Button) findViewById(R.id.button1); 
TextView out = (TextView) findViewById(R.id.output); 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_calc); 
    //one.setOnClickListener(this); 
} 
public void onClick(View v){ 

    input.setText("HI"); 
} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.calc, menu); 
    return true; 
} 

} 

Answer 1

試試這個

public class CalcActivity extends Activity implements OnClickListener { 

EditText input ; 
Button one ; 
TextView out; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_calc); 
    input = (EditText) findViewById(R.id.input); 
    one = (Button) findViewById(R.id.button1); 
    one.setOnClickListener(this); 
    out = (TextView) findViewById(R.id.output); 
    // one.setOnClickListener(this); 
} 

public void onClick(View v) { 
    switch (v.getId()) { 
    case R.id.button1: 
     input.setText("HI"); 
     Log.d("button clicked", "buttom"); 
     break; 
    } 
} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.calc, menu); 
    return true; 
} 

}

Answer 2

你沒有初始化的OnCreate中內部視圖（），因此你越來越強制關閉 所以初始化裏面的onCreate您的看法像這樣

EditText input; 
Button one ; 
TextView out; 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_calc); 
    input= (EditText) findViewById(R.id.input); 
    one = (Button) findViewById(R.id.button1); 
    out = (TextView) findViewById(R.id.output); 

}