空值一例

想用addView添加Button等widget..

		linelayout = (LinearLayout)findViewById(R.id.linelayout);
		Intent it = getIntent();
		String username = it.getStringExtra("username"); 
		et_mobile = new TextView(this);
		btn = new Button(this);
		LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(
		LinearLayout.LayoutParams.WRAP_CONTENT,
		LinearLayout.LayoutParams.WRAP_CONTENT);
		params.topMargin = 0;
		params.gravity = Gravity.TOP | Gravity.CENTER_HORIZONTAL;
		Log.d(TAG,params.toString()+"|"+linelayout);
		et_mobile.setText(username);
linelayout.addView(et_mobile, params);

发现总是报空指针Exception....

检查发现是没有:

setContentView(R.layout.intent003);

的原因