_动力学知识库

问题描述:

I know that the function onCreate() used to construct the activity and UI components but when I try put setContentView(R.layout.activity_main) in the function onStart() or onResume(), the UI components apper , that's why?

package com.example.E001;
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.Toast;
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
protected void onStart() {
super.onStart();
setContentView(R.layout.activity_main);
//setContentView(R.layout.demo);
Button btn_welcome = (Button)this.findViewById(R.id.welcome_msg);
btn_welcome.setText(R.string.hello_world);
}
}

网友答案:

You should put it in the onCreate, like this:

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

For more info look in the Android Documentation

What I think you are trying to do with the layout.demo is inflate a extra view in your MainActivity. Then you should NOT use setContentView(). For inflating a view in a layout you can use the LayoutInflater.

Note: If this does not completely answer your question, than I don't understand your question correctly.