在按钮上单击，切换到新的布局xml文件，现在使用按钮，但是如何使用片段？

Question

I am creating a Bluetooth app that requires a log in and/or sign up. I use a button click to switch to new layout xml file, but I need to not use buttons and figure out how to use fragments! When I have a button on the second page that gets clicked it crashes the app. Help :(

MainActivity.java

package com.example.chirp;

import android.app.Activity;
import android.app.FragmentTransaction;
import android.bluetooth.BluetoothAdapter;
import android.content.res.Configuration;
import android.os.Bundle;
import android.support.v4.app.FragmentManager;
import android.view.KeyEvent;
import android.view.Menu;
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);
        setContentView(R.layout.activity_main);

        BluetoothAdapter bluetooth = BluetoothAdapter.getDefaultAdapter() ;
        bluetooth.setName("Chirp Bluetooth");

        String status; {
            if (bluetooth != null)
            {

                if (bluetooth.isEnabled())
                {
                    String mydeviceaddress = bluetooth.getAddress();
                    String mydevicename = bluetooth.getName();
//                  String state = bluetooth.getState();
//                  status = mydevicename + ":" + mydeviceaddress + ":" + state;
                }
                else
                {
                    status = "Bluetooth is not Enabled.";
                }
                }
//          Toast.makeText(this, status, Toast.LENGTH_LONG).show();
            }   

//        Configuration config = getResources().getConfiguration();
//
//        FragmentManager fragmentManager = getFragmentManager();
//        FragmentTransaction fragmentTransaction = 
//        fragmentManager.beginTransaction();
//       
        Button quickfindbutton = (Button) findViewById(R.id.qfbutton);
        quickfindbutton.setOnClickListener(new OnClickListener(){
            public void onClick(View v){

            }
        });

        Button loginbutton = (Button) findViewById(R.id.button1);
        loginbutton.setOnClickListener(new OnClickListener(){
            public void onClick(View v){
                setContentView(R.layout.loginscreen);               

        };

        });


    Button signupbutton = (Button) findViewById(R.id.button2);
    signupbutton.setOnClickListener(new OnClickListener(){
        public void onClick(View v){
            setContentView(R.layout.signupscreen);
        }
         });

//    Button login = (Button) findViewById(R.id.login);
//    login.setOnClickListener(new OnClickListener(){
//      public void onClick(View v){
//          setContentView(R.layout.devicepage);
//      }
//       });




    }

    public void showToast(String message) {

        Toast toast = Toast.makeText(getApplicationContext(), message,
                Toast.LENGTH_SHORT);

        toast.show();

    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event)  {
        if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
           setContentView(R.layout.activity_main);
           return true;

        }
        return super.onKeyDown(keyCode, event);
    }

    @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; 
    }

//    public void newMessage(View v){
//      Intent intent = new Intent(this,loginscreen.class);
//      startActivity(intent);
//    }
    }

Answer 1

setContentView() should be in onCreate() method within first few lines. Otherwise it will not work. If you need to change the layout after click on the button what you can do is, use SharedPreferences .

Check the saved item in shared Preferences before and then use setContentView() method in onCreate() . Inside the button onClick () method save the wanted layout in SharedPreferences . Then write the code to restart the application.

Answer 2

Check out this link:

http://developer.android.com/guide/components/fragments.html

And also check if your second activity is registered in the manifest.xml.