Question

我正在开发一个简单的移动应用程序，用户登录并注销。当用户登录时，他可以访问多个页面（活动）。以下是我的mainactivity.java：

package org.hos.view;

import java.io.Serializable;

import org.hos.application.LocalDatabaseConnection;
import org.hos.application.LoggedInUser;
import org.hos.controller.LogInController;

import android.support.v7.app.ActionBarActivity;
import android.content.Context;
import android.content.Intent;
import android.content.pm.ActivityInfo;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.View.OnTouchListener;
import android.view.inputmethod.InputMethodManager;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;


public class MainActivity extends ActionBarActivity implements OnTouchListener, OnClickListener, Serializable
{
    SQLiteDatabase db;
    LogInController lc=new LogInController();
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        this.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
        View layout=findViewById(R.id.layout);
        layout.setOnTouchListener(this);
        Button login = (Button) findViewById(R.id.login); 
        login.setOnClickListener(this);
    }

    @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;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) 
    {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) 
        {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    @Override
    public boolean onTouch(View v, MotionEvent event) 
    {
        // TODO Auto-generated method stub
        InputMethodManager input = (InputMethodManager)getSystemService(Context.INPUT_METHOD_SERVICE);
        input.hideSoftInputFromWindow(getCurrentFocus().getWindowToken(), 0);
        return false;
    }

    @SuppressWarnings("static-access")
    @Override
    public void onClick(View v) 
    {
        EditText id=(EditText) findViewById(R.id.editText1);
        EditText password=(EditText) findViewById(R.id.editText2);
        String name = lc.login(id.getText().toString(), password.getText().toString(), this);
        //String name = conn.getUsername(id.getText().toString(), password.getText().toString());
        if(name!=null)
        {
            LoggedInUser user=new LoggedInUser();
            user.setUserId(name);
            user.setPrivilege(1);
            Intent intent = new Intent(this,LoggedInActivity.class);
            intent.putExtra("LoggedInUser",user);
            startActivity(intent);
            overridePendingTransition(R.anim.pull_in_right, R.anim.push_out_left);
        }
        else
            Toast.makeText(this, "Login invalid", Toast.LENGTH_SHORT).show();
    }
}

正如您可以看到onclick方法，具有loggedinuser对象的intent被传递给第二个activity。这个目标在下一个活动中收到。这是我的loggedinactivity.java：

package org.hos.view;

import org.hos.application.LoggedInUser;

import android.support.v7.app.ActionBarActivity;
import android.content.Intent;
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;

public class LoggedInActivity extends ActionBarActivity implements OnClickListener {

    Button logout;
    LoggedInUser user;
    @SuppressWarnings("static-access")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_logged_in);
        user = (LoggedInUser) getIntent().getExtras().getSerializable("LoggedInUser");
        setTitle("Hello "+user.getUserId());
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.logged_in, menu);
        //getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        logout=(Button) findViewById(R.id.logout);
        logout.setOnClickListener(this);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        else if(id == R.id.view_graph)
        {
            Intent intent = new Intent(this,ViewGraphActivity.class);
            intent.putExtra("LoggedInUser", user);
            startActivity(intent);
            overridePendingTransition(R.anim.pull_in_right, R.anim.push_out_left);
        }
        return super.onOptionsItemSelected(item);
    }

    public void onClick(View v)
    {
        if(v.equals(logout))
        {
            Intent intent=new Intent(this,MainActivity.class);
            intent.putExtra("LoggedInUSer", user);
            startActivity(intent);
            overridePendingTransition(R.anim.pull_in_left, R.anim.push_out_right);
        }
    }
}

因此，此活动再次连接了第三个活动，再次发送登录的用户对象。收到的方式是一样的。继承人我的观点graph.java：

package org.hos.view;

import org.hos.application.LoggedInUser;

import android.support.v4.app.NavUtils;
import android.support.v7.app.ActionBarActivity;
import android.content.Intent;
import android.content.pm.ActivityInfo;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;


public class ViewGraphActivity extends ActionBarActivity
{
    LoggedInUser user;
    @SuppressWarnings("static-access")
    @Override
    protected void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_view_graph);
        this.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
        user = (LoggedInUser) getIntent().getExtras().getSerializable("LoggedInUser");
        setTitle("Hello "+user.getUserId());
    }

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

    @Override
    public boolean onOptionsItemSelected(MenuItem item) 
    {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) 
        {
            return true;
        }
        else if(id == android.R.id.home)
        {
            Intent intent=new Intent(this,LoggedInActivity.class);
            intent.putExtra("LoggedInUser", user);
            overridePendingTransition(R.anim.pull_in_left, R.anim.push_out_right);
        }
        return super.onOptionsItemSelected(item);
    }
}

我的问题是第一次用户登录时，loggedinactivity.java会保存对象并传递给viewgraphactivity.java类。但是当从viewgraphactivity返回到loggedinactivity时，我得到以下异常：

11-07 13：53：39.258：E / AndroidRuntime（6165）：致命异常：主要 11-07 13：53：39.258：E / AndroidRuntime（6165）：java.lang.RuntimeException：无法启动＆gt;活动ComponentInfo {org.hos.view / org.hos.view.LoggedInActivity}：＆gt; java.lang .NullPointerException

为什么不能再使用viewgraphactivity发送的对象来记录活动？

谁能告诉我为什么会遇到这个问题？如果有任何解决方案。在此先感谢。

Answer 1

The only way to pass Custom object though intent is making it Serializable. Check the below link for more deatils

Person mPerson = new Person();  
mPerson.setName("Leon");  
mPerson.setAge(25);

Intent mIntent = new Intent(this,ObjectTranDemo1.class);   
Bundle mBundle = new Bundle();  
mBundle.putSerializable(SER_KEY,mPerson);  
mIntent.putExtras(mBundle);   

More details : http://www.easyinfogeek.com/2014/01/android-tutorial-two-methods-of-passing.html

第二次将对象从一个活动发送到另一个活动时出现异常

1 个答案: