首先是欢迎界面的代码
public class WelcomeActivity extends Activity{
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.welcome);
/**
* 延迟3秒进入主界面
*/
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
Intent intent=new Intent(WelcomeActivity.this,LoginActivity.class);
startActivity(intent);
WelcomeActivity.this.finish();
}
},1000*3);
}
}
接下来是文章的主要内容。实现自动登录的关键是当程序从欢迎界面跳转到登录界面是，在登录界面还没有加载布局文件时判断是否登陆过，从而实现直接跳转到主界面。这里我们采用SharedPreferences来保存登录状态。代码如下：
public class LoginActivity extends Activity{
SharedPreferences sprfMain;
SharedPreferences.Editor editorMain;
Button login;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//在加载布局文件前判断是否登陆过
sprfMain= PreferenceManager.getDefaultSharedPreferences(this);
editorMain=sprfMain.edit();
//.getBoolean("main",false)；当找不到"main"所对应的键值是默认返回false
if(sprfMain.getBoolean("main",false)){
Intent intent=new Intent(LoginActivity.this,MainActivity.class);
startActivity(intent);
LoginActivity.this.finish();
}
setContentView(R.layout.login);
login= (Button) findViewById(R.id.login);
//这里只是简单用按键模拟登录功能
login.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent=new Intent(LoginActivity.this,MainActivity.class);
editorMain.putBoolean("main",true);
editorMain.commit();
startActivity(intent);
LoginActivity.this.finish();
}
});
}
}
接下来是实现注销后要重新进入登录界面
public class MainActivity extends AppCompatActivity {
SharedPreferences sprfMain;
SharedPreferences.Editor editorMain;
Button exit;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
exit= (Button) findViewById(R.id.exit);
exit.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//点击注销按键后调用LoginActivity提供的resetSprfMain()方法执行editorMain.putBoolean("main",false);，即将"main"对应的值修改为false
resetSprfMain();
Intent intent=new Intent(MainActivity.this,WelcomeActivity.class);
startActivity(intent);
MainActivity.this.finish();
}
});
}
public void resetSprfMain(){
sprfMain= PreferenceManager.getDefaultSharedPreferences(this);
editorMain=sprfMain.edit();
editorMain.putBoolean("main",false);
editorMain.commit();
}
}