我是 Android 开发新手，在与 AppInventor 短暂接触后正在使用 Android Studio。
我已经阅读了开始一项活动并获取结果以及检查示例的内容。
在我的 MainActivity 上，我有一个登录按钮，用于启动 LoginActivity。例如，我将调用活动（MainActivity）的“额外”传递给被调用的活动（LoginActivity），如下所示，并在返回时（它实际上并没有在任何地方登录）它设置了两个应该是的额外参数传回 MainActivity：
我的 LoginActivity 是由 New Activity Wizard 创建的模板的略微修改版本。基本上我定义了 OUTPARAM 静态字符串（额外参数的名称）并添加了代码来读取传入参数并设置传出参数：
package com.example.testapp.ui;
import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.annotation.TargetApi;
import android.app.Activity;
import android.os.AsyncTask;
import android.os.Build;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.KeyEvent;
import android.view.Menu;
import android.view.View;
import android.view.inputmethod.EditorInfo;
import android.widget.EditText;
import android.widget.TextView;
import android.view.MenuItem;
import android.support.v4.app.NavUtils;
/**
* Activity which displays a login screen to the user, offering registration as
* well.
*/
public class LoginActivity extends Activity {
// DEGT : Activity parameters passed via intent.putExtra
static public final String INPARAM_METHOD = "com.example.testapp.ui.loginMethod";
static public final String OUTPARAM_USERID = "com.example.testapp.ui.userId";
static public final String OUTPARAM_PASSW = "com.example.testapp.ui.password";
/**
* A dummy authentication store containing known user names and passwords.
* TODO: remove after connecting to a real authentication system.
*/
private static final String[] DUMMY_CREDENTIALS = new String[]{
"foo@example.com:hello",
"bar@example.com:world"
};
/**
* The default email to populate the email field with.
*/
public static final String EXTRA_EMAIL = "com.example.android.authenticatordemo.extra.EMAIL";
/**
* Keep track of the login task to ensure we can cancel it if requested.
*/
private UserLoginTask mAuthTask = null;
// Values for email and password at the time of the login attempt.
private String mEmail;
private String mPassword;
// UI references.
private EditText mEmailView;
private EditText mPasswordView;
private View mLoginFormView;
private View mLoginStatusView;
private TextView mLoginStatusMessageView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
setupActionBar();
// Set up the login form.
mEmail = getIntent().getStringExtra(EXTRA_EMAIL); // TODO modify
mEmailView = (EditText) findViewById(R.id.email);
mEmailView.setText(mEmail);
mPasswordView = (EditText) findViewById(R.id.password);
mPasswordView.setOnEditorActionListener(new TextView.OnEditorActionListener() {
@Override
public boolean onEditorAction(TextView textView, int id, KeyEvent keyEvent) {
if (id == R.id.login || id == EditorInfo.IME_NULL) {
attemptLogin();
return true;
}
return false;
}
});
mLoginFormView = findViewById(R.id.login_form);
mLoginStatusView = findViewById(R.id.login_status);
mLoginStatusMessageView = (TextView) findViewById(R.id.login_status_message);
findViewById(R.id.sign_in_button).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
attemptLogin();
}
});
}
/**
* Set up the {@link android.app.ActionBar}, if the API is available.
*/
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
private void setupActionBar() {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
// Show the Up button in the action bar.
getActionBar().setDisplayHomeAsUpEnabled(true);
}
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
// This ID represents the Home or Up button. In the case of this
// activity, the Up button is shown. Use NavUtils to allow users
// to navigate up one level in the application structure. For
// more details, see the Navigation pattern on Android Design:
//
// http://developer.android.com/design/patterns/navigation.html#up-vs-back
//
// TODO: If Settings has multiple levels, Up should navigate up
// that hierarchy.
NavUtils.navigateUpFromSameTask(this);
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
super.onCreateOptionsMenu(menu);
getMenuInflater().inflate(R.menu.login, menu);
return true;
}
/**
* Attempts to sign in or register the account specified by the login form.
* If there are form errors (invalid email, missing fields, etc.), the
* errors are presented and no actual login attempt is made.
*/
public void attemptLogin() {
if (mAuthTask != null) {
return;
}
// Reset errors.
mEmailView.setError(null);
mPasswordView.setError(null);
// Store values at the time of the login attempt.
mEmail = mEmailView.getText().toString();
mPassword = mPasswordView.getText().toString();
boolean cancel = false;
View focusView = null;
// Check for a valid password.
if (TextUtils.isEmpty(mPassword)) {
mPasswordView.setError(getString(R.string.error_field_required));
focusView = mPasswordView;
cancel = true;
} else if (mPassword.length() < 4) {
mPasswordView.setError(getString(R.string.error_invalid_password));
focusView = mPasswordView;
cancel = true;
}
// Check for a valid email address.
if (TextUtils.isEmpty(mEmail)) {
mEmailView.setError(getString(R.string.error_field_required));
focusView = mEmailView;
cancel = true;
} else if (!mEmail.contains("@")) {
mEmailView.setError(getString(R.string.error_invalid_email));
focusView = mEmailView;
cancel = true;
}
if (cancel) {
// There was an error; don't attempt login and focus the first
// form field with an error.
focusView.requestFocus();
} else {
// Show a progress spinner, and kick off a background task to
// perform the user login attempt.
mLoginStatusMessageView.setText(R.string.login_progress_signing_in);
showProgress(true);
mAuthTask = new UserLoginTask();
mAuthTask.execute((Void) null);
}
}
/**
* Shows the progress UI and hides the login form.
*/
@TargetApi(Build.VERSION_CODES.HONEYCOMB_MR2)
private void showProgress(final boolean show) {
// On Honeycomb MR2 we have the ViewPropertyAnimator APIs, which allow
// for very easy animations. If available, use these APIs to fade-in
// the progress spinner.
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB_MR2) {
int shortAnimTime = getResources().getInteger(android.R.integer.config_shortAnimTime);
mLoginStatusView.setVisibility(View.VISIBLE);
mLoginStatusView.animate()
.setDuration(shortAnimTime)
.alpha(show ? 1 : 0)
.setListener(new AnimatorListenerAdapter() {
@Override
public void onAnimationEnd(Animator animation) {
mLoginStatusView.setVisibility(show ? View.VISIBLE : View.GONE);
}
});
mLoginFormView.setVisibility(View.VISIBLE);
mLoginFormView.animate()
.setDuration(shortAnimTime)
.alpha(show ? 0 : 1)
.setListener(new AnimatorListenerAdapter() {
@Override
public void onAnimationEnd(Animator animation) {
mLoginFormView.setVisibility(show ? View.GONE : View.VISIBLE);
}
});
} else {
// The ViewPropertyAnimator APIs are not available, so simply show
// and hide the relevant UI components.
mLoginStatusView.setVisibility(show ? View.VISIBLE : View.GONE);
mLoginFormView.setVisibility(show ? View.GONE : View.VISIBLE);
}
}
/**
* Represents an asynchronous login/registration task used to authenticate
* the user.
*/
public class UserLoginTask extends AsyncTask<Void, Void, Boolean> {
@Override
protected Boolean doInBackground(Void... params) {
// TODO: attempt authentication against a network service.
try {
// Simulate network access.
Thread.sleep(2000);
// TODO DEGT
// 1. Use Server setting to select Login Service URL
// 2. Download list of exhibition rooms to populate spinner on MainActivity
} catch (InterruptedException e) {
return false;
}
// get the intent extras (parameters passed to activity)
android.content.Intent intent = getIntent();
if (intent.getStringExtra(LoginActivity.INPARAM_METHOD).equalsIgnoreCase("manual"))
{
for (String credential : DUMMY_CREDENTIALS) {
String[] pieces = credential.split(":");
if (pieces[0].equals(mEmail)) {
// Account exists, return true if the password matches.
return pieces[1].equals(mPassword);
}
}
}
// TODO: register the new account here.
return true;
}
@Override
protected void onPostExecute(final Boolean success) {
mAuthTask = null;
showProgress(false);
// get the intent extras passed to the activity by calling activity
android.content.Intent intent = getIntent();
if (success) {
// TO-TEST pass the credentials back to the calling activity
intent.putExtra(OUTPARAM_USERID, mEmailView.getText());
intent.putExtra(OUTPARAM_PASSW, mPasswordView.getText());
setResult(RESULT_OK, intent); // otherwise it returns RESULT_CANCELED
setIntent(intent);
finish();
} else {
// TO-TEST pass the credentials back to the calling activity
intent.putExtra(OUTPARAM_USERID, "");
intent.putExtra(OUTPARAM_PASSW, "");
setIntent(intent);
mPasswordView.setError(getString(R.string.error_incorrect_password));
mPasswordView.requestFocus();
}
}
@Override
protected void onCancelled() {
mAuthTask = null;
showProgress(false);
}
}
}
在 UserLoginTask 类（在 LoginActivity 类中定义）中，我检查了 doInBackground() 方法的输入参数 (INPARAM_*)。调试断点表明我得到了 MainActivity 设置的正确值。
在 onPostExecute() 方法上，我设置了两个 OUTPARAM 附加功能。在调试期间，我确认这些值实际上已插入 Intent 的 Bundle 中。但是，当控制权传回（调用）MainActivity时，onActivityResult方法的data参数中传入的Intent中的所有参数（INPARAM、OUTPARAM）都是不存在的：
（调用）MainActivity 如下：
package com.example.testapp.ui;
import android.os.Bundle;
import android.app.Activity;
import android.provider.ContactsContract;
import android.view.Menu;
import android.widget.Button; // Button
import android.view.View; // View
import android.content.Intent; // Intent
import android.widget.TextView;
public class MainActivity extends Activity {
static public final int AUTHENTICATE_TICKET = 2; // Login to server
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Create the Login button onClick to start LoginActivity
Button button= (Button) findViewById(R.id.buttonLogin);
button.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
//startActivity(new Intent(MainActivity.this, LoginActivity.class));
Intent intent = new Intent(MainActivity.this, LoginActivity.class);
intent.putExtra(LoginActivity.INPARAM_METHOD, "manual"); // DEGT dummy for now
startActivityForResult(intent, AUTHENTICATE_TICKET);
}
});
}
@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
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
// Check which request we're responding to
if (requestCode == AUTHENTICATE_TICKET)
{ // Successful LoginActivity result.
if (resultCode == RESULT_OK)
{
// Get a reference to the TextView we will update
final TextView txtMainMessage = (TextView)findViewById(R.id.textViewMainMessage);
// Update the TextView with a personalized message. TODO Localize
String userId = data.getExtras().getString(LoginActivity.OUTPARAM_USERID);
String msg = "Hello " + userId + ". Now select the exhibition room please.";
txtMainMessage.setText(msg);
}
}
}
}
