需要帮助切换活动

Question

I'm VERY new at Android Studio so I ask kindly for an explanation on beginners level :)

I'm creating an app called SyncZ and I have a login screen created, I need to make it so that when I press 'Sign in or register' it goes to my activity_main.xml

I started by creating a blank activity and later added a login activity, I then made the activity_login.xml to be main so that the login menu would come first when starting the app.

So my real question is, how can I switch from my activity_login to activity_main with button email_sign_in_button

Here are my codes (XML and Java) I'm very sorry if it's too much text, I hope you can work it out :)

AndroidManifest.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context=".MainActivity">

<TextView
    android:text="@string/hello_world"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />

</RelativeLayout>

activity_login.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center_horizontal"
android:orientation="vertical"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.administrator.helloworld.LoginActivity"
>

<!-- Login progress -->
<ProgressBar
    android:id="@+id/login_progress"
    style="?android:attr/progressBarStyleLarge"
    android:layout_width="470dp"
    android:layout_height="470dp"
    android:layout_marginBottom="8dp"
    android:visibility="gone"/>

<LinearLayout
    android:id="@+id/email_login_form"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:weightSum="1">

    <ImageView
        android:layout_width="300dp"
        android:layout_height="160dp"
        android:id="@+id/imageView"
        android:layout_gravity="center_horizontal"
        android:background="@drawable/syncz"
        android:layout_marginTop="50dp"
        android:layout_marginBottom="75dp" />

    <TextView
        android:layout_width="79dp"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Login:"
        android:id="@+id/textView"
        android:textStyle="bold" />

    <AutoCompleteTextView
        android:id="@+id/email"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="@string/prompt_email"
        android:inputType="textEmailAddress"
        android:maxLines="1"
        android:singleLine="true"
        android:layout_marginTop="16dp"
        android:textStyle="italic"
        android:layout_marginBottom="10dp" />

    <EditText
        android:id="@+id/password"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Password"
        android:imeActionId="@+id/login"
        android:imeActionLabel="@string/action_sign_in_short"
        android:imeOptions="actionUnspecified"
        android:inputType="textPassword"
        android:maxLines="1"
        android:singleLine="true"
        android:textStyle="italic" />

    <Button
        android:id="@+id/email_sign_in_button"
        style="?android:textAppearanceSmall"
        android:layout_width="match_parent"
        android:layout_height="50dp"
        android:layout_marginTop="15dp"
        android:text="@string/action_sign_in"
        android:layout_weight="0.11"
        android:textSize="25dp"
        android:onClick="sendMessage" />/>
</LinearLayout>

</LinearLayout>

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context=".MainActivity">

<TextView
    android:text="@string/hello_world"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />

</RelativeLayout>

LoginActivity.java

package com.example.administrator.helloworld;
import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.annotation.TargetApi;
import android.app.Activity;
import android.app.LoaderManager.LoaderCallbacks;
import android.content.ContentResolver;
import android.content.CursorLoader;
import android.content.Intent;
import android.content.Loader;
import android.database.Cursor;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Build.VERSION;
import android.os.Build;
import android.os.Bundle;
import android.provider.ContactsContract;
import android.text.TextUtils;
import android.view.KeyEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.inputmethod.EditorInfo;
import android.widget.ArrayAdapter;
import android.widget.AutoCompleteTextView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import java.util.ArrayList;
import java.util.List;
/**
 * A login screen that offers login via email/password.
*/
public class LoginActivity extends Activity implements LoaderCallbacks<Cursor>{
/**
 * 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"
};
/**
 * Keep track of the login task to ensure we can cancel it if requested.
 */
private UserLoginTask mAuthTask = null;

// UI references.
private AutoCompleteTextView mEmailView;
private EditText mPasswordView;
private View mProgressView;
private View mLoginFormView;

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

    // Set up the login form.
    mEmailView = (AutoCompleteTextView) findViewById(R.id.email);
    populateAutoComplete();

    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;
        }
    });

    Button mEmailSignInButton = (Button) findViewById(R.id.email_sign_in_button);
    mEmailSignInButton.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View view) {
            attemptLogin();
            Intent intent= new Intent(LoginActivity.this,MainActivity.class);
            startActivity(intent);
        }
    });

    mLoginFormView = findViewById(R.id.login);
    mProgressView = findViewById(R.id.login_progress);
}

private void populateAutoComplete() {
    if (VERSION.SDK_INT >= 14) {
        // Use ContactsContract.Profile (API 14+)
        getLoaderManager().initLoader(0, null, this);
    } else if (VERSION.SDK_INT >= 9) {
        // Use AccountManager (API 8+)
        new SetupEmailAutoCompleteTask().execute(null, null);
    }
}



/**
 * 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.
    String email = mEmailView.getText().toString();
    String password = mPasswordView.getText().toString();

    boolean cancel = false;
    View focusView = null;


    // Check for a valid password, if the user entered one.
    if (!TextUtils.isEmpty(password) && !isPasswordValid(password)) {
        mPasswordView.setError(getString(R.string.error_invalid_password));
        focusView = mPasswordView;
        cancel = true;
    }

    // Check for a valid email address.
    if (TextUtils.isEmpty(email)) {
        mEmailView.setError(getString(R.string.error_field_required));
        focusView = mEmailView;
        cancel = true;
    } else if (!isEmailValid(email)) {
        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.
        showProgress(true);
        mAuthTask = new UserLoginTask(email, password);
        mAuthTask.execute((Void) null);
    }
}
private boolean isEmailValid(String email) {
    //TODO: Replace this with your own logic
    return email.contains("@");
}

private boolean isPasswordValid(String password) {
    //TODO: Replace this with your own logic
    return password.length() > 4;
}

/**
 * Shows the progress UI and hides the login form.
 */
@TargetApi(Build.VERSION_CODES.HONEYCOMB_MR2)
public 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);

        mLoginFormView.setVisibility(show ? View.GONE : 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);
            }
        });

        mProgressView.setVisibility(show ? View.VISIBLE : View.GONE);
        mProgressView.animate().setDuration(shortAnimTime).alpha(
                show ? 1 : 0).setListener(new AnimatorListenerAdapter() {
            @Override
            public void onAnimationEnd(Animator animation) {
                mProgressView.setVisibility(show ? View.VISIBLE : View.GONE);
            }
        });
    } else {
        // The ViewPropertyAnimator APIs are not available, so simply show
        // and hide the relevant UI components.
        mProgressView.setVisibility(show ? View.VISIBLE : View.GONE);
        mLoginFormView.setVisibility(show ? View.GONE : View.VISIBLE);
    }
}

@Override
public Loader<Cursor> onCreateLoader(int i, Bundle bundle) {
    return new CursorLoader(this,
            // Retrieve data rows for the device user's 'profile' contact.
            Uri.withAppendedPath(ContactsContract.Profile.CONTENT_URI,
                    ContactsContract.Contacts.Data.CONTENT_DIRECTORY), ProfileQuery.PROJECTION,

            // Select only email addresses.
            ContactsContract.Contacts.Data.MIMETYPE +
                    " = ?", new String[]{ContactsContract.CommonDataKinds.Email
                                                                 .CONTENT_ITEM_TYPE},

            // Show primary email addresses first. Note that there won't be
            // a primary email address if the user hasn't specified one.
            ContactsContract.Contacts.Data.IS_PRIMARY + " DESC");
}

@Override
public void onLoadFinished(Loader<Cursor> cursorLoader, Cursor cursor) {
    List<String> emails = new ArrayList<String>();
    cursor.moveToFirst();
    while (!cursor.isAfterLast()) {
        emails.add(cursor.getString(ProfileQuery.ADDRESS));
        cursor.moveToNext();
    }

    addEmailsToAutoComplete(emails);
}

@Override
public void onLoaderReset(Loader<Cursor> cursorLoader) {

}

private interface ProfileQuery {
    String[] PROJECTION = {
            ContactsContract.CommonDataKinds.Email.ADDRESS,
            ContactsContract.CommonDataKinds.Email.IS_PRIMARY,
    };

    int ADDRESS = 0;
    int IS_PRIMARY = 1;
}

/**
 * Use an AsyncTask to fetch the user's email addresses on a background thread, and update
 * the email text field with results on the main UI thread.
 */
class SetupEmailAutoCompleteTask extends AsyncTask<Void, Void, List<String>> {

    @Override
    protected List<String> doInBackground(Void... voids) {
        ArrayList<String> emailAddressCollection = new ArrayList<String>();

        // Get all emails from the user's contacts and copy them to a list.
        ContentResolver cr = getContentResolver();
        Cursor emailCur = cr.query(ContactsContract.CommonDataKinds.Email.CONTENT_URI, null,
                null, null, null);
        while (emailCur.moveToNext()) {
            String email = emailCur.getString(emailCur.getColumnIndex(ContactsContract
                    .CommonDataKinds.Email.DATA));
            emailAddressCollection.add(email);
        }
        emailCur.close();

        return emailAddressCollection;
    }

    @Override
    protected void onPostExecute(List<String> emailAddressCollection) {
       addEmailsToAutoComplete(emailAddressCollection);
    }
}

private void addEmailsToAutoComplete(List<String> emailAddressCollection) {
    //Create adapter to tell the AutoCompleteTextView what to show in its dropdown list.
    ArrayAdapter<String> adapter =
            new ArrayAdapter<String>(LoginActivity.this,
                    android.R.layout.simple_dropdown_item_1line, emailAddressCollection);

    mEmailView.setAdapter(adapter);
}

/**
 * Represents an asynchronous login/registration task used to authenticate
 * the user.
 */
public class UserLoginTask extends AsyncTask<Void, Void, Boolean> {

    private final String mEmail;
    private final String mPassword;

    UserLoginTask(String email, String password) {
        mEmail = email;
        mPassword = password;
    }

    @Override
    protected Boolean doInBackground(Void... params) {
        // TODO: attempt authentication against a network service.

        try {
            // Simulate network access.
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            return false;
        }

        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);

        if (success) {
            finish();
        } else {
            mPasswordView.setError(getString(R.string.error_incorrect_password));
            mPasswordView.requestFocus();
        }
    }

    @Override
    protected void onCancelled() {
        mAuthTask = null;
        showProgress(false);
    }
}
}

MainActivity.java

package com.example.administrator.helloworld;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends ActionBarActivity {

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


@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);
}
}

• Edit - Added Logcat Dropbox
• Edit - Updated all codes. Errors found via logcat in LoginActivity.java (line 177, 151 and 82)

Error line 82:

78 Button mEmailSignInButton = (Button) findViewById(R.id.email_sign_in_button);
79   mEmailSignInButton.setOnClickListener(new OnClickListener() {
80      @Override
81      public void onClick(View view) {
82          attemptLogin();
83          Intent intent= new Intent(LoginActivity.this,MainActivity.class);
84          startActivity(intent);
85      }
86 });

Error line 151:

144 if (cancel) {
145     // There was an error; don't attempt login and focus the first
146     // form field with an error.
147     focusView.requestFocus();
148 } else {
149     // Show a progress spinner, and kick off a background task to
150     // perform the user login attempt.
151     showProgress(true);
152     mAuthTask = new UserLoginTask(email, password);
153     mAuthTask.execute((Void) null);
154 }

Error line 177:

177 mLoginFormView.setVisibility(show ? View.GONE : View.VISIBLE);
178     mLoginFormView.animate().setDuration(shortAnimTime).alpha(
179             show ? 0 : 1).setListener(new AnimatorListenerAdapter() {
180         @Override
181         public void onAnimationEnd(Animator animation) {
182             mLoginFormView.setVisibility(show ? View.GONE : View.VISIBLE);
183         }
184 });

Answer 1

In your login activity write this code: this will switch from LoginActivity to MainActivity

startActivity(new Intent(LoginActivity.this, MainActivity.class));
finish();

Answer 2

in Android you can switch between Activities using Intent's. You define an Intent that, when activated, takes the user of your app to another activity (called an explicit Intent). You can use Intents to pass Information (eg Objects) between the Activities of you app.

In a nutshell, how to use an Intent:

1. Instantiate a new Intent providing it with a Context (usually your current Activity this) and the class Object of the target Activity (MainActivity.class)
2. If you want the Intent to transport Data to your new Activity attach the data to your intent instance using its putExtra() Methods. This basically works like a Map. You can access the attached data in your target Activity using the same key that you stored the stuff with in the first place.
3. Call startActivity() in your old Activity
4. In your new Activity (MainActivity) extract the data from your Intent by getStringExtra()

One thing I found misleading when starting out was the connection between the android's activity lifecycle and the navigational facilities. Eg you have to think about whether you want to start new instances of your activities when the user presses the button or whether you want to keep and reuse instances, etc.

In addition to the basic navigational features of explicit Intents you can also use so called implicit Intents to provide access to App independent Android functionality eg write an email,...

A more in depth tutorial is found here: http://developer.android.com/training/basics/firstapp/starting-activity.html

If you want to know it all check this link to the Google API Doc for Intents: http://developer.android.com/reference/android/content/Intent.html

Hope that helps. Markus

Answer 3

The best way to move between activities is usually using Intents (not sure if you have seen these). There are plenty resources regarding them such as this one: http://www.vogella.com/tutorials/AndroidIntent/article.html . This guy has some really cool tutorials for beginners. Basically what will happen is in your onClickListener method will pass an intent and start an activity with that intent. The intent helps take info across activities, although they can be used for a variety of cool built in tasks as well such as photo selection. I hope this helps.

Answer 4

 Button mEmailSignInButton = (Button) findViewById(R.id.email_sign_in_button);
mEmailSignInButton.setOnClickListener(new OnClickListener() {
    @Override
    public void onClick(View view) {
        Intent intent= new Intent(LoginActivity.this,MainActivity.class);
        startActivity(intent);
    }
});

Answer 5

The following code starts the activity:

Intent intent = new Intent(LoginActivity.this, MainActivity.class);
startaActivity(intent);

However, if you are going to pass data to MainActivity, you can use putExtra() ;

Intent intent = new Intent(LoginActivity.this, MainActivity.class);
intent.putExtra("myData", the data here);
startActivity(intent);