需要幫助切換活動

Question

我在Android Studio上非常新，所以我要求初學者級別的解釋:)

我正在創建一個名為SyncZ的應用程序，我創建了一個登錄屏幕，我需要這樣做，以便當我按下“登錄或注冊”時，它會轉到我的activity_main.xml

我開始創建一個空白活動，然后添加了一個登錄活動，然后我將activity_login.xml設為main，以便在啟動應用程序時首先登錄菜單。

所以我真正的問題是，如何通過按鈕email_sign_in_button從我的activity_login切換到activity_main

這是我的代碼（XML和Java）如果文本太多，我很抱歉，我希望你能解決它:)

AndroidManifest.xml中

<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中

<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);
}
}

• 編輯 - 添加了Logcat Dropbox
• 編輯 - 更新了所有代碼。 通過LoginActivity.java中的logcat找到的錯誤（第177,151和82行）

錯誤行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 });

錯誤行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 }

錯誤行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

在您的登錄活動中編寫此代碼：這將從LoginActivity切換到MainActivity

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

Answer 2

在Android中，您可以使用Intent在“活動”之間切換。 您定義一個Intent，在激活時，將您的應用程序的用戶帶到另一個活動（稱為顯式Intent）。 您可以使用Intents在應用程序的活動之間傳遞信息（例如對象）。

簡而言之，如何使用Intent：

1. 實例化一個新的Intent，為它提供一個Context（通常是你當前的Activity）和目標Activity的類Object（MainActivity.class）
2. 如果您希望Intent將數據傳輸到新Activity，請使用其putExtra（）方法將數據附加到您的intent實例。 這基本上像地圖一樣工作。 您可以使用與存儲內容相同的密鑰來訪問目標Activity中的附加數據。
3. 在舊的Activity中調用startActivity（）
4. 在新的Activity（MainActivity）中，通過getStringExtra（）從Intent中提取數據

我在開始時發現誤導的一件事是android的活動生命周期和導航設施之間的聯系。 例如，您必須考慮在用戶按下按鈕時是否要啟動活動的新實例，或者是否要保留和重用實例等。

除了顯式Intents的基本導航功能之外，您還可以使用所謂的隱式Intent來提供對App獨立Android功能的訪問，例如寫一封電子郵件，......

這里有一個更深入的教程： http ： //developer.android.com/training/basics/firstapp/starting-activity.html

如果您想了解所有內容，請查看指向Google API Doc for Doc的鏈接： http ： //developer.android.com/reference/android/content/Intent.html

希望有所幫助。 馬庫斯

Answer 3

在活動之間移動的最佳方式通常是使用Intents（不確定您是否已經看過這些）。 有很多關於它們的資源，例如： http ： //www.vogella.com/tutorials/AndroidIntent/article.html 。 這個人有一些非常酷的初學者教程。 基本上會發生什么是在你的onClickListener方法中將傳遞一個意圖並啟動具有該意圖的活動。 意圖有助於跨活動獲取信息，盡管它們可用於各種很酷的內置任務，例如照片選擇。 我希望這有幫助。

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

以下代碼啟動活動：

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

但是，如果要將數據傳遞給MainActivity，則可以使用putExtra() ;

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