Android Studio 3 教程之4-Activities

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内容：

Task 1. Create the TwoActivities project
Task 2. Create and launch the second activity
Task 3. Send data from the main activity to the second activity
Task 4. Return data back to the main activity

task1

Define the layout for the main activity

<?xml version="1.0" encoding="utf-8"?>
<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: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.android.twoactivities.MainActivity">
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/button_main"
android:id="@+id/button_main"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:onClick="launchSecondActivity"/>
</RelativeLayout>

Define the button action

Log.d(LOG_TAG, “Button clicked!”);

private static final String LOG_TAG = MainActivity.class.getSimpleName();

task2: Create and launch the second activity

Click the app folder for your project and choose File -> New -> Activity -> Empty Activity.
Modify the Android manifest

<activity android:name=".SecondActivity"></activity>

Add these attributes to the element:

android:label        "Second Activity"
android:parentActivityName     ".MainActivity"

Add a element inside the element for the second activity

<activity android:name=".SecondActivity"
   android:label="@string/activity2_name"
   android:parentActivityName=".MainActivity">
     <meta-data
        android:name="android.support.PARENT_ACTIVITY"
        android:value="com.example.android.twoactivities.MainActivity" />
</activity>

添加一个TextView,id设为“text_header”

<?xml version="1.0" encoding="utf-8"?>
<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: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=".SecondActivity">
<TextView
android:id="@+id/text_header"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="@dimen/activity_vertical_margin"
android:text="@string/text_header"
android:textAppearance="?android:attr/textAppearanceMedium"
android:textStyle="bold" />
</RelativeLayout>

在主activity中添加intent

Intent intent = new Intent(this, SecondActivity.class);

tartActivity(intent);

Task 3. Send data from the main activity to the second activity

Send data using intent

public static final String EXTRA_MESSAGE =
"com.example.android.twoactivities.extra.MESSAGE";


Intent intent = new Intent(this, SecondActivity.class);
String message = mMessageEditText.getText().toString();
intent.putExtra(EXTRA_MESSAGE, message);
startActivity(intent);

Add a TextView to the second activity for the message
get data from intent

Intent intent = getIntent();
String message =
intent.getStringExtra(MainActivity.EXTRA_MESSAGE);
TextView textView = (TextView) findViewById(R.id.text_message);
textView.setText(message);

Task 4. Return data back to the main activity

Add an EditText and a Button to the second activity layout
Create a response intent in the second activity

public static final String EXTRA_REPLY =
"com.example.android.twoactivities.extra.REPLY";

public void returnReply(View view) {
  String reply = mReply.getText().toString();
  Intent replyIntent = new Intent();
  replyIntent.putExtra(EXTRA_REPLY, reply);
  setResult(RESULT_OK, replyIntent);
  finish();
}

Add TextViews to the main activity layout to display the reply
Get the reply from the intent extra and display it

public static final int TEXT_REQUEST = 1;

startActivityForResult(intent, TEXT_REQUEST);

public void onActivityResult(int requestCode, int resultCode,
Intent data) {
  super.onActivityResult(requestCode, resultCode, data);
  if (requestCode == TEXT_REQUEST) {
    if (resultCode == RESULT_OK) {
      String reply =
      data.getStringExtra(SecondActivity.EXTRA_REPLY);
      mReplyHeadTextView.setVisibility(View.VISIBLE);
      mReplyTextView.setText(reply);
       mReplyTextView.setVisibility(View.VISIBLE);
    }
  }
}

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Android Studio 3 - Activities

内容：

task1

task2: Create and launch the second activity

Task 3. Send data from the main activity to the second activity

Task 4. Return data back to the main activity

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