Android 简明教程

Android - Navigation

在本章中，我们将看到如何提供在应用中向前和向后导航。首先，我们将了解如何在应用中提供向上导航。

In this chapter, we will see that how you can provide navigation forward and backward between an application. We will first look at how to provide up navigation in an application.

Providing Up Navigation

向上导航将允许我们的应用从下一个应用移动到前一个活动。它可以像这样进行。

The up navigation will allow our application to move to previous activity from the next activity. It can be done like this.

为了实现向上导航，第一步是声明哪些活动是每个活动的适当父级。你可以通过在活动中指定 parentActivityName 属性来完成此操作。其语法如下所示 −

To implement Up navigation, the first step is to declare which activity is the appropriate parent for each activity. You can do it by specifying parentActivityName attribute in an activity. Its syntax is given below −

android:parentActivityName = "com.example.test.MainActivity"

然后，你需要在活动 onCreate 方法中调用 setDisplayHomeAsUpEnabled 的 getActionBar() 方法。这将在顶部操作栏启用后退按钮。

After that you need to call setDisplayHomeAsUpEnabled method of getActionBar() in the onCreate method of the activity. This will enable the back button in the top action bar.

getActionBar().setDisplayHomeAsUpEnabled(true);

你最后需要做的事情是覆盖 onOptionsItemSelected 方法。当用户按它时，你的活动会接收对 onOptionsItemSelected() 的调用。该操作的 ID 为 android.R.id.home 。其语法如下所示 −

The last thing you need to do is to override onOptionsItemSelected method. when the user presses it, your activity receives a call to onOptionsItemSelected(). The ID for the action is android.R.id.home.Its syntax is given below −

public boolean onOptionsItemSelected(MenuItem item) {

   switch (item.getItemId()) {
      case android.R.id.home:
      NavUtils.navigateUpFromSameTask(this);
      return true;
   }
}

Handling device back button

由于你已启用后退按钮以在应用程序中导航，因此你可能希望在设备后退按钮中放入应用程序关闭功能。

Since you have enabled your back button to navigate within your application, you might want to put the application close function in the device back button.

可以通过覆盖 onBackPressed 以及调用 moveTaskToBack 和 finish 方法来实现此目的。其语法如下所示 −

It can be done by overriding onBackPressed and then calling moveTaskToBack and finish method. Its syntax is given below −

@Override
public void onBackPressed() {
   moveTaskToBack(true);
   MainActivity2.this.finish();
}

除了该 setDisplayHomeAsUpEnabled 方法，ActionBar API 类中还有其他方法。它们列在下面 −

Apart from this setDisplayHomeAsUpEnabled method, there are other methods available in ActionBar API class. They are listed below −

Sr.No

Method & description

1

addTab(ActionBar.Tab tab, boolean setSelected) This method adds a tab for use in tabbed navigation mode

2

getSelectedTab() This method returns the currently selected tab if in tabbed navigation mode and there is at least one tab present

3

hide() This method hide the ActionBar if it is currently showing

4

removeAllTabs() This method remove all tabs from the action bar and deselect the current tab

5

selectTab(ActionBar.Tab tab) This method select the specified tab

Example

下面的示例演示了如何使用导航。它创建了一个基本的应用程序，允许你在应用程序内导航。

The below example demonstrates the use of Navigation. It crates a basic application that allows you to navigate within your application.

要尝试本示例，您需要在实际设备或模拟器上运行它。

To experiment with this example, you need to run this on an actual device or in an emulator.

Steps

Description

1

You will use Android studio to create an Android application under a package com.example.sairamkrishna.myapplication.

2

Modify src/MainActivity.java file to add Activity code.

3

Create a new activity with the name of second_main.java and edit it to add activity code.

4

Modify layout XML file res/layout/activity_main.xml add any GUI component if required.

5

Modify layout XML file res/layout/second.xml add any GUI component if required.

6

Modify AndroidManifest.xml to add necessary code.

7

Run the application and choose a running android device and install the application on it and verify the results.

以下为 src/MainActivity.java 的内容。

Here is the content of src/MainActivity.java.

package com.example.sairamkrishna.myapplication;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends Activity  {
   Button b1;

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

      b1 = (Button) findViewById(R.id.button);
      b1.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View v) {
            Intent in=new Intent(MainActivity.this,second_main.class);
            startActivity(in);
         }
      });
   }
}

以下为 src/second_main.java 的内容。

Here is the content of src/second_main.java.

package com.example.sairamkrishna.myapplication;

import android.app.Activity;
import android.os.Bundle;
import android.webkit.WebView;
import android.webkit.WebViewClient;

/**
   * Created by Sairamkrishna on 4/6/2015.
*/

public class second_main extends Activity {
   WebView wv;

   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main_activity2);

      wv = (WebView) findViewById(R.id.webView);
      wv.setWebViewClient(new MyBrowser());
      wv.getSettings().setLoadsImagesAutomatically(true);
      wv.getSettings().setJavaScriptEnabled(true);
      wv.loadUrl("https://www.tutorialspoint.com");
   }

   private class MyBrowser extends WebViewClient {
      @Override
      public boolean shouldOverrideUrlLoading(WebView view, String url) {
         view.loadUrl(url);
         return true;
      }
   }
}

以下是 activity_main.xml 的内容。

Here is the content of activity_main.xml.

<?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: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"
   android:transitionGroup="true">

   <TextView android:text="Navigation example" android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:id="@+id/textview"
      android:textSize="35dp"
      android:layout_alignParentTop="true"
      android:layout_centerHorizontal="true" />

   <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Tutorials point"
      android:id="@+id/textView"
      android:layout_below="@+id/textview"
      android:layout_centerHorizontal="true"
      android:textColor="#ff7aff24"
      android:textSize="35dp" />

   <ImageView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:id="@+id/imageView"
      android:src="@drawable/abc"
      android:layout_below="@+id/textView"
      android:layout_centerHorizontal="true"
      android:theme="@style/Base.TextAppearance.AppCompat" />

   <Button
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="first page"
      android:id="@+id/button"
      android:layout_below="@+id/imageView"
      android:layout_alignRight="@+id/textView"
      android:layout_alignEnd="@+id/textView"
      android:layout_marginTop="61dp"
      android:layout_alignLeft="@+id/imageView"
      android:layout_alignStart="@+id/imageView" />

</RelativeLayout>

以下为 activity_main_activity2.xml 的内容。

Here is the content of activity_main_activity2.xml.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:orientation="vertical" android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:weightSum="1">

   <WebView
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:id="@+id/webView"
      android:layout_gravity="center_horizontal"
      android:layout_weight="1.03" />

</LinearLayout>

以下是 Strings.xml 的内容。

Here is the content of Strings.xml.

<resources>
   <string name="app_name">My Application</string>
</resources>

以下是 AndroidManifest.xml 的内容。

Here is the content of AndroidManifest.xml.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="com.example.sairamkrishna.myapplication" >
   <uses-permission android:name="android.permission.INTERNET"></uses-permission>

   <application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:theme="@style/AppTheme" >

      <activity
         android:name=".MainActivity"
         android:label="@string/app_name" >

         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>

      </activity>

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

   </application>
</manifest>

让我们尝试运行你的应用程序。我假设你在进行环境设置时已创建 AVD 。要从 Android Studio 运行应用程序，请打开项目的其中一个活动文件，然后单击工具栏中的运行图标。Android Studio 会将应用程序安装到你的 AVD 并启动它，如果你的设置和应用程序一切正常，它将显示以下模拟器窗口：

Let’s try to run your application. I assume you had created your AVD while doing environment setup. To run the app from Android studio, open one of your project’s activity files and click Run icon from the toolbar. Android studio installs the app on your AVD and starts it and if everything is fine with your setup and application, it will display following Emulator window−

现在只需按下按钮，将向你显示以下屏幕。

Now just press on button and the following screen will be shown to you.

navigation

第二个活动包含 webview，它已重新定向到 tutorialspoint.com，如下所示：

Second activity contains webview, it has redirected to tutorialspoint.com as shown below

navigation2