[移动开发]安卓实现浏览器app

安卓给app提供了：

WebView：可以显示网页的组件，详见谷歌WebView文档

借助安卓的WebView，我们可以轻松的实现一个浏览器app。首先来看我们的布局文件activity_web.xml：

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.sc.web.WebActivity">

    <com.google.android.material.appbar.AppBarLayout
        android:focusableInTouchMode="true"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <androidx.appcompat.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
            app:layout_scrollFlags="scroll|enterAlways|snap">

            <EditText
                android:id="@+id/url_edit_text"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:inputType="textUri"/>

        </androidx.appcompat.widget.Toolbar>

    </com.google.android.material.appbar.AppBarLayout>

    <WebView
        android:id="@+id/web_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />

</androidx.coordinatorlayout.widget.CoordinatorLayout>

界面上的主角就是我们的WebView，这里除了WebView，我们还使用了Toolbar来显示我们的网页链接，并提供网页跳转、前进、后退按钮。

接下来实现WebActivity：

class WebActivity : AppCompatActivity() {
    private lateinit var mWebView: WebView

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_web)

        val toolbar = findViewById<Toolbar>(R.id.toolbar)
        setSupportActionBar(toolbar)
        supportActionBar?.apply {
            setDisplayHomeAsUpEnabled(true)
            setHomeAsUpIndicator(R.mipmap.ic_x)
            setDisplayShowTitleEnabled(false)
        }

        val urlEditText = findViewById<EditText>(R.id.url_edit_text)
        mWebView = findViewById(R.id.web_view)
        mWebView.settings.javaScriptEnabled = true
        mWebView.webViewClient = object : WebViewClient() {
            override fun onPageStarted(view: WebView, url: String, favicon: Bitmap?) {
                super.onPageStarted(view, url, favicon)
                urlEditText.setText(url)
            }
            override fun onPageFinished(view: WebView, url: String) {  // 这个也必须要，否则有时url不能正确显示
                super.onPageFinished(view, url)
                urlEditText.setText(url)
            }
        }

        val uri = intent.data
        if (uri == null) {  // 未指定url则默认进入百度页面
            mWebView.loadUrl("https://www.baidu.com/")
        } else {  // 进入指定的url页面
            mWebView.loadUrl(uri.toString())
        }

        val inputMethodManager = getSystemService(INPUT_METHOD_SERVICE) as InputMethodManager
        // 点击WebView时隐藏输入法并取消对urlEditText的焦距
        mWebView.setOnTouchListener { v, event ->
            inputMethodManager.hideSoftInputFromWindow(urlEditText.applicationWindowToken, 0)
            urlEditText.clearFocus()
            false
        }
        // 点击输入法上的确认时隐藏输入法并跳转网页
        urlEditText.setOnEditorActionListener { textView, i, keyEvent ->
            inputMethodManager.hideSoftInputFromWindow(textView.applicationWindowToken, 0)
            mWebView.loadUrl(urlEditText.text.toString())
            false
        }
        // 处理点击下载文件的情况
        mWebView.setDownloadListener { url, userAgent, contentDisposition, mimetype, contentLength ->
            this@WebActivity.url = url
            this@WebActivity.contentLength = contentLength
            if (ContextCompat.checkSelfPermission(this@WebActivity, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
                ActivityCompat.requestPermissions(this@WebActivity, arrayOf(Manifest.permission.WRITE_EXTERNAL_STORAGE), REQUEST_CODE_DOWNLAOD)
            } else {
                download()
            }
        }
    }

    private var url: String? = null
    private var contentLength: Long = 0

    private fun download() {
        val intent = Intent(this, DownloadService::class.java)
        startService(intent)
        bindService(intent, object : ServiceConnection {
            override fun onServiceConnected(name: ComponentName, service: IBinder) {
                val downloadBinder = service as DownloadBinder
                downloadBinder.startDownload(url!!, contentLength)
                unbindService(this)
            }
            override fun onServiceDisconnected(name: ComponentName) { }
        }, BIND_AUTO_CREATE)
    }

    override fun onRequestPermissionsResult(requestCode: Int, permissions: Array<String>, grantResults: IntArray) {
        when (requestCode) {
            REQUEST_CODE_DOWNLAOD -> if (grantResults.isNotEmpty() && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                download()
            } else {
                Toast.makeText(this, "You denied the permission", Toast.LENGTH_SHORT).show()
            }
        }
    }

    override fun onCreateOptionsMenu(menu: Menu): Boolean {
        menuInflater.inflate(R.menu.toolbar_web, menu)
        return true
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        when (item.itemId) {
            android.R.id.home -> finish()
            R.id.refresh -> mWebView.reload()
            R.id.go_back -> mWebView.goBack()
            R.id.go_forward -> mWebView.goForward()
        }
        return true
    }

    override fun onBackPressed() {
        if (mWebView.canGoBack()) {
            mWebView.goBack()
        } else {
            finish()
        }
    }

    companion object {

        private const val REQUEST_CODE_DOWNLAOD = 1

        fun actionStart(context: Context) {
            val intent = Intent(context, WebActivity::class.java)
            context.startActivity(intent)
        }
    }
}

在onCreate中首先调用WebView的loadUrl方法进入指定的url或者，如果Activity启动时没有指定url，则进入百度页面。

如果希望其它app要打开浏览器显示指定url时可以跳转到我们的浏览器，可以在AndroidManifest.xml中为我们的WebActivity加上intent-filter：

        <activity
            android:name="com.sc.web.WebActivity"
            android:icon="@drawable/ic_web"
            android:label="@string/web"
            android:launchMode="singleTask"
            android:taskAffinity="com.sc.web"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.VIEW" />

                <category android:name="android.intent.category.DEFAULT" />
                <category android:name="android.intent.category.BROWSABLE" />

                <data android:scheme="http" />
                <data android:scheme="https" />
            </intent-filter>
        </activity>

就这样实现了一个简单的浏览器app。

源代码地址：https://github.com/SSSxCCC/SCApp

总结

安卓借助WebView可以轻松实现一个浏览器