Android5.0开发范例大全 读书笔记（四），android5.0范例

Android5.0开发范例大全 读书笔记（四），android5.0范例

（三）通信和联网

3.1显示Web信息

1.WebView通过loadUrl()方法直接访问网页时，点击跳转链接会打开系统默认的浏览器，若要拦截WebView事件，可为其添加WebViewClient

webView.setWebViewClient(new WebViewClient())

2.WebView默认不支持JavaScript，要通过setJavaScriptEnabled()进行设置

 webView.getSettings().setJavaScriptEnabled(true);

3.WebView可以直接显示Html内容

3.4下载图片文件

1.自定义一个ImageView控件，实现资源的下载与显示

  值得一提的是，设置本地资源应该提供2个方法，一个通过资源id获取，一个通过drawable获取

  网络下载可以通过asynctask实现，要注意不要在doInBackground()中更新UI线程

  下面附上完整代码

public class WebImageView extends ImageView {
    private Drawable mPlaceholder, mImage;

    public WebImageView(Context context) {
        this(context, null);
    }

    public WebImageView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public WebImageView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    public void setPlaceholderImage(Drawable drawable) {
        mPlaceholder = drawable;
        if (mImage == null) {
            setImageDrawable(mPlaceholder);
        }
    }

    public void setPlaceholderImage(int resid) {
        mPlaceholder = getResources().getDrawable(resid);
        System.out.println(1);
        if (mImage == null) {
            System.out.println(2);
            setImageDrawable(mPlaceholder);
        }
    }

    public void setImageUrl(String url) {
        DownloadTask task = new DownloadTask();
        task.execute(url);
    }


    private class DownloadTask extends AsyncTask<String, Void, Bitmap> {

        @Override
        protected Bitmap doInBackground(String... params) {
            String url = params[0];
            try {
                URLConnection connection = (new URL(url)).openConnection();
                InputStream is = connection.getInputStream();
                return BitmapFactory.decodeStream(is);
            } catch (IOException e) {
                e.printStackTrace();
                return null;
            }
        }

        @Override
        protected void onPostExecute(Bitmap bitmap) {
            mImage = new BitmapDrawable(getContext().getResources(), bitmap);
            setImageDrawable(mImage);
        }
    }
}

3.5完全在后台下载

1.DownloadManager适合处理和管理需要长时间运行的下载操作。其优点是即使在下载失败，链接改变甚至设备重启时，依然会继续尝试下载

2.首先实现一个广播接收者来监听下载状态

 private BroadcastReceiver receiver=new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            queryDownloadStatus();
        }
    };

    private void queryDownloadStatus(){
        DownloadManager.Query query=new DownloadManager.Query();
        query.setFilterById(prefs.getLong(DL_ID,0));
        Cursor c=dm.query(query);
        if(c.moveToFirst()){
            int status=c.getInt(c.getColumnIndex(DownloadManager.COLUMN_STATUS));
            switch (status){
                case DownloadManager.STATUS_PAUSED:
                case DownloadManager.STATUS_PENDING:
                case DownloadManager.STATUS_RUNNING:
                    break;
                case DownloadManager.STATUS_SUCCESSFUL:
                    try {
                        ParcelFileDescriptor file=dm.openDownloadedFile(prefs.getLong(DL_ID,0));
                        FileInputStream fis=new ParcelFileDescriptor.AutoCloseInputStream(file);
                        imageView.setImageBitmap(BitmapFactory.decodeStream(fis));
                        Toast.makeText(this,"download over!",Toast.LENGTH_SHORT).show();
                    } catch (FileNotFoundException e) {
                        e.printStackTrace();
                    }
                    break;
                case DownloadManager.STATUS_FAILED:
                    dm.remove(prefs.getLong(DL_ID, 0));
                    prefs.edit().clear().apply();
                    break;
            }
        }
    }

3.接着获取系统服务

dm= (DownloadManager) getSystemService(DOWNLOAD_SERVICE);

4.最后，在onResume中注册广播并开始下载

 @Override
    protected void onResume() {
        super.onResume();
        if(!prefs.contains(DL_ID)){
            Uri resource=Uri.parse("http://f2.market.xiaomi.com/download/AppChannel/0965d34f016634cb83347f609306d9a3fa045a9c5/com.netease.onmyoji.mi.apk");
            DownloadManager.Request request=new DownloadManager.Request(resource);
            request.setAllowedNetworkTypes(DownloadManager.Request.NETWORK_MOBILE| DownloadManager.Request.NETWORK_WIFI);
            request.setTitle("Download Sample");
            request.setDescription("Download SSR!");
            request.setAllowedOverRoaming(false);
            long id=dm.enqueue(request);
            prefs.edit().putLong(DL_ID,id).apply();
        }else{
            queryDownloadStatus();
        }
        registerReceiver(receiver,new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE));
    }

3.10发送短信

1.与之前的DownloadManager一样，发送短信的SmsManager也是系统级服务，二者的调用极为相似

2..首先实现广播接收者，发送短信一共有2个接受者，一个返回发送是否成功

private BroadcastReceiver sent = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            switch (getResultCode()) {
                case Activity.RESULT_OK:
                    Toast.makeText(SendSmsActivity.this, "发送成功", Toast.LENGTH_SHORT).show();