16 tips for Android development

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1. The return value of getTextSize in TextView is in pixels (px).

The unit of setTextSize() is sp.

So if you use the returned value directly to set it, it will go wrong. The solution is to use another form of setTextSize(), which can specify the unit:

 <span style= "font-size:16px;" >setTextSize( int unit, int size)
 TypedValue.COMPLEX_UNIT_PX : Pixels
 TypedValue.COMPLEX_UNIT_SP : Scaled Pixels
 TypedValue.COMPLEX_UNIT_DIP : Device Independent Pixels</span>

2. When inheriting from View, when drawing the bitmap, you need to put the image into the newly created drawable-xdpi

Otherwise, the drawing size may change easily.

3. Underline the text: textView.getPaint().setFlags(Paint.STRIKE_THRU_TEXT_FLAG);

4. ScrollView inherits from frameLayout, so you need to use frameLayout when using LayoutParams.

5. Several ways of network programming in Android:
(1) Socket and ServerSocket for TCP/IP
(2) DatagramSocket and DatagramPackage for UDP. It should be noted that, considering that Android devices are usually handheld terminals, IP addresses are assigned as they go online. They are not fixed. Therefore, the development is somewhat different from ordinary Internet applications.
(3) HttpURLConnection for direct URLs
(4) Google has integrated the Apache HTTP client, and HTTP can be used for network programming. For HTTP, Google has integrated Appache Http core and httpclient 4. Therefore, please note that Android does not support the httpclient 3.x series, and currently does not support Multipart (MIME). You need to add httpmime.jar yourself.
(5) Use Web Service. Android can support Xmlrpc and Jsonrpc through open source packages such as jackson. You can also use Ksoap2 to implement Web service.
(6) Use the WebView component to display web pages directly. Based on WebView, Google has provided a web browser based on chrome-lite, which can be used to browse the web directly.

6. TranslateAnimation(float fromXDelta, float toXDelta, float fromYDelta, float toYDelta)

This is the construction method we use most often.

float fromXDelta: This parameter indicates the difference between the point where the animation starts and the current View X coordinate;

float toXDelta, this parameter indicates the difference between the end point of the animation and the current View X coordinate;

float fromYDelta, this parameter indicates the difference between the animation start point and the current View Y coordinate;

float toYDelta) This parameter represents the difference between the point where the animation starts and the Y coordinate of the current View;

If the view is at point A (x, y), then the animation moves from point B (x+fromXDelta, y+fromYDelta) to point C (x+toXDelta, y+toYDelta).

7.Android provides several ways to access the UI thread from other threads.
Activity.runOnUiThread( Runnable )
View.post( Runnable )
View.postDelayed( Runnable, long )
Hanlder

AsyncTask (recommended)

 Get a web page from the Internet and display its source code in a TextView
 package org.unique.async;
 import java.io.ByteArrayOutputStream;
 import java.io.InputStream;
 import java.util.ArrayList; 
   
 import org.apache.http.HttpEntity;
 import org.apache.http.HttpResponse;
 import org.apache.http.client.HttpClient;
 import org.apache.http.client.methods.HttpGet;
 import org.apache.http.impl.client.DefaultHttpClient; 
   
 import android.app.Activity;
 import android.app.ProgressDialog;
 import android.content.Context;
 import android.content.DialogInterface;
 import android.os.AsyncTask;
 import android.os.Bundle;
 import android.os.Handler;
 import android.os.Message;
 import android.view.View;
 import android.widget.Button;
 import android.widget.EditText;
 import android.widget.TextView; 
   
 public   class NetworkActivity extends Activity{
 private TextView message;
 private Button open;
 private EditText url; 
   
 @Override    
 public   void onCreate(Bundle savedInstanceState) {
 super .onCreate(savedInstanceState);
       setContentView(R.layout.network);
       message= (TextView) findViewById(R.id.message);
       url= (EditText) findViewById(R.id.url);
       open= (Button) findViewById(R.id.open);
       open.setOnClickListener( new View.OnClickListener() {
 public   void onClick(View arg0) {
 connect();
 }
 }); 
   
 } 
   
 private   void connect() {
        PageTask task = new PageTask( this );
        task.execute(url.getText().toString());
 } 
   
 class PageTask extends AsyncTask<String, Integer, String> {
 // Variable-length input parameters, corresponding to AsyncTask.exucute()  
        ProgressDialog pdialog;
 public PageTask(Context context){
            pdialog = new ProgressDialog(context, 0 );
            pdialog.setButton( "cancel" , new DialogInterface.OnClickListener() {
 public   void onClick(DialogInterface dialog, int i) {
              dialog.cancel();
 }
 });
            pdialog.setOnCancelListener( new DialogInterface.OnCancelListener() {
 public   void onCancel(DialogInterface dialog) {
 finish();
 }
 });
            pdialog.setCancelable( true );
            pdialog.setMax( 100 );
            pdialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
 pdialog.show(); 
   
 }
 @Override    
 protected String doInBackground(String... params) { 
   
 try { 
   
               HttpClient client = new DefaultHttpClient();
 // params[0] represents the URL of the connection  
               HttpGet get = new HttpGet(params[ 0 ]);
               HttpResponse response = client.execute(get);
               HttpEntity entity = response.getEntity();
 long length = entity.getContentLength();
               InputStream is = entity.getContent();
               String s = null ;
 if (is != null ) {
                   ByteArrayOutputStream baos = new ByteArrayOutputStream(); 
   
 byte [] buf = new   byte [ 128 ]; 
   
 int ch = - 1 ; 
   
 int count = 0 ; 
   
 while ((ch = is.read(buf)) != - 1 ) { 
   
                      baos.write(buf, 0 , ch); 
   
                      count += ch; 
   
 if (length > 0 ) {
 // If you know the length of the response, call publishProgress() to update the progress  
                          publishProgress(( int ) ((count / ( float ) length) * 100 ));
 } 
   
 // Let the thread sleep for 100ms  
                      Thread.sleep( 100 );
 }
                   s = new String(baos.toByteArray()); }
 // Return result  
 return s;
            } catch (Exception e) {
               e.printStackTrace(); 
   
 } 
   
 return   null ; 
   
 } 
   
 @Override    
 protected   void onCancelled() {
 super .onCancelled();
 } 
   
 @Override    
 protected   void onPostExecute(String result) {
 // Return the content of the HTML page  
            message.setText(result);
            pdialog.dismiss();
 } 
   
 @Override    
 protected   void onPreExecute() {
 // Task starts, you can display a dialog box here, here is a simple process  
            message.setText(R.string.task_started);
 } 
   
 @Override    
 protected   void onProgressUpdate(Integer... values) {
 // Update progress  
              System.out.println( "" +values[ 0 ]);
              message.setText( "" +values[ 0 ]);
              pdialog.setProgress(values[ 0 ]);
 } 
   
 } 
   
 }

8.Solution to the problem that Spinner cannot be used in dialog and tabhost

9. Eclipse associated with JDK source code

(1). Click "window" -> "Preferences" -> "Java" -> "Installed JRES"

(2). At this time, there is a list pane to the right of "Installed JRES", which lists the JRE environments in the system. Select your JRE and click "Edit..." on the side. A window (Edit JRE) will appear.

(3). Select the rt.jar file: "c:\program files\java\jre_1.5.0_06\lib\rt.jar" and click the "+" sign on the left to expand it.

(4). After expanding, you can see "Source Attachment: (none)". Click this item, click the button on the right "Source Attachment...", and select the "src.zip" file in your JDK directory.

10.Unable to open sync connection!

Restart USB debugging in settings

11. EditText cursor position setting problem
When there is some preset text in EditText, I want to move the cursor to the front. I first used setSelection(0), but it turned out to have problems on Samsung P1000. After some research, I found that I need to call EditText.requestFocus() first, and then call setSelection(0). Otherwise, there will be problems on 2.x machines, but it works fine on 3.x.

12. The Home button in Android is reserved by the system, so you can't use onKeyDown like listening to the back button, but you can add your own processing code based on some events of the activity and view that will be triggered when the home button is pressed. Some people on the Internet say that you can use onAttachWindow to intercept the Home button, but I haven't tried it.

13. When rendering with surfaceView, if you want other Views to appear when needed, you can put surfaceView and other Views in layout, and hide other Views at ordinary times.

14. Use android:imeOptinos to set some interface settings for Android's built-in soft keyboard:

 android:imeOptions= "flagNoExtractUi"    // Make the soft keyboard not display in full screen, but only occupy part of the screen  
 At the same time, this property can also control the display content of the key in the lower right corner of the soft keyboard. By default, it is the Enter key.
 android:imeOptions= "actionNone"    //No prompt on the right side of the input box  
 android:imeOptions= "actionGo"      //The button in the lower right corner is 'Start'  
 android:imeOptions= "actionSearch"    //The button in the lower right corner is a magnifying glass image, search  
 android:imeOptions= "actionSend"      //The button in the lower right corner is 'Send'  
 android:imeOptions= "actionNext"     //The button in the lower right corner is 'Next'  
 android:imeOptions= "actionDone"    //The content of the button in the lower right corner is 'Done'  

15. Add shadow to TextView

 <style name= "Overlay" >
    <item name= "android:paddingLeft" >2dip</item>
    <item name= "android:paddingBottom" >2dip</item>
    <item name= "android:textColor" >#ffffff</item>
    <item name= "android:textSize" >12sp</item>
    <item name= "android:shadowColor" >#00ff00</item>
    <item name= "android:shadowDx" > 5 </item>
    <item name= "android:shadowDy" > 3 </item>
    <item name= "android:shadowRadius" > 6 </item>
 </style> 
     
 <TextView android:id= "@+id/test"       
       android:layout_width= "fill_parent"       
       android:layout_height= "wrap_content"       
       style= "@style/<span style=" background-color: rgb( 250 , 250 , 250 ); font-family: Helvetica, Tahoma, Arial, sans-serif; ">Overlay</span>"       
 android:text= "test"       
       android:gravity= "center" />

16. How to set the Chinese in TextView to bold?
Using android:textStyle="bold" in the XML file can set English to bold, but it cannot set Chinese to bold. The method to set Chinese to bold is:
TextView tv = (TextView)findViewById(R.id.TextView01);
TextPaint tp = tv.getPaint();
tp.setFakeBoldText(true);