Skip to main content

Saving a file in sdcard

Many a times, you want to save some contents permanently from your program. If the data is few words, you can save them in shared preferences. But for larger contents, you need to use a file.

To save a file in sdcard, first of all you should have the permission in your app. You should add this line in AndroidManifest.xml file. 

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>   
Next in code, you should open the file.


                File fl = new File("/mnt/sdcard/yourdirname","yourfilename");
                try {
   FileWriter wr = new FileWriter(fl);
   wr.write(str);//str is the string to be written to file
   wr.close();
  } catch (IOException e) {
    
   e.printStackTrace();
  }

For the File constructor, first parameter is directory name and second is filename. It is always better to write to another directory in sdcard. What happens if the directory does not exist? Your program will crash.

First ensure that the directory where you want to store file exists. If it does not, create it. Then create the file. To do that, you can use exists() function of File class.
could open the file.

               File dir = new File("/mnt/sdcard/yourdirname"); 
               if (!dir.exists() ){
                    if (!dir.mkdir()){ 
                       Toast.makeToast(context,"Unable to create directory",Toast.LENGTH_LONG).show(); 
                       return; 
                   } 
               } 
               File fl = new File(dir,"yourfilename");
              try {
                  FileWriter wr = new FileWriter(fl);
                  wr.write(str);//str is the string to be written to file
                  wr.close();
              } catch (IOException e) {

                  e.printStackTrace();
              }

If the directory does not exist, dir.exists() will be false. Then our code tries to create directory by using dir.mkdir().  If due to any reason, directory creation fails, mkdir() method returns false, and our code exits the function.

Once we have ensured that directory exists, we open the file and write to it.

If necessary the file can opened for appending, so that the contents are added to the end of existing file.


      FileWriter wr = new FileWriter(fl,true);//true to append, false to create new file
      wr.append(str);



Comments

Post a Comment

Popular posts from this blog

Simple ListView Adapter and list item select

When you are using a listview in your applications many a times you will write your own adapter to display item. But if your list is very simple showing a list of strings, you can use inbuilt adapters like ArrayAdapter, SimpleCursorAdapter etc.

ArrayAdapterLet us look at an example

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <ListView android:layout_height="wrap_content" android:id="@+id/listView1" android:layout_width="match_parent" android:layout_margin="20dp"> </ListView> </LinearLayout>

And add these lines to the onCreate method of the activity.

super.onCreate(savedInstanceState); …

Drawables in Android - Layer drawable

Let us see how to use layer drawable. You can have two or more bitmaps on different layers to create such a drawable

Using xml:

You should use layer-list in your xml file to create layerdrawable. Here is layer.xml
<?xml version="1.0" encoding="utf-8"?> <layer-list xmlns:android="http://schemas.android.com/apk/res/android"> <item> <bitmap android:src="@drawable/whiteicon" android:gravity="top|left"/> </item> <item> <bitmap android:src="@drawable/blueicon" android:gravity="top|left"/> </item> <item> <bitmap android:src="@drawable/redicon" android:gravity="top|left"/> </item> </layer-list>
We are using three different bitmaps whiteicon.png, redicon.png and blueicon.png which are present in /res/drawable/mdpi folder. All these are of different sizes and aligned to top left. This drawab…

DatePickers in Android

DatePicker is a view which lets the user select a date showing a calendar or 3 spinners for dd, mm and yy.

Let us see how to use this.
Easy Method: To use a DatePicker you can use DatePickerDialog. This can be created and shown programmatically too.

publicvoidonCreate(Bundle b){/*********/ Button btn =(Button)findViewById(R.id.btn); btn.setOnClickListener(new View.OnClickListener(){@OverridepublicvoidonClick(View v){ showPickerDialog();}});}privatevoidshowPickerDialog(){ DatePickerDialog dtPickerDlg =new DatePickerDialog(this,this, 2017,10,20); dtPickerDialog.show();}

In our xml file, let us have a button and in the onclick listener of the button, let us display the date picker dialog - we call showPickerDialog.

In showPickerDialog,  we are using a random date to initialize.

The first  parameter is the context. Second parameter is the class which implements the interface OnDateSetListener. Next three parameters are year, month (Jan is 0) and …