Android開發入門（十八）文件 18.2保存到外部存儲設備（SD卡）

上一節介紹了如何把文件存儲到內部設備。有的時候，需要把文件存儲到外部存儲設備，比如SD卡。因為 SD卡具有更大的存儲空間，同時也可以很容易的和其他用戶分享這些文件。

使用上一節的例子，把用 戶輸入的文字保存在SD卡，修改onClick()事件。如下：

public class FilesActivity extends 

Activity {  
    EditText textBox;  
    static final int READ_BLOCK_SIZE = 100;  
      
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.main);  
      
        textBox = (EditText) findViewById(R.id.txtText1);  
              
        InputStream is = this.getResources().openRawResource(R.raw.textfile);  
        BufferedReader br = new BufferedReader(new InputStreamReader(is));  
        String str = null;  
        try {  
            while ((str = br.readLine()) != null) {  
                Toast.makeText(getBaseContext(),   
                    str, Toast.LENGTH_SHORT).show();  
            }  
            is.close();  
            br.close();  
        } catch (IOException e) {  
            e.printStackTrace();  
        }  
      
    }  
      
    public void onClickSave(View view) {  
        String str = textBox.getText().toString();  
        try
        {  
            //---SD Card Storage---  
            File sdCard = Environment.getExternalStorageDirectory();  
            File directory = new File (sdCard.getAbsolutePath() +  
                "/MyFiles");  
            directory.mkdirs();  
            File file = new File(directory, "textfile.txt");  
            FileOutputStream fOut = new FileOutputStream(file);  
      
            /*           
            FileOutputStream fOut = 
                    openFileOutput("textfile.txt", 
                            MODE_WORLD_READABLE); 
            */
                              
            OutputStreamWriter osw = new
                    OutputStreamWriter(fOut);  
      
            //---write the string to the file---  
            osw.write(str);  
            osw.flush();   
            osw.close();  
      
            //---display file saved message---  
            Toast.makeText(getBaseContext(),  
                    "File saved successfully!",  
                    Toast.LENGTH_SHORT).show();  
      
            //---clears the EditText---  
            textBox.setText("");  
        }  
        catch (IOException ioe)  
        {  
            ioe.printStackTrace();  
        }  
    }  
      
}

上面的代碼中，使用getExternalStorageDirectory()方法去獲取SD卡的路徑。通常，在真機上面 返回“/sdcard”，在模擬器上面返回"/mnt/sdcard"。但是，不要嘗試去寫死SD卡的路徑，因為 手機廠商有可能去給SD卡指定一個路徑。因此，確保使用getExternalStorageDirectory()方法去獲取SD卡的 路徑。

然後，創建一個MyFiles的文件夾。最終，把文件保存在這個文件夾中。

從外部設備 中加載文件，修改onClickLoad()方法：

public void onClickLoad(View view) {  
        try
        {  
            //---SD Storage---  
            File sdCard = Environment.getExternalStorageDirectory();  
            File directory = new File (sdCard.getAbsolutePath() +   
                "/MyFiles");  
            File file = new File(directory, "textfile.txt");  
            FileInputStream fIn = new FileInputStream(file);  
            InputStreamReader isr = new InputStreamReader(fIn);  
      
            /* 
            FileInputStream fIn =  
                    openFileInput("textfile.txt"); 
            InputStreamReader isr = new  
                    InputStreamReader(fIn); 
            */
                  
            char[] inputBuffer = new char[READ_BLOCK_SIZE];  
            String s = "";  
      
            int charRead;  
            while ((charRead = isr.read(inputBuffer))>0)  
            {  
                //---convert the chars to a String---  
                String readString =  
                        String.copyValueOf(inputBuffer, 0,  
                                charRead);  
                s += readString;  
      
                inputBuffer = new char[READ_BLOCK_SIZE];  
            }  
            //---set the EditText to the text that has been   
            // read---  
            textBox.setText(s);  
      
            Toast.makeText(getBaseContext(),  
                    "File loaded successfully!",  
                    Toast.LENGTH_SHORT).show();  
        }  
        catch (IOException ioe) {  
            ioe.printStackTrace();  
        }  
      
    }