Android入門之數據存儲那麼幾種方式

在實際的開發中，Android提供了5種數據存儲的方式：

1）文件存儲數據

2）使用SharedPreferences存儲數據

3）使用SQLite數據庫存儲數據

4）使用ContentProvide存儲數據

5）網絡存儲數據

 

一、文件存儲數據到內部存儲器

1）爲了保存文本到文件中，需要FileOutputStream類，openFileOutput方法用指定的模式打開一個指定的文件夾來寫入：

FileOutputStream fileOut = openFileOutput(“hello.txt”, Context.MODE_WORLD_WRITEABLE);

其中，有三種模式提供選擇：

Context.MODE_PRIVATE: 創建的文件只能被該應用程序讀寫

Context.MODE_WORLD_READABLE:允許其他應用程序讀取文件

Context.MODE_WORLD_WRITEABLE: 允許其他應用程序修改文件

2）爲了將字符流轉換爲字節流，需要OutputStreamWriter類的對象，並傳入FileOutputStream類的實例作爲參數：

OutputStreamWriter osw = newOutputStreamWriter(fileOut);

3）而讀取文件則需要用到FileInputStream類和InputStreamReader類：

FileInputStream fileInput = openFileInput(“hello.txt”);

InputStreamReader isr = new InputStreamReader(fileInput);

4）新建一個字符數組作爲緩衝器，把文件內容讀到緩衝器中，然後將其複製到String對象中

char[] inputBuffer = new char[READ_BLOCK_SIZE];

String s = “”;

int charRead;

while((charRead = isr.read(inputBuffer)>0){

       StringreadString = String.copyValueOf(inputBuffer, 0, charRead);

s +=readString;

inputBuffer= new char[READ_BLOCK_SIZE];

}

public class FilesActivity extends Activity {
	EditText textBox;
	static final int READ_BLOCK_SIZE = 100;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		this.textBox = (EditText)findViewById(R.id.txtText);
	}
	
	public void onClickSave(View v){
		String str = textBox.getText().toString();
		try {
			FileOutputStream fileOut = openFileOutput("hello.txt", MODE_WORLD_READABLE);
			OutputStreamWriter osw = new OutputStreamWriter(fileOut);			
			osw.write(str);
			osw.flush();
			osw.close();
			Toast.makeText(getBaseContext(), "File saved successfully!", 
					Toast.LENGTH_SHORT).show();
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
	}
	
	public void onClickLoad(View v){	
		try {
			FileInputStream fileInput = openFileInput("hello.txt");
			InputStreamReader isr = new InputStreamReader(fileInput);
			
			char[] inputBuffer = new char[READ_BLOCK_SIZE];
			String s = "";
			
			int charRead;
			while((charRead = isr.read(inputBuffer)) > 0){
				String readString = String.copyValueOf(inputBuffer, 0, charRead);
				s += readString;
				inputBuffer = new char[READ_BLOCK_SIZE];
			}
			textBox.setText(s);
			Toast.makeText(getBaseContext(), "File loaded successfully", 
					Toast.LENGTH_SHORT).show();			
			
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}		
	}

二、文件存儲數據到SD卡

返回sd卡的完整路徑：

File sdCard = Environment.getExternalStorageDirectory();

在SD卡中創建一個名問MyFiles的目錄，最終文件將會保存到這裏：

File directory = new File(sdCard.getAbsolutePath()+"/MyFiles");

directory.mkdir();

讀取SD卡需要在AndroidMinifest.xml文件中添加權限：

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE">      

</uses-permission>

其他的跟上面的一樣,下面看代碼：

 

public class FilesActivity extends Activity {
	EditText textBox;
	static final int READ_BLOCK_SIZE = 100;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		this.textBox = (EditText)findViewById(R.id.txtText);
	}
	
	public void onClickSave(View v){
		String str = textBox.getText().toString();
		try {
			File sdCard = Environment.getExternalStorageDirectory();//返回sd卡的路徑
			File directory = new File(sdCard.getAbsolutePath()+"/MyFiles");
			directory.mkdir();
			File file = new File(directory, "textfile.txt");
			FileOutputStream fileOut = new FileOutputStream(file);
			OutputStreamWriter osw = new OutputStreamWriter(fileOut);			
			osw.write(str);
			osw.flush();
			osw.close();
			Toast.makeText(getBaseContext(), "File saved successfully!", 
					Toast.LENGTH_SHORT).show();
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}	
	}
	
	public void onClickLoad(View v){		
		try {
			File sdCard = Environment.getExternalStorageDirectory();
			File directory = new File(sdCard.getAbsolutePath()+"/MyFiles");
			File file = new File(directory, "textfile.txt");
			FileInputStream fileIn;
			fileIn = new FileInputStream(file);
			InputStreamReader isr = new InputStreamReader(fileIn);
			char[] inputBuffer = new char[READ_BLOCK_SIZE];
			String s = "";
			
			int charRead;
			while((charRead = isr.read(inputBuffer)) > 0){
				String readString = String.copyValueOf(inputBuffer, 0, charRead);
				s += readString;
				inputBuffer = new char[READ_BLOCK_SIZE];
			}
			textBox.setText(s);
			Toast.makeText(getBaseContext(), "File loaded successfully", 
					Toast.LENGTH_SHORT).show();	
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}		
	}
}

二、使用SharedPreferences存儲數據

【存】                                                                                    

創建對象：

SharedPreferences sp = getSharedPreferences("FILE_NAME",MODE_PRIVATE);

創建編輯器：

SharedPreferences.Editor editor = sp.edit();

往編輯器存入int、boolean、String等類型的數據分別使用對應的方法：

editor.putBoolean("flag", true);

editor.putInt("age", 40);

editor.putString("你好啊，請多多指教","message");

編輯器必鬚髮送出去才能生效：

editor.commit();

【取】

還是需要SharedPreferences 對象：

SharedPreferences sp =getSharedPreferences("FILE_NAME",MODE_PRIVATE);

與set對應，取出對應的數據是get，如getBoolean、getString等：

booleanflag = sp.getBoolean("flag",false);

int age =sp.getInt("age", 0);

String mess = sp.getString("message","No message");

public class MainActivity extends Activity {
	private Button send,look;
	private EditText input;
	private TextView msg;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		this.msg = (TextView)findViewById(R.id.msg);		
		this.send = (Button)findViewById(R.id.send);
		this.look = (Button)findViewById(R.id.look);
		this.input = (EditText)findViewById(R.id.input);
		send.setOnClickListener(new View.OnClickListener() {			
			@Override
			public void onClick(View v) {
				SharedPreferences sp = getSharedPreferences("FILE_NAME", MODE_PRIVATE);	
				SharedPreferences.Editor editor = sp.edit();
				editor.putString("message",input.getText().toString());
				editor.commit();
				msg.setText("你有新的消息，請注意查收"); 
			}
		});
		look.setOnClickListener(new View.OnClickListener() {		
			@Override
			public void onClick(View v) {
				SharedPreferences sp = getSharedPreferences("FILE_NAME", MODE_PRIVATE);
				String mess = sp.getString("message", "No message");
				msg.setText(mess);
			}
		});
				
	}
}

三、使用靜態資源

也就是使用在res/raw文件夾下的文件。使用Activity類的getResources方法返回一個Resources對象，然後使用其openRawResource方法打開包含在res/raw文件夾下的文件。

public void onClickGetSources(View v){
		InputStream is = getBaseContext().getResources().openRawResource(R.raw.text);
		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();
		}
	}