安卓 SharedPreferences(功能：实现记住密码)
一.SharedPreferences
2.如何存储数据
步骤1：得到SharedPreferences对象 getSharedPreferences(“文件的名称”,“文件的类型”);
(1).Context.MODE_PRIVATE:指定该SharedPreferences数据只能被应用程序读写
(2).Context.MODE_WORLD_READABLE:指定该SharedPreferences数据能被其他应用程序读，但不能写。
(3).Context,MODE_WORLD_WRITEABLE:指定该SharedPreferences数据能被其他应用程序写，但不能读。
步骤2：得到 SharedPreferences.Editor编辑对象
SharedPreferences.Editor editor=sp.edit();
步骤3：添加数据
editor.putBoolean(key,value)
editor.putString()
editor.putInt()
editor.putFloat()
editor.putLong()
步骤4：提交数据 editor.commit()
//写数据 代码如下
// An highlighted block
public void write(){
SharedPreferences preferences = getSharedPreferences("yangzhibin",MODE_PRIVATE);
SharedPreferences.Editor edit = preferences.edit();
edit.putString("message","AAbcdea22dferwplkCC321ou1");
edit.commit();
}
3.如何读取数据
步骤1：得到SharedPreferences对象 getSharedPreferences(“文件的名称”,“文件的类型”);
步骤2：读取数据 String msg = sp.getString(key,defValue);
//读数据 代码如下
// An highlighted block
SharedPreferences preferences = getSharedPreferences("yangzhibin",MODE_PRIVATE);
String message = preferences.getString("message", "");
二.文件存储：内部文件存储+外部文件存储(SD卡)(******)
1.一般手机文件管理 根路径 /storage/emulated/0/或者/mnt/shell/emulated/0
2.重要代码：
(1)Environment.getExternalStorageState();// 判断SD卡是否
(2)Environment.getExternalStorageDirectory(); 获取SD卡的根目录
(3)Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES); 获取SD卡公开目录pictures文件夹
3.必须要添加读写SD卡的权限
// An highlighted block
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"></uses-permission>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>
读写json字符串
向sdk写入数据 代码如下：
// An highlighted block
private void write_json(String message) {
if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
File path = Environment.getExternalStorageDirectory();
File file1 = new File(path,"1702C//杨智斌");
if (!file1.exists()){
file1.mkdirs();
}
FileOutputStream fos = null;
try {
fos = new FileOutputStream(new File(file1,"readTwo.txt"));
fos.write(message.getBytes());
} catch (Exception e) {
e.printStackTrace();
}finally {
if (fos!=null){
try {
fos.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
从sdk读取数据 代码如下：
public static String read_json() {
if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
File file = Environment.getExternalStorageDirectory();
FileInputStream is= null;
StringBuffer sb=new StringBuffer();
try {
inputStream=new FileInputStream(new File(file,"readTwo.txt"));
byte[] b=new byte[1024];
int len=0;
while((len=is.read(b))!=-1){
sb.append(new String(b,0,len));
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally{
if(inputStream!=null){
try {
inputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return sb.toString();
}else{
return "";
}
}
## 三级缓存
1.内存工具类
```javascript
// An highlighted block
public class LruUtils {
private LruCache<String, Bitmap> lruCache;
private Long max = Runtime.getRuntime().maxMemory();//获得手机的最大内容
public LruUtils(){
lruCache = new LruCache<String, Bitmap>((int) (max/8)){
@Override
protected int sizeOf(String key, Bitmap value) {
return value.getByteCount();
}
};
}
public Bitmap getBitmap(String key){
return lruCache.get(key);
}
public void setBitamap(String key,Bitmap bitmap){
lruCache.put(key,bitmap);
}
}
2.sdk工具类
public class SDKutils {
//存图片
public Bitmap getBitmap(String name){
//获取图片路径
if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
File file = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES);
File file1 = new File(file,name);
return BitmapFactory.decodeFile(file1.getAbsolutePath());
}
return null;
}
//读图片
public void setBitmap(String name,Bitmap bitmap){
if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
File file = Environment.getExternalStoragePublicDirectory(Environment.MEDIA_BAD_REMOVAL);
File file1 = new File(file,name);
try {
bitmap.compress(Bitmap.CompressFormat.JPEG,100,new FileOutputStream(file1));
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}
}
}
3.网络请求工具类
public class HttpTools {
public static Bitmap getBitmap(String URL) throws ExecutionException, InterruptedException {
return new MyTask().execute(URL).get();
}
static class MyTask extends AsyncTask<String,String,Bitmap>{
@Override
protected Bitmap doInBackground(String... strings) {
String imageUrl = strings[0];
HttpURLConnection httpURLConnection = null;
try {
URL url = new URL(imageUrl);
httpURLConnection = (HttpURLConnection) url.openConnection();
httpURLConnection.setRequestMethod("GET");
httpURLConnection.connect();
if (httpURLConnection.getResponseCode() == 200){
InputStream is = httpURLConnection.getInputStream();
Bitmap bitmap = BitmapFactory.decodeStream(is);
return bitmap;
}
} catch (Exception e) {
e.printStackTrace();
}finally {
try {
if (httpURLConnection!=null){
httpURLConnection.disconnect();
}
} catch (Exception e) {
e.printStackTrace();
}
}
return null;
}
}
}
4.使用3个工具类，实现三级缓存
// An highlighted block
public class SendActivity extends AppCompatActivity {
Button button;
ImageView imageView;
LruUtils lruUtils = new LruUtils();
HttpToos httpToos = new HttpToos();
SDKutils sdKutils = new SDKutils();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_send);
button = findViewById(R.id.buttonone);
imageView = findViewById(R.id.imagetwo);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
try {
Cache_images();
} catch (ExecutionException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
}
public void Cache_images() throws ExecutionException, InterruptedException {
Bitmap bitmap = lruUtils.getBitmap("背景");
if (bitmap!=null){
imageView.setImageBitmap(bitmap);
Toast.makeText(this, "图片来自缓存中", Toast.LENGTH_SHORT).show();
}else{
bitmap = sdKutils.getBitmap("背景.jpg");
if (bitmap!=null){
imageView.setImageBitmap(bitmap);
new LruUtils().setBitamap("背景",bitmap);
Toast.makeText(this, "图片来自Sdk中", Toast.LENGTH_SHORT).show();
}else{
bitmap = httpToos.getBitmap("http://img02.tooopen.com/images/20150507/tooopen_sy_122395947985.jpg");
if (bitmap!=null){
imageView.setImageBitmap(bitmap);
lruUtils.setBitamap("背景",bitmap);
sdKutils.setBitmap("背景.jpg",bitmap);
Toast.makeText(this, "图片从网络上获取", Toast.LENGTH_SHORT).show();
}
}
}
}
}