今天要來介紹一下SharedPreferences，這是一個可以以Key-Value的方式來儲存資料，可以把它當作是一個簡單的小資料庫

首先先創立一個SharedPreferences

public class SharedPf {
    private String test;
    private SharedPreferences sharedPf;
    private Context context;
    public SharedPf(Context context){
        this.context = context;
        sharedPf=this.context.getSharedPreferences("USER",Context.MODE_PRIVATE);//設定MODE
    }

    public String getTest() {
        //拿取資料
        return sharedPf.getString("TEST","");
    }

    public void setTest(String test) {
       //設定資料
       sharedPf.edit().putString("TEST",test).commit();
    }
}

主要程式碼

public class MainActivity extends AppCompatActivity {
    private SharedPf sharedPf;
    private Button button;
    private Button button3;
    private EditText editText;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button = findViewById(R.id.button);
        button3 = findViewById(R.id.button3);
        editText = findViewById(R.id.editTextText);
        sharedPf = new SharedPf(this);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                sharedPf.setTest(editText.getText().toString());
                Toast.makeText(MainActivity.this,"已儲存資料" + editText.getText().toString() + "!",Toast.LENGTH_SHORT).show();
                editText.setText("");
            }
        });
        button3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                editText.setText(sharedPf.getTest());
                Toast.makeText(MainActivity.this,"已拿取資料!",Toast.LENGTH_SHORT).show();
            }
        });
    }
}

結果如下