TextWatcher，實現(xiàn)該類需實現(xiàn)三個方法：

1.內(nèi)容變化前

public void beforeTextChanged(CharSequence s, int start,int count, int after);   

2.內(nèi)容變化中

public void onTextChanged(CharSequence s, int start, int before, int count);

3.內(nèi)容變化后

public void afterTextChanged(Editable s);

實現(xiàn)EditText的密碼可見與不可見

public class MainActivity extends AppCompatActivity {

    private EditText edit_pawd;
    private Button btnChange;
    private boolean flag = false;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        edit_pawd = (EditText) findViewById(R.id.edit_pawd);
        btnChange = (Button) findViewById(R.id.btnChange);
        edit_pawd.setHorizontallyScrolling(true);    //設(shè)置EditText不換行
        btnChange.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if(flag == true){
                    edit_pawd.setTransformationMethod(HideReturnsTransformationMethod.getInstance());
                    flag = false;
                    btnChange.setText("密碼不可見");
                }else{
                    edit_pawd.setTransformationMethod(PasswordTransformationMethod.getInstance());
                    flag = true;
                    btnChange.setText("密碼可見");
                }
            }
        });
    }
}