Android的常用零碎代码块

1、在子线程中显示Toast提示

//子线程中显示Toast
public void ShowToast(String str) {
    Looper.prepare();
    Toast.makeText(getApplicationContext(), str, Toast.LENGTH_LONG).show();
    Looper.loop();
}

2、界面中按返回键，提示是否退出应用

//重写onKeyDown方法

private long exitTime = 0;
//主界面中按返回键，提示是否退出应用
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if (keyCode == KeyEvent.KEYCODE_BACK && event.getAction() == KeyEvent.ACTION_DOWN) {
        if ((System.currentTimeMillis() - exitTime) > 2000) {
            Toast.makeText(getApplicationContext(), "再按一次退出程序", Toast.LENGTH_SHORT).show();
            exitTime = System.currentTimeMillis();
        } else {
            finish();
            System.exit(0);
        }
        return true;
    }
    return super.onKeyDown(keyCode, event);
}

3、使用SharedPreferences和CheckBox保存用户名

①定义和初始化控件

private EditText loginEdit;
private CheckBox loginCheck;
private SharedPreferences sharedPreferences;
private SharedPreferences.Editor editors;
private String username;//获取到用户输入的用户名

loginEdit= (EditText) findViewById(R.id.activity_login_username);
loginCheck= (CheckBox) findViewById(R.id.activity_login_checkbox);
sharedPreferences= getSharedPreferences("LOGIN_SP", MODE_PRIVATE);
editors= sharedPreferences.edit();

②首先进入页面，判断LOGIN中是否有数据

String name= sp.getString("login", "");
if (name!= null) {
    loginCheck.setChecked(true);
    loginEdit.setText(name);
}

③当输入正确的用户名和密码登录之后

username= loginService.getText().toString().trim();
if (loginCheck.isChecked()) {
    editors.putString("login", username);
    editors.commit();
} else {
    editors.remove("login");
    editors.commit();
}