Android 动态修改Activity主题

public class MainActivity extends Activity {
    /** 系统自带主题 */
    private static final int DEFAULT_THEME = 0;
    /** 绿色 */
    private static final int GREEN_THEME = 1;
    /** 橘黄色 */
    private static final int ORANGE_THEME = 2;

    public static int current_theme = -1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        if (current_theme!= -1){
            this.setTheme(current_theme);
        }
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        findViewById(R.id.bt_theme).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                showChooseDialog();
            }
        });
    }


    public void changeTheme(int index) {
        switch (index) {
            case DEFAULT_THEME:
                current_theme = R.style.DefaultTheme;
                break;
            case GREEN_THEME:
                current_theme = R.style.GreenTheme;
                break;
            case ORANGE_THEME:
                current_theme = R.style.OrangeTheme;
                break;
            default:
                break;
        }
    }

    protected void reload() {
        Intent intent = getIntent();
        overridePendingTransition(0, 0);
        intent.addFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION);
        finish();
        overridePendingTransition(0, 0);
        startActivity(intent);
    }

    private int mCurrentWhich = 0;
    private int mTempWhich;
    private void showChooseDialog() {
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("选择主题");
        final String[] items = new String[] {"系统自带1","绿色","橘黄色" };
        //显示单选框,参1:单选字符串数组;参2:当前默认选中的位置;参3:选中监听
        builder.setSingleChoiceItems(items, mCurrentWhich,
                new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        mTempWhich = which;
                        Toast.makeText(MainActivity.this, items[which], Toast.LENGTH_SHORT).show();
                    }
                });

        builder.setPositiveButton("确定", new DialogInterface.OnClickListener() {

            @Override
            public void onClick(DialogInterface dialog, int which) {
                mCurrentWhich = mTempWhich;
                changeTheme(mCurrentWhich);
                reload();
            }
        });
        builder.setNegativeButton("取消", null);
        builder.show();
    }
}