Android Tips (Dialog和线程中更新UI问题)

DialogFragment

• onCreate()中必须调用super.onCreate(savedInstanceState);

• 使用newInstance()方法来获取实例，使用setArguments来传递参数，避免在横竖屏切换的时候Fragment自动调用自己的无参构造函数，导致数据丢失。

  static MyDialogFragment newInstance(int num) {
          MyDialogFragment f = new MyDialogFragment();
  
          // Supply num input as an argument.
          Bundle args = new Bundle();
          args.putInt("num", num);
          f.setArguments(args);
  
          return f;
      }
  
      @Override
      public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          mNum = getArguments().getInt("num");
      }

• Dialog重复show()或者重复dismiss()会怎么样

mCustomDialog = CustomDialog.newInstance();
mCustomDialog.show(getFragmentManager(), "");
mCustomDialog.show(getFragmentManager(), "");

java.lang.IllegalStateException: Fragment already added: CustomDialog{70c4f46 #0 }

重复dismiss()没反应,看源码有做判断

void dismissInternal(boolean allowStateLoss) {
        if (mDismissed) {
            return;
        }
        mDismissed = true;
        mShownByMe = false;
        if (mDialog != null) {
            mDialog.dismiss();
            mDialog = null;
        }
        ....
    }

• 线程中创建和隐藏Dialog都没有问题,就是说Dialog的创建和隐藏不算是更新UI操作
• 不能再线程中创建Toast

java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()

Toast含有一个TN的成员，TN成员初始化时会new一个Handler,但是handler创建时会判断该线程是否Looper.prepare()过。

public Handler(Callback callback, boolean async) {
   //省略...

    mLooper = Looper.myLooper();
    if (mLooper == null) {
        throw new RuntimeException(
            "Can't create handler inside thread that has not called Looper.prepare()");
    }
    mQueue = mLooper.mQueue;
    mCallback = callback;
    mAsynchronous = async;
}

• 线程中启动Activity，关闭Activity不算更新UI.