Android Master / Detail流程-在Activity中操作Detail片段视图

Question

So I am new to Android development, and trying to wrap my head around the Master/Detail flow design. As such, I'm using the default classes Eclipse creates for you - so ScreenDetailActivity , ScreenDetailFragment , ScreenListActivity , and ScreenListFragment . One of my Detail fragments uses a layout that contains a series of checks and fields for entering data, and a button that is supposed to make the Activity class using the fragment pass that data to a calculator class, which then performs some basic calculations with the data. For example, found in the calculation_layout.xml file used by one of the Detail fragment in question:

<EditText android:id="@+id/edit_value"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:inputType="numberDecimal|numberSigned"
      android:hint="@string/background_value" />

<Button android:layout_width="wrap_content"
    android:layout_height="wrap_content" 
    android:text="@string/button_singleCalc"
    android:onClick="calculate" />

I think I have the the Button's calculate function working (ie the app doesn't crash when the calculate is empty or does trivial things); it's implemented in both ScreenListActivity and ScreenDetailActivity , since either could be using the fragment.

However, whenever I try to access the EditText objects in the Detail fragment, the app crashes. I'm trying something like this:

public void calculate(View view){
    //Retrieve all the information, and set the values in the Calculator
    EditText editText = (EditText) findViewById(R.id.edit_value);
    String number = editText.getText().toString();
    double angle = Double.parseDouble(number);

    Calculator.longCalc();
}

And inflating the layout in my ScreenDetailFragment like this, not unlike how the default method generated by Eclipse works (where mItem is basically an instance of a little class containing information on which fragment should be displazed):

public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {
        // The returned view
        View rootView;
        // If mItem is non-null...
        if (mItem != null) {
            if (mItem.title == "Calculation") {
                // If the title is Calculation, use the calculation layout
                rootView = inflater.inflate(R.layout.calculation_layout, container, false);
            } else {
                // Otherwise, show the dummy content as text in a TextView
                rootView = inflater.inflate(R.layout.fragment_screen_detail, container, false);
                ((TextView) rootView.findViewById(R.id.screen_detail)).setText(mItem.title);
            }
        } else {
            rootView = inflater.inflate(R.layout.fragment_screen_detail, container, false);
        }

        return rootView;
    }

The result, as said earlier, is a crash.

I assume that what I am supposed to do is somehow access rootView from the Activity, but I don't really know how to do that safely and effectively.

Can someone give me some pointers here?

UPDATE:

I have tried implementing OnClickListener, setting it up as such when that particular layout is inflated:

((Button)rootView.findViewById(R.id.button_calc)).setOnClickListener(this);

and implementing the onClick(View) function as such:

public void onClick(View view) {
        //Retrieve all the information, and set the values in the Calculator
        view = (View) view.getParent();
        EditText editText = (EditText) layout.findViewById(R.id.edit_phiD);
        String number = editText.getText().toString();

        Calculator.angle = Double.parseDouble(number) * 2.0 * Math.PI/360.0;

        Calculator.longCalc();
    }

However, the error persists. It also persists if I recast the ViewParent to a LinearLayout , a ViewGroup , or if I use view straight as is comes. To be clear, I am trying to get at the parent layout of the button that was clicked, so that I can go back down into that layout's other child Views and access their states.

Answer 1

You don't need to go through your activity in order to achieve this. Remove the onclick line and add an id for the button in your layout:

<Button android:id="@+id/calc_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content" 
android:text="@string/button_singleCalc" />

Then, simply add an OnClickListener to your button within your Fragment. Something like that:

private View mRootView;
private  EditText mEditText;

public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    // If mItem is non-null...
    if (mItem != null) {
        if (mItem.title == "Calculation") {
            // If the title is Calculation, use the calculation layout
            mRootView = inflater.inflate(R.layout.calculation_layout, container, false);
            mEditText = (EditText) mRootView.findViewById(R.id.edit_phiD);    
            ((Button)mRootView.findViewById(R.id.calc_button)).setOnClickListener(this);         
        } else {
            // Otherwise, show the dummy content as text in a TextView
            mRootView = inflater.inflate(R.layout.fragment_screen_detail, container, false);
            ((TextView) mRootView .findViewById(R.id.screen_detail)).setText(mItem.title);
        }
    } else {
        mRootView = inflater.inflate(R.layout.fragment_screen_detail, container, false);
    }

    return mRootView;
}

(Your fragment needs to implement OnClickListener for this). Then you'll get a callback on your Fragment, and here's what you do there:

public void onClick(View v){
    //Retrieve all the information, and set the values in the Calculator
    String number = mEditText.getText().toString();
    double angle = Double.parseDouble(number);

    Calculator.longCalc();
}

Answer 2

https://developer.android.com/training/basics/fragments/index.html

This is the best example, there are two fragments headlinesfragment and articlefragment with dynamic UI, follow how they have interface on articlefragment to let which headline is picked. Follow the tutorial properly. You should understand it well.