Fragment save view state

问题

I have some Fragment with this structure:

    <RelativeLayout
        android:id="@+id/control_panel"
        android:visibility="gone">

        <RelativeLayout
            android:id="@+id/control_panel_icon">

            <ImageView
                android:id="@+id/control_panel_icon_1"
                android:src="@drawable/ic_control_panel_icon_1" />

            <ImageView
                android:id="@+id/control_panel_icon_2"
                android:src="@drawable/ic_control_panel_icon_2"
                android:visibility="gone"/>
        </RelativeLayout>

        <TextView
            android:id="@+id/control_panel_tv"
            android:text="@string/not_available" />
    </RelativeLayout>

And inside Fragment class i have onSaveInstanceState and onActivityCreated:

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putString("tv", panel_tv.getText().toString());
}

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    if (savedInstanceState != null) 
        panel_tv.setText(savedInstanceState.getString("tv"));
}

So it solves saving the state of TextView.

Inside Fragment class I also setup which image to display with some function:

public void setIcon(boolean condition){
    if (condition) {
         control_panel_icon_1.setVisibility(View.GONE);
         control_panel_icon_2.setVisibility(View.VISIBLE);
    } else {
         control_panel_icon_1.setVisibility(View.VISIBLE);
         control_panel_icon_2.setVisibility(View.GONE);
    }
}

Is there any way to save and restore which image is currently displayed?

I know, what I'm shouldn't save entire widgets, but if I can save state of RelativeLayout will it restore all it's child's states?

回答1:

Inside your Fragment class, declare a private variable:

private boolean condition; // rename to something more descriptive

Now in setIcon() store the value:

this.condition = condition;

Finally save this to the bundle in onSaveInstanceState():

outState.putBoolean("condition", this.condition);

and read it in onActivityCreated():

this.condition = savedInstanceState.getBoolean("condition");
this.setIcon(this.condition);

Note

You don't need to save the text from your TextView. The call to super.onSaveInstanceState() already takes care of this for you.

回答2:

You can either save the condition in outState like below:

outState.putBoolean("condition", condition);

and then read it and update the image views

setIcon(savedInstanceState.getBoolean("condition"))

Or You can save the visibility state of the image views by putInt method:

outState.putInt("ic1", control_panel_icon_1.getVisibility());
outState.putInt("ic2", control_panel_icon_2.getVisibility());

and then restore the state:

control_panel_icon_1.setVisibility(savedInstanceState.getInt("ic1"));
control_panel_icon_2.setVisibility(savedInstanceState.getInt("ic2"));

来源：https://stackoverflow.com/questions/51022120/fragment-save-view-state

标签

android

android-layout

android-fragments

onsaveinstancestate