android - 锁定和解锁屏幕后恢复 fragment

Question

我有 3(A,B,C) fragment 和一个 Activity 。在 Activity 中添加了 fragment A，然后替换了 fragment B、C。现在 fragment A 替换为 fragment B。在 fragment B 中，我添加了一些细节。然后我锁定解锁屏幕后的屏幕..它是带有 fragment A(已添加)的打开 Activity 。如何在锁定和解锁屏幕后恢复 fragment B

Answer 1

您应该将状态保存在扩展 Application 的类中类，导致 Activity 将在显示更改(发生锁屏或方向更改)后释放。

您的新应用程序类:

public class myApp extends Application {
   public int state; //field that keeps saved state

在你的 Activity 类中:

//add this method to save changed state
//then call it every time you change the fragment index
private void onChangeFragment(int stateid) {
    myApp sapp = (myApp) this.getApplication(); 
    sapp.state = stateid;
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);                            

    myApp sapp = (myApp) this.getApplication();              
    //restore fragment from sapp.state value
    switch (sapp.state) {
        case 0 : //fragment A
            {  setContentView(R.layout.fragmentA);
               //maybe Fragment newFragment = new MyFragmentA(); ... and so on
               break;  
            }
        case 1 : //fragment B
            {  setContentView(R.layout.fragmentB);
               //maybe Fragment newFragment = new MyFragmentB(); ... and so on
               break;  
            }
    }

里面的 list <application android:icon="@drawable/icon" android:label="@string/app_name" ...android:name=".myApp"`>

另一种方法是使用 Activity 先前通过 Bundle savedInstanceState 保存的状态.

在你的 Activity 类中:

private int state; //field that keeps saved state

@Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
    state = savedInstanceState.getInteger(FRAGMENT_STATE_KEY);
    //restore the fragment from state value here
    //switch (state) {....
    //....
}

// invoked when the activity may be temporarily destroyed, save the instance state here
@Override
public void onSaveInstanceState(Bundle outState) {
    out.putInteger(FRAGMENT_STATE_KEY, state);

    // call superclass to save any view hierarchy
    super.onSaveInstanceState(out);