我正在尝试将我的应用程序切换为使用对话框 fragment ，但是在对话框可见时旋转屏幕时出现应用程序崩溃。我可以在下面描述的一个非常简单的应用程序中重现这一点。在 Android Studio 中创建一个新项目并添加一个 DialogFragment，如下所示:
public class MainActivity extends ActionBarActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
if (savedInstanceState == null) {
(new Handler()).postDelayed(new Runnable() {
@Override
public void run() {
AlertDialog dialog = new AlertDialog.Builder(MainActivity.this)
.setMessage("Alert")
.setTitle("My Alert")
.create();
MyDialogFragment dialogFragment = new MyDialogFragment();
dialogFragment.setDialog(dialog);
dialogFragment.show(getSupportFragmentManager(), "dialog");
}
}, 1000);
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
}
@Override
public void onActivityCreated(Bundle savedState) {
super.onActivityCreated(savedState);
}
}
public static class MyDialogFragment extends DialogFragment {
private Dialog mDialog;
public MyDialogFragment() {
super();
mDialog = null;
}
@Override
public void onCreate(Bundle state) {
super.onCreate(state);
}
// Set the dialog to display
public void setDialog(Dialog dialog) {
mDialog = dialog;
}
// Return a Dialog to the DialogFragment.
@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
return mDialog;
}
}
}
现在运行应用程序，在对话框出现后(加载后 1 秒)，旋转屏幕。请注意，我只在上面的初始 onCreate 上创建对话框。
这是我得到的异常(exception):
01-30 11:19:40.199 31986-31986/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.testdialogs, PID: 31986
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.testdialogs/com.example.testdialogs.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2215)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2265)
at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3758)
at android.app.ActivityThread.access$900(ActivityThread.java:145)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1212)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5081)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:781)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at android.support.v4.app.DialogFragment.onActivityCreated(DialogFragment.java:368)
at android.support.v4.app.Fragment.performActivityCreated(Fragment.java:1508)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:947)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1086)
at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:1884)
at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:566)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1171)
at android.app.Activity.performStart(Activity.java:5241)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2178)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2265)
at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3758)
at android.app.ActivityThread.access$900(ActivityThread.java:145)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1212)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5081)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:781)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
at dalvik.system.NativeStart.main(Native Method)
我的 gradle 脚本如下所示:
apply plugin: 'android'
android {
compileSdkVersion 19
buildToolsVersion "19.0.1"
defaultConfig {
minSdkVersion 9
targetSdkVersion 19
versionCode 1
versionName "1.0"
}
compileOptions {
sourceCompatibility JavaVersion.VERSION_1_7
targetCompatibility JavaVersion.VERSION_1_7
}
buildTypes {
release {
runProguard false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
}
}
}
dependencies {
compile 'com.android.support:appcompat-v7:+'
}
这只是您创建新项目并使用最新的 android 支持 jar 时的标准构建脚本。
我可以在 DialogFragment 的 onCreate 方法中执行 setRetainInstance ，然后它不会崩溃，但对话框在旋转时被关闭。这显然比崩溃要好，但不是我想要的。
我不确定使用 DialogFragments 的首选方式是什么，但我从直接来自 google 的一些示例代码(对于 google service sdk)中得到了这个想法。我想他们知道他们在做什么，所以我会使用相同的概念。
最佳答案
我通过子类化 DialogFragment 类并覆盖接下来的两个生命周期回调方法解决了这个问题:
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setRetainInstance(true);
}
@Override
public void onDestroyView() {
if (getDialog() != null && getRetainInstance()) {
getDialog().setDismissMessage(null);
}
super.onDestroyView();
}
关于Android 支持 DialogFragment 在屏幕旋转时崩溃，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/21465932/