屏幕旋转
问题描述：
支持Android DialogFragment崩溃，我想转我的应用程序使用对话片段，但旋转屏幕时，而对话是可见的，我得到一个应用程序崩溃。我可以在下面描述的一个非常简单的应用程序中复制这个。创建Android Studio中一个新的项目并添加DialogFragment像这样：屏幕旋转
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;
}
}
}
现在运行的应用程序，并经过对话显示出来（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。
这里是例外即时得到：
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gradle这个脚本是这样的：
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:+'
}
当你创建一个新的项目，这就是标准的构建脚本，并使用了最新的Android支持jar。
我可以在DialogFragment的onCreate方法做setRetainInstance，然后它不会崩溃，但该对话框被驳回旋转。这显然比崩溃更好，但不是我正在寻找的东西。
我真的不知道用什么样的DialogFragments首选的方法是，但我从直接从谷歌一些示例代码（用于谷歌的服务SDK）这个想法。我想他们知道他们在做什么，所以我会用同样的概念。
答
当第一次创建活动中，savedInstanceState为null，因为它必须保存没有以前的状态。当屏幕旋转时，活动被破坏，并且onCreate(savedInstanceState)被再次调用并保存了一些状态（例如您的DialogFragment状态，这是可见的）。
所以，首先你savedInstaceState为空，当屏幕旋转时，实例的保存，然后在onCreate(savedInstanceState)恢复，所以它不是空了和任何内部if(savedInstanceState == null)将被调用，然后你得到了NullPointerException。
要解决此问题，删除此验证：
if(savedInstanceState == null){
///blablalba
}
答
我不想回答我的问题，但我想通了崩溃的原因。我需要实际上在DialogFragment的onCreateDialog中创建对话框，而不是从我的Activity中进行设置。不完全确定为什么这种情况。也许轮换时，android系统会删除与活动旧实例相关的引用。这并非完全理想，但我可以或许用来创建对话框中的数据传递
这里使用它的更新代码上旋转工作没有崩溃：
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() {
MyDialogFragment dialogFragment = new MyDialogFragment();
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 {
public MyDialogFragment() {
super();
}
@Override
public void onCreate(Bundle state) {
super.onCreate(state);
}
// Return a Dialog to the DialogFragment.
@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
return AlertDialog dialog = new AlertDialog.Builder(MainActivity.this)
.setMessage("Alert")
.setTitle("My Alert")
.create();
}
}
}
答
我解决了这样的通过子类DialogFragment类和压倒一切的接下来的两个生命周期回调方法的一个问题：这不是它在所有..我不希望显示一个新的对话框我想恢复以前的一个
@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();
}
没有。我想到了这一点，其实我还没有提交答案。我必须在DialogFragment的onCreateDialog中创建对话框。我传递给对话的实例似乎会导致问题。不确定究竟为什么。 –
@MattWolfe你应该使用MyDialogFragment类中的以前的对话状态，而不是Activity类，你试过了吗？ –