如何在 "onResume" 上更新 Activity？
How update an Activity on "onResume"?
我有一个包含一些文本的列表视图。但是当列表视图为空时，它将显示一个按钮，将您带到一个新的 activity，您可以在其中键入一些文本并保存在 SharedPreferences 上并完成。我希望 Listview 的 Activity 在另一个关闭时更新。我尝试了 onResume() 但由于某种原因它会永远保持刷新状态。我该怎么做？
顺便说一句，我正在更新使用：
startActivity(getIntent());
finish();
有更好的方法吗？
谢谢。
编辑--------------------------------------------
正如@Alex Loper 所说，我在 onResume() 方法中添加了 notifyDataSetOnChange() 。但是它崩溃了这个日志：
12-31 19:45:05.284 11864-11864/com.nerv.cas.partying E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.nerv.cas.partying, PID: 11864
java.lang.RuntimeException: Unable to resume activity {com.nerv.cas.partying/com.nerv.cas.partying.YourPartiesActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2812)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2845)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2262)
at android.app.ActivityThread.access0(ActivityThread.java:139)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5086)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.nerv.cas.partying.YourPartiesActivity.onResume(YourPartiesActivity.java:48)
at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1215)
at android.app.Activity.performResume(Activity.java:5327)
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2797)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2845)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2262)
at android.app.ActivityThread.access0(ActivityThread.java:139)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5086)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
我的class是这样的：
ArrayAdapter<String> adapter;
User user;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_your_parties);
user = getUserData();
fillUserParty(user);
fillAdapter(user);
ListView partiesListView = (ListView) findViewById(R.id.parties_list_view);
Button goToCreatePartyButton = (Button) findViewById(R.id.go_to_create_party_button);
if(adapter != null){
partiesListView.setVisibility(View.VISIBLE);
partiesListView.setAdapter(adapter);
}else{
goToCreatePartyButton.setVisibility(View.VISIBLE);
goToCreatePartyButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
startActivity(new Intent(YourPartiesActivity.this, CreatePartyActivity.class));
}
});
}
}
@Override
protected void onResume() {
super.onResume();
adapter.notifyDataSetChanged();
}
private void fillAdapter(User user){
List<Party> parties = user.getParties();
if(parties != null) {
for (int i = 0; i < parties.size(); i++) {
Party party = parties.get(i);
adapter.add(party.getName());
}
}
}
private void fillUserParty(User user){
SharedPreferences preferences = getSharedPreferences("Parties", MODE_PRIVATE);
int numOfParties = CreatePartyActivity.checkNumberOfParties(preferences);
for(int i=0; i<numOfParties; i++){
String partyName = preferences.getString("Name" + i, "");
if(partyName != ""){
int id = preferences.getInt("Id" + i, 0);
Party party = new Party(id, partyName);
user.joinParty(party);
}
}
}
public User getUserData(){
SharedPreferences preferences = getSharedPreferences("User", 0);
int id = preferences.getInt("Id", 0);
String username = preferences.getString("Username", "");
String name = preferences.getString("Name", "");
return new User(id, username, name);
}
在 onResume() 中调用列表视图适配器的 notifyDataSetChanged() 方法以使用新信息重绘列表视图。
编辑：根据发布的代码和堆栈跟踪，适配器在使用之前从未实例化，并导致 NPE。在调用 if(adapter != null){ 之前实例化适配器，以便正确填充它。
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_your_parties);
ListView partiesListView = (ListView) findViewById(R.id.parties_list_view);
adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1);
user = getUserData();
fillUserParty(user);
fillAdapter(user);
partiesListView.setAdapter(adapter);
Button goToCreatePartyButton = (Button) findViewById(R.id.go_to_create_party_button);
goToCreatePartyButton.setVisibility(View.VISIBLE);
goToCreatePartyButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
startActivity(new Intent(YourPartiesActivity.this, CreatePartyActivity.class));
}
});
}
如果您使用数据库和 "contentprovider"，您将能够使用 Loaders(LoaderCallback)，这将有助于监控底层数据源的变化。
你会发现，当第二个 activity 开始时，第一个 activity 调用 onpause，然后在大约 10 秒后有时调用 ondestroy。因此，依靠 onresume 来管理状态可能会很紧张
我在发布的代码中找不到初始化适配器。我认为适配器总是空的！
要解决空指针异常，像这样更改 onResume 方法：
@Override
protected void onResume() {
super.onResume();
if (adapter != null)
adapter.notifyDataSetChanged();
}
我有一个包含一些文本的列表视图。但是当列表视图为空时，它将显示一个按钮，将您带到一个新的 activity，您可以在其中键入一些文本并保存在 SharedPreferences 上并完成。我希望 Listview 的 Activity 在另一个关闭时更新。我尝试了 onResume() 但由于某种原因它会永远保持刷新状态。我该怎么做？
顺便说一句，我正在更新使用：startActivity(getIntent());
finish();
有更好的方法吗？
谢谢。
编辑--------------------------------------------
正如@Alex Loper 所说，我在 onResume() 方法中添加了 notifyDataSetOnChange() 。但是它崩溃了这个日志：
12-31 19:45:05.284 11864-11864/com.nerv.cas.partying E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.nerv.cas.partying, PID: 11864
java.lang.RuntimeException: Unable to resume activity {com.nerv.cas.partying/com.nerv.cas.partying.YourPartiesActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2812)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2845)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2262)
at android.app.ActivityThread.access0(ActivityThread.java:139)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5086)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.nerv.cas.partying.YourPartiesActivity.onResume(YourPartiesActivity.java:48)
at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1215)
at android.app.Activity.performResume(Activity.java:5327)
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2797)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2845)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2262)
at android.app.ActivityThread.access0(ActivityThread.java:139)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5086)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
at dalvik.system.NativeStart.main(Native Method)
我的class是这样的：
ArrayAdapter<String> adapter;
User user;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_your_parties);
user = getUserData();
fillUserParty(user);
fillAdapter(user);
ListView partiesListView = (ListView) findViewById(R.id.parties_list_view);
Button goToCreatePartyButton = (Button) findViewById(R.id.go_to_create_party_button);
if(adapter != null){
partiesListView.setVisibility(View.VISIBLE);
partiesListView.setAdapter(adapter);
}else{
goToCreatePartyButton.setVisibility(View.VISIBLE);
goToCreatePartyButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
startActivity(new Intent(YourPartiesActivity.this, CreatePartyActivity.class));
}
});
}
}
@Override
protected void onResume() {
super.onResume();
adapter.notifyDataSetChanged();
}
private void fillAdapter(User user){
List<Party> parties = user.getParties();
if(parties != null) {
for (int i = 0; i < parties.size(); i++) {
Party party = parties.get(i);
adapter.add(party.getName());
}
}
}
private void fillUserParty(User user){
SharedPreferences preferences = getSharedPreferences("Parties", MODE_PRIVATE);
int numOfParties = CreatePartyActivity.checkNumberOfParties(preferences);
for(int i=0; i<numOfParties; i++){
String partyName = preferences.getString("Name" + i, "");
if(partyName != ""){
int id = preferences.getInt("Id" + i, 0);
Party party = new Party(id, partyName);
user.joinParty(party);
}
}
}
public User getUserData(){
SharedPreferences preferences = getSharedPreferences("User", 0);
int id = preferences.getInt("Id", 0);
String username = preferences.getString("Username", "");
String name = preferences.getString("Name", "");
return new User(id, username, name);
}
在 onResume() 中调用列表视图适配器的 notifyDataSetChanged() 方法以使用新信息重绘列表视图。
编辑：根据发布的代码和堆栈跟踪，适配器在使用之前从未实例化，并导致 NPE。在调用 if(adapter != null){ 之前实例化适配器，以便正确填充它。
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_your_parties);
ListView partiesListView = (ListView) findViewById(R.id.parties_list_view);
adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1);
user = getUserData();
fillUserParty(user);
fillAdapter(user);
partiesListView.setAdapter(adapter);
Button goToCreatePartyButton = (Button) findViewById(R.id.go_to_create_party_button);
goToCreatePartyButton.setVisibility(View.VISIBLE);
goToCreatePartyButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
startActivity(new Intent(YourPartiesActivity.this, CreatePartyActivity.class));
}
});
}
如果您使用数据库和 "contentprovider"，您将能够使用 Loaders(LoaderCallback)，这将有助于监控底层数据源的变化。
你会发现，当第二个 activity 开始时，第一个 activity 调用 onpause，然后在大约 10 秒后有时调用 ondestroy。因此，依靠 onresume 来管理状态可能会很紧张
我在发布的代码中找不到初始化适配器。我认为适配器总是空的！
要解决空指针异常，像这样更改 onResume 方法：
@Override
protected void onResume() {
super.onResume();
if (adapter != null)
adapter.notifyDataSetChanged();
}