在android中控制后退“按钮”
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时间：2020-08-20 02:52:46 来源:igfitidea点击:
Control the back "button" in android
提问by Dennie
I want to get the Text data value from Sub-Activity back. And everything is ok. But when the Sub-activity was opened, then I just click back "button" on the phone, it throw an exception error. I found on the android NotePad life-cycle control toturial but It's hard to understand. Can someone help me? This is my code:
我想从子活动中取回文本数据值。一切正常。但是当打开子活动时，我只需单击手机上的返回“按钮”，它就会抛出异常错误。我在android NotePad 生命周期控制toturial 上找到了，但很难理解。有人能帮我吗？这是我的代码：
public class SBooks extends ListActivity {
private String title_raw;
private SBooksDbAdapter mDbHelper;
private static final int ACTIVITY_SEARCH = 0;
private static final int SEARCH_ID = Menu.FIRST;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.sbooks_list);
mDbHelper = new SBooksDbAdapter(this);
mDbHelper.open();
}
// Create Menu Option
@Override
public boolean onCreateOptionsMenu(Menu menu) {
boolean result = super.onCreateOptionsMenu(menu);
menu.add(0, SEARCH_ID, 0, R.string.menu_search);
return result;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch(item.getItemId()){
case SEARCH_ID:
Intent intent = new Intent(this, SBooksSearch.class);
startActivityForResult(intent, ACTIVITY_SEARCH);
return super.onOptionsItemSelected(item);
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent intent){
super.onActivityResult(requestCode, resultCode, intent);
switch(requestCode){
case ACTIVITY_SEARCH:
Bundle bundle = intent.getExtras();
title_raw = bundle.getString(SBooksDbAdapter.KEY_TITLE_RAW);
if(title_raw!=null){
Cursor cursor = mDbHelper.searchData(title_raw);
String[] from = new String[]{ SBooksDbAdapter.KEY_ROWID,
SBooksDbAdapter.KEY_TITLE, SBooksDbAdapter.KEY_LYRICS };
int[] to = new int[]{ R.id.id, R.id.title, R.id.lyrics };
SimpleCursorAdapter adapter =
new SimpleCursorAdapter(this, R.layout.sbooks_row, cursor, from, to );
setListAdapter(adapter);
}
}
}
}
}
This is my Sub-Activity:
这是我的子活动：
public class SBooksSearch extends Activity {
private EditText mTextSearch;
private Button searchButton;
private SBooksDbAdapter mDbHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.sbooks_search);
mTextSearch = (EditText)findViewById(R.id.text_search);
searchButton = (Button)findViewById(R.id.btn_search);
searchButton.setOnClickListener(new View.OnClickListener(){
public void onClick(View v){
Intent intent = new Intent();
intent.putExtra(SBooksDbAdapter.KEY_TITLE_RAW, mTextSearch.getText().toString());
setResult(RESULT_OK, intent);
finish();
}
});
}
@Override
protected void onSaveInstanceState(Bundle outState){
super.onSaveInstanceState(outState);
}
@Override
protected void onPause(){
super.onPause();
checkState();
}
@Override
protected void onResume(){
super.onResume();
}
private void checkState() {
} }
This is Logcat:
这是 Logcat：
08-12 18:44:39.211: WARN/InputManagerService(581): Starting input on non-focused client com.android.internal.view.IInputMethodClient$Stub$Proxy@43719140 (uid=10004 pid=623)
08-12 18:44:39.510: INFO/ActivityManager(581): Displayed activity com.original.sbooks/.SBooks: 4934 ms
08-12 18:44:40.821: WARN/KeyCharacterMap(730): No keyboard for id 0
08-12 18:44:40.821: WARN/KeyCharacterMap(730): Using default keymap: /system/usr/keychars/qwerty.kcm.bin
08-12 18:44:41.412: INFO/ARMAssembler(581): generated scanline__00000177:03515104_00001A01_00000000 [ 64 ipp] (89 ins) at [0x297608:0x29776c] in 952924 ns
08-12 18:44:41.520: INFO/ARMAssembler(581): generated scanline__00000177:03515104_00000A01_00000000 [ 46 ipp] (70 ins) at [0x297798:0x2978b0] in 517061 ns
08-12 18:44:42.171: INFO/ActivityManager(581): Starting activity: Intent { comp={com.original.sbooks/com.original.sbooks.SBooksSearch} }
08-12 18:44:52.196: WARN/ActivityManager(581): Launch timeout has expired, giving up wake lock!
08-12 18:44:52.279: WARN/ActivityManager(581): Activity idle timeout for HistoryRecord{436bfc80 {com.original.sbooks/com.original.sbooks.SBooksSearch}}
08-12 18:44:57.350: DEBUG/dalvikvm(620): GC freed 4103 objects / 231808 bytes in 75ms
08-12 18:45:05.130: DEBUG/dalvikvm(649): GC freed 2604 objects / 150112 bytes in 88ms
08-12 18:45:10.120: DEBUG/dalvikvm(623): GC freed 2750 objects / 149592 bytes in 71ms
08-12 18:45:11.920: INFO/ActivityManager(581): Displayed activity com.original.sbooks/.SBooksSearch: 29748 ms
08-12 18:45:17.263: WARN/ActivityManager(581): Activity pause timeout for HistoryRecord{436bfc80 {com.original.sbooks/com.original.sbooks.SBooksSearch}}
08-12 18:45:26.762: WARN/ActivityManager(581): Launch timeout has expired, giving up wake lock!
08-12 18:45:27.272: WARN/ActivityManager(581): Activity idle timeout for HistoryRecord{435a7760 {com.original.sbooks/com.original.sbooks.SBooks}}
08-12 18:46:04.905: DEBUG/AndroidRuntime(730): Shutting down VM
08-12 18:46:04.905: WARN/dalvikvm(730): threadid=3: thread exiting with uncaught exception (group=0x4000fe70)
08-12 18:46:04.905: ERROR/AndroidRuntime(730): Uncaught handler: thread main exiting due to uncaught exception
08-12 18:46:04.991: ERROR/AndroidRuntime(730): java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=0, result=0, data=null} to activity {com.original.sbooks/com.original.sbooks.SBooks}: java.lang.NullPointerException
08-12 18:46:04.991: ERROR/AndroidRuntime(730): at android.app.ActivityThread.deliverResults(ActivityThread.java:3005)
08-12 18:46:04.991: ERROR/AndroidRuntime(730): at android.app.ActivityThread.handleSendResult(ActivityThread.java:3047)
08-12 18:46:04.991: ERROR/AndroidRuntime(730): at android.app.ActivityThread.access00(ActivityThread.java:112)
08-12 18:46:04.991: ERROR/AndroidRuntime(730): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1721)
08-12 18:46:04.991: ERROR/AndroidRuntime(730): at android.os.Handler.dispatchMessage(Handler.java:99)
08-12 18:46:04.991: ERROR/AndroidRuntime(730): at android.os.Looper.loop(Looper.java:123)
08-12 18:46:04.991: ERROR/AndroidRuntime(730): at android.app.ActivityThread.main(ActivityThread.java:3948)
08-12 18:46:04.991: ERROR/AndroidRuntime(730): at java.lang.reflect.Method.invokeNative(Native Method)
08-12 18:46:04.991: ERROR/AndroidRuntime(730): at java.lang.reflect.Method.invoke(Method.java:521)
08-12 18:46:04.991: ERROR/AndroidRuntime(730): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:782)
08-12 18:46:04.991: ERROR/AndroidRuntime(730): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:540)
08-12 18:46:04.991: ERROR/AndroidRuntime(730): at dalvik.system.NativeStart.main(Native Method)
08-12 18:46:04.991: ERROR/AndroidRuntime(730): Caused by: java.lang.NullPointerException
08-12 18:46:04.991: ERROR/AndroidRuntime(730): at com.original.sbooks.SBooks.onActivityResult(SBooks.java:111)
08-12 18:46:04.991: ERROR/AndroidRuntime(730): at android.app.Activity.dispatchActivityResult(Activity.java:3595)
08-12 18:46:04.991: ERROR/AndroidRuntime(730): at android.app.ActivityThread.deliverResults(ActivityThread.java:3001)
回答by Shaun K.
I think Nate is correct about the NPE at intent.getExtras().
我认为 Nate 对 intent.getExtras() 中的 NPE 是正确的。
You should be checking the value of your result code before you do anything. You also might want to check to make sure intent.hasExtra(SBooksDbAdapter.KEY_TITLE_RAW) before you get that value. So, something like this:
在做任何事情之前，您应该检查结果代码的值。在获得该值之前，您可能还需要检查以确保 intent.hasExtra(SBooksDbAdapter.KEY_TITLE_RAW) 。所以，像这样：
switch(requestCode){
case ACTIVITY_SEARCH:
if (resultCode == RESULT_OK && intent.hasExtra(SBooksDbAdapter.KEY_TITLE_RAW)) {
title_raw = intent.getStringExtra(SBooksDbAdapter.KEY_TITLE_RAW);
... do all that other stuff ...
}
}
回答by Nate
Try putting in some logging into the onActivityResult(...) method of your main activity. The "back" button from the subactivity may be giving you a result code of RESULT_CANCELED, and the intent can be null in that case. So you'll get an NPE at
尝试在主要活动的 onActivityResult(...) 方法中输入一些日志。子活动中的“后退”按钮可能会为您提供 RESULT_CANCELED 的结果代码，在这种情况下，意图可以为空。所以你会得到一个 NPE
Bundle bundle = intent.getExtras();
捆绑包 = intent.getExtras();
