我遇到了问题。这是一个String语言，我有MainActivity（A）和ChooseLanguageActivity（B）。从用户到B选择语言之后，他打算用A语言，语言从意图中获得价值。我需要为这个变量语言设置默认值。我试着在onCreate中使用它。但是每次创建活动时我都不需要使用默认值。我需要在app启动之后才使用它，此变量需要使用它从活动B intent获得的值。 那是代码
public class MainActivity extends AppCompatActivity {
AppCompatButton chooseLanguageButton;
AppCompatButton cleanButton;
AppCompatEditText translatedTextOutput;
AppCompatEditText translatedTextInput;
String translatedInputString;
RequestQueue requestQueue;
SharedPreferences sPref;
final String SAVED_TEXT = "saved_text";
final String TAG = "myTag";
String language;
private ProgressBar progressBar;
private Timer timer;
private TextWatcher searchTextWatcher = new TextWatcher() {
@Override
public void afterTextChanged(Editable arg0) {
timer = new Timer();
timer.schedule(new TimerTask() {
@Override
public void run() {
if (translatedTextInput.getText().length() != 0){
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
MainActivity.this.runOnUiThread(new Runnable() {
@Override
public void run() {
requestQueue = Volley.newRequestQueue(MainActivity.this);
sendJsonRequest();
}
});
}
InputMethodManager in = (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE);
in.hideSoftInputFromWindow(translatedTextInput.getApplicationWindowToken(), InputMethodManager.HIDE_NOT_ALWAYS);
}
}, 600);
}
@Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {
}
@Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
if (timer != null) {
timer.cancel();
}
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
language = "en";
chooseLanguageButton = (AppCompatButton) findViewById(R.id.choose_language_button);
cleanButton = (AppCompatButton) findViewById(R.id.clean_button);
translatedTextOutput = (AppCompatEditText) findViewById(R.id.translated_text_field);
translatedTextInput = (AppCompatEditText) findViewById(R.id.translation_input_edit);
translatedTextInput.addTextChangedListener(searchTextWatcher);
chooseLanguageButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
saveText();
Intent intent = new Intent(MainActivity.this, ChooseLanguageList.class);
startActivity(intent);
}
});
cleanButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
translatedTextInput.setText("");
translatedTextOutput.setText("");
}
});
loadText();
}
@Override
protected void onDestroy() {
super.onDestroy();
sPref = null;
}
void saveText() {
sPref = getPreferences(MODE_PRIVATE);
SharedPreferences.Editor ed = sPref.edit();
ed.putString(SAVED_TEXT, translatedTextInput.getText().toString());
ed.commit();
Toast.makeText(this, "Text saved", Toast.LENGTH_SHORT).show();
}
void loadText() {
sPref = getPreferences(MODE_PRIVATE);
String savedText = sPref.getString(SAVED_TEXT, "");
translatedTextInput.setText(savedText);
Toast.makeText(this, "Text loaded", Toast.LENGTH_SHORT).show();
}
public void sendJsonRequest() {
Intent myIntent = getIntent();
language = myIntent.getStringExtra("short");
Log.v(getClass().getSimpleName(), "language short = " + language);
translatedInputString = translatedTextInput.getText().toString().replace(" ","+");
String url = String.format(getApplicationContext().getResources().getString(R.string.request_template),
String.format(getApplicationContext().getResources().getString(R.string.query_Template), translatedInputString, language ));
JsonObjectRequest jsObjRequest = new JsonObjectRequest
(Request.Method.GET, url, null, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
Log.v(TAG, "Inside OnResponse" + response.toString());
JSONArray results = null;
try {
results = response.getJSONObject("data").getJSONArray("translations");
for (int i=0,j=results.length();i<j;i++) {
String webTitle = results.getJSONObject(i).getString("translatedText");
translatedTextOutput.setText(webTitle);
}
} catch (JSONException e) {
Log.e(TAG, "Error :" + e);
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
if (error instanceof NetworkError) {
Log.e(TAG, "NetworkError");
} else if (error instanceof ServerError) {
Log.e(TAG, "The server could not be found. Please try again after some time!!");
} else if (error instanceof AuthFailureError) {
Log.e(TAG, "AuthFailureError");
} else if (error instanceof ParseError) {
Log.e(TAG, "Parsing error! Please try again after some time!!");
} else if (error instanceof NoConnectionError) {
Log.e(TAG, "NoConnectionError!");
} else if (error instanceof TimeoutError) {
Log.e(TAG, "Connection TimeOut! Please check your internet connection.");
}
}
});
requestQueue.add(jsObjRequest);
}
}
嗯。我不明白-1。如果你至少写了-1评论什么是错误的问题，不要在下次重复这个错误。
答案 0 :(得分：1)
当应用启动时，始终将变量设为false。在活动的onCreate里面说的是真的，那么你可以使用：
if (activityWasLauched == false){
//use the default
}
else{
//use a bundle and get the value from an intent
}
尽可能简化SharedPreferences的使用： 要在共享首选项中存储值：
SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(this);
SharedPreferences.Editor editor = sp.edit();
if(score > high_score)
{
editor.putInt("high_score", score);
editor.apply(); /* Edit the value here*/
}
从共享首选项中检索值：
SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(this);
String high_score= sp.getInt("high_score", "");
答案 1 :(得分：0)
请记住，变量存储在内存中，并在应用停止运行时销毁。要永久存储值，需要将其保存到磁盘。对于简单值，SharedPreferences是可行的方法。应用程序启动时，您应该从languages加载SharedPreferences的值。如果不存在此值，请保存默认值，以便下次启动应用程序时，它只读取值。如果应用中的某些内容更改了此变量的值（例如用户操作），请务必保存新值，以便下次应用启动时该值正确。
答案 2 :(得分：0)
希望我理解你......
<强>首先
启动你的＆＃34; ChooseLanguageList＆＃34;使用startActivityForResult（）
的活动Intent intent = new Intent(MainActivity.this, ChooseLanguageList.class);
startActivityForResult(intent, ANY_REQUEST_CODE);
<强>第二
在你的＆＃34; ChooseLanguageList＆＃34;将语言返回结果设置为＆＃34; MainActivity＆＃34;使用设置结果
Intent returnIntent = new Intent();
returnIntent.putExtra(MY_LANG_EXTRA, language);
setResult(Activity.RESULT_OK, returnIntent);
finish();
<强>第三
返回＆＃34; MainActivity＆＃34; ..使用onActivityResult捕获返回的结果
@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == ANY_REQUEST_CODE && resultCode == Activity.RESULT_OK) {
language = data.getStringExtra(MY_LANG_EXTRA);
/* Save language in Shared Preferences */
}
<强>第四：
将检索到的语言保存在共享首选项
中SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(this);
SharedPreferences.Editor editor = sp.edit();
editor.putInt(/*Key:*/"my_lang", /*value:*/language);
editor.apply();
<强>第五：
现在每次你想要使用语言时（例如在onCreate（）中），只需从共享首选项中检索它，并在找不到默认值时
String language = sp.getString(/*Key:*/"my_lang", "en/*Default value*/");
现在每次＆＃34; MainActivity＆＃34;启动它将尝试使用密钥＆＃34; my_lang＆＃34;从共享首选项获取语言，但如果没有任何内容，它将回退到默认＆＃34; en＆＃34;直到从＆＃34; ChooseLanguageList＆＃34;中检索到新值。活性。
希望这能回答你的问题