我已经尝试了很多东西，但我的getActionBar（）。setDisplayHomeAsUpEnabled（true）;抛出空白
我还看到堆栈溢出的相对帖子，但它没有解决我的问题 我使用min SDK = 16并尝试从Mainactivity片段跳转到详细活动片段 我的意图很好，但在我的详细活动工具栏中，缺少后退按钮。 我的主要活动，我称之为jmp详细活动的意图 在setOnitemlistener方法中
package com.example.android.sunshine;
import android.content.Intent;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.text.format.Time;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
/**
* A placeholder fragment containing a simple view.
*/
public class MainActivityFragment extends Fragment {
String LOG_TAG = MainActivityFragment.class.getSimpleName();
ArrayAdapter<String> mForecastAdapter;
public MainActivityFragment() {
}
@Override
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setHasOptionsMenu(true);
}
@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater){
inflater.inflate(R.menu.menuitem,menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item){
int id = item.getItemId();
if(id == R.id.action_refresh){
FetchWeatherTask fetchWeatherTask = new FetchWeatherTask();
fetchWeatherTask.execute("Mathura","402c19fed0e53f9d92a81107ec2f6c2f");
}
return super.onOptionsItemSelected(item);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container,
false);
String[] forecastArray = {
"Sun May 1-CLEAR-31/17",
"Mon May 1-CLEAR-31/17",
"Tue May 1-CLEAR-31/17",
"Wed May 1-CLEAR-31/17",
"Thu May 1-CLEAR-31/17",
"Fri May 1-CLEAR-31/17",
"Sat May 1-CLEAR-31/17"
};
List<String> weekForecast = new ArrayList<String>
(Arrays.asList(forecastArray));
mForecastAdapter = new ArrayAdapter<String>
(getActivity()
,R.layout.listitemforecast,
R.id.listitemforecastText,
weekForecast
);
ListView listView =
(ListView)rootView.findViewById(R.id.list_textView);
listView.setAdapter(mForecastAdapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int
position, long id) {
String forecast = mForecastAdapter.getItem(position);
// Toast.makeText(getActivity(),forecast,
Toast.LENGTH_SHORT).show();
Intent intent = new Intent(getActivity(),DetailActivity.class)
.putExtra(Intent.EXTRA_TEXT,forecast);
try {
startActivity(intent);
}catch(Exception e)
{
Log.e(LOG_TAG,"error: "+ e);
}
}
});
return rootView;
}
public class FetchWeatherTask extends AsyncTask<String,Void,String[]> {
/* The date/time conversion code is going to be moved outside the
asynctask later,
* so for convenience we're breaking it out into its own method now.
*/
private String getReadableDateString(long time){
// Because the API returns a unix timestamp (measured in seconds),
// it must be converted to milliseconds in order to be converted to
valid date.
SimpleDateFormat shortenedDateFormat = new SimpleDateFormat("EEE
MMM dd");
return shortenedDateFormat.format(time);
}
/**
* Prepare the weather high/lows for presentation.
*/
private String formatHighLows(double high, double low) {
// For presentation, assume the user doesn't care about tenths of a
degree.
long roundedHigh = Math.round(high);
long roundedLow = Math.round(low);
String highLowStr = roundedHigh + "/" + roundedLow;
return highLowStr;
}
/**
* Take the String representing the complete forecast in JSON Format
and
* pull out the data we need to construct the Strings needed for the
wireframes.
*
* Fortunately parsing is easy: constructor takes the JSON string and
converts it
* into an Object hierarchy for us.
*/
private String[] getWeatherDataFromJson(String forecastJsonStr, int
numDays)
throws JSONException {
// These are the names of the JSON objects that need to be
extracted.
final String OWM_LIST = "list";
final String OWM_WEATHER = "weather";
// final String OWM_TEMPERATURE = "temp";
final String OWM_MAX = "temp_max";
final String OWM_MIN = "temp_min";
final String OWM_DESCRIPTION = "main";
JSONObject forecastJson = new JSONObject(forecastJsonStr);
JSONArray weatherArray = forecastJson.getJSONArray(OWM_LIST);
// OWM returns daily forecasts based upon the local time of the
city that is being
// asked for, which means that we need to know the GMT offset to
translate this data
// properly.
// Since this data is also sent in-order and the first day is
always the
// current day, we're going to take advantage of that to get a nice
// normalized UTC date for all of our weather.
Time dayTime = new Time();
dayTime.setToNow();
// we start at the day returned by local time. Otherwise this is a
mess.
int julianStartDay = Time.getJulianDay(System.currentTimeMillis(),
dayTime.gmtoff);
// now we work exclusively in UTC
dayTime = new Time();
String[] resultStrs = new String[numDays];
for(int i = 0; i < weatherArray.length(); i++) {
// For now, using the format "Day, description, hi/low"
String day;
String description;
String highAndLow;
// Get the JSON object representing the day
JSONObject dayForecast = weatherArray.getJSONObject(i);
// The date/time is returned as a long. We need to convert
that
// into something human-readable, since most people won't read
"1400356800" as
// "this saturday".
long dateTime;
// Cheating to convert this to UTC time, which is what we want
anyhow
dateTime = dayTime.setJulianDay(julianStartDay+i);
day = getReadableDateString(dateTime);
// description is in a child array called "weather", which is 1
element long.
JSONObject weatherObject =
dayForecast.getJSONArray(OWM_WEATHER).getJSONObject(0);
description = weatherObject.getString(OWM_DESCRIPTION);
// Temperatures are in a child object called "temp". Try not
to name variables
// "temp" when working with temperature. It confuses
everybody.
JSONObject temperatureObject =
dayForecast.getJSONObject(OWM_DESCRIPTION);
double high = temperatureObject.getDouble(OWM_MAX);
double low = temperatureObject.getDouble(OWM_MIN);
highAndLow = formatHighLows(high, low);
resultStrs[i] = day + " - " + description + " - " + highAndLow;
}
return resultStrs;
}
protected void onPostExecute(String[] Results){
mForecastAdapter.clear();
for(String day: Results){
mForecastAdapter.add(day);
}
}
protected String[] doInBackground(String... Params){
String LOG_TAG = FetchWeatherTask.class.getSimpleName();
// These two need to be declared outside the try/catch
// so that they can be closed in the finally block.
HttpURLConnection urlConnection = null;
BufferedReader reader = null;
// Will contain the raw JSON response as a string.
String forecastJsonStr = null;
String format = "json";
String units = "metric";
int NumDays = 7;
try {
String Place = "q";
String Mode = "mode";
String cnt = "cnt";
String Units = "units";
String Appid = "APPID";
// Construct the URL for the OpenWeatherMap query
// Possible parameters are avaiable at OWM's forecast API page,
at
// http://openweathermap.org/API#forecast
final String ForecastBaseURL =
"http://api.openweathermap.org/data/2.5/forecast?";
Uri builturi = Uri.parse(ForecastBaseURL).buildUpon()
.appendQueryParameter(Place,Params[0])
.appendQueryParameter(Mode,format)
.appendQueryParameter(cnt,Integer.toString(NumDays))
.appendQueryParameter(Units,units)
.appendQueryParameter(Appid,Params[1]).build();
URL url = new URL(builturi.toString());
// Log.v(LOG_TAG,"Built URI:"+builturi.toString());
// Create the request to OpenWeatherMap, and open the
connection
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("GET");
urlConnection.connect();
// Read the input stream into a String
InputStream inputStream = urlConnection.getInputStream();
StringBuffer buffer = new StringBuffer();
if (inputStream == null) {
// Nothing to do.
return null;
}
reader = new BufferedReader(new
InputStreamReader(inputStream));
String line;
while ((line = reader.readLine()) != null) {
// Since it's JSON, adding a newline isn't necessary (it
won't affect parsing)
// But it does make debugging a *lot* easier if you print
out the completed
// buffer for debugging.
buffer.append(line + "\n");
}
if (buffer.length() == 0) {
// Stream was empty. No point in parsing.
forecastJsonStr = null;
}
forecastJsonStr = buffer.toString();
} catch (IOException e) {
Log.e(LOG_TAG, "Error ", e);
// If the code didn't successfully get the weather data,
there's no point in attemping
// to parse it.
forecastJsonStr = null;
} finally{
if (urlConnection != null) {
urlConnection.disconnect();
}
if (reader != null) {
try {
reader.close();
} catch (final IOException e) {
Log.e(LOG_TAG, "Error closing stream", e);
}
}
}
try{
return getWeatherDataFromJson(forecastJsonStr,NumDays);
}catch (JSONException e){
Log.e(LOG_TAG,"json error" + e);
}
return null;
}
}
}
我的详细活动：
package com.example.android.sunshine;
import android.app.Activity;
import android.os.Bundle;
public class DetailActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_detail);
if(getActionBar() != null){
getActionBar().setDisplayHomeAsUpEnabled(true); // Here its
throwing null
}
}
}
我的详细信息fragment.java
package com.example.android.sunshine;
import android.app.Fragment;
import android.content.Intent;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
/**
* A placeholder fragment containing a simple view.
*/
public class DetailActivityFragment extends Fragment {
public DetailActivityFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootview = inflater.inflate(R.layout.fragment_detail, container,
false);
Intent intent = getActivity().getIntent();
if(intent != null && intent.hasExtra(Intent.EXTRA_TEXT))
{
String forecast = intent.getStringExtra(Intent.EXTRA_TEXT);
((TextView)rootview.findViewById(R.id.detail_text))
.setText(forecast);
}
return rootview;
}
}
我的主要活动：
package com.example.android.sunshine;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton)
findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action",
Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is
present.
getMenuInflater().inflate(R.menu.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();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
我的清单文件：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.android.sunshine">
<uses-permission android:name="android.permission.INTERNET" />
<application
android:allowBackup="true"
android:icon="@drawable/sunshine"
android:label="@string/app_name"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity
android:name=".MainActivity"
android:label="@string/app_name"
android:theme="@style/AppTheme.NoActionBar">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".DetailActivity"
android:label="@string/title_activity_detail"
android:theme="@style/AppTheme.NoActionBar"
android:parentActivityName=".MainActivity">
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="com.example.android.sunshine.MainActivity" />
</activity>
</application>
</manifest>
答案 0 :(得分：1)
与AndroidManifest.xml一样，您的活动使用没有操作栏的主题：
<activity
android:name=".DetailActivity"
android:label="@string/title_activity_detail"
android:theme="@style/AppTheme.NoActionBar"
android:parentActivityName=".MainActivity">
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="com.example.android.sunshine.MainActivity" />
</activity>
因此，您可以更改主题以解决问题。
答案 1 :(得分：0)
您的DetailActivity应该扩展AppCompatActivity
package com.example.android.sunshine;
import android.app.Activity;
import android.os.Bundle;
public class DetailActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_detail);
if(getActionBar() != null){
getActionBar().setDisplayHomeAsUpEnabled(true);
}
}
}
答案 2 :(得分：0)
删除DetailActivtity中的这部分代码
if(getActionBar() != null){
getActionBar().setDisplayHomeAsUpEnabled(true);
}
在onCreate方法之后实现此方法，您的后退按钮将会启动并开始工作。
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
NavUtils.navigateUpFromSameTask(this);
finish();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
答案 3 :(得分：0)
您需要扩展 AppCompatActivity ，详细信息活动
package com.example.android.sunshine;
import android.app.Activity;
import android.os.Bundle;
public class DetailActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_detail);
if(getSupportActionBar() != null){
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}
}
}
并检查您的样式文件
<style name="Theme.AppCompat.NoActionBar.FullScreen" parent="AppTheme">
<item name="android:windowNoTitle">true</item>
<item name="windowActionBar">false</item>
<item name="android:windowFullscreen">true</item>