我的android应用程序在启动时崩溃，在我尝试添加微调器之前，它运行良好，所以我确信这是问题所在，但我无法解决这是我的代码：
主要活动.java
package synctc.me.stormy;
import android.content.Context;
import android.graphics.drawable.Drawable;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.ProgressBar;
import android.widget.RelativeLayout;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;
import com.squareup.okhttp.Call;
import com.squareup.okhttp.Callback;
import com.squareup.okhttp.OkHttpClient;
import com.squareup.okhttp.Request;
import com.squareup.okhttp.Response;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.IOException;
import butterknife.ButterKnife;
import butterknife.InjectView;
public class MainActivity extends ActionBarActivity implements AdapterView.OnItemSelectedListener{
public static final String TAG = MainActivity.class.getSimpleName();
private CurrentWeather mCurrentWeather ;
@InjectView(R.id.timeLabel) TextView mTimeLabel;
@InjectView(R.id.temperatureLabel) TextView mTemperatureLabel;
@InjectView(R.id.humidityValue) TextView mHumidityValue;
@InjectView(R.id.precipValue) TextView mPrecipValue;
@InjectView(R.id.iconImageView) ImageView mIconImageView;
@InjectView(R.id.refreshImageView) ImageView mRefreshImageView;
@InjectView(R.id.progressBar)ProgressBar mProgressBar;
@InjectView(R.id.textView) TextView mTextView;
@InjectView(R.id.locationLabel) TextView mTimeZone;
Spinner spinner = (Spinner) findViewById(R.id.spinner);
double latitude = 31.956578300000000000;
double longitude = 35.945695099999966000;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this,
R.array.Country_array, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(adapter);
setContentView(R.layout.activity_main);
ButterKnife.inject(this);
mProgressBar.setVisibility(View.INVISIBLE);
mRefreshImageView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
getForecast(latitude,longitude);
}
});
getForecast(latitude,longitude);
Log.d(TAG, "Main ui is running");
}
private void getForecast(double latitude, double longitude) {
String apiKey="37ee485ed1ec27026ef5ff8948b6f94b";
String forecastUrl="https://api.forecast.io/forecast/"+apiKey+"/"+latitude+","+longitude;
if(isNetworkAvailable()){
OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder()
.url(forecastUrl)
.build();
Call call=client.newCall(request);
call.enqueue(new Callback() {
@Override
public void onFailure(Request request, IOException e) {
runOnUiThread(new Runnable() {
@Override
public void run() {
toggleRefresh();
}
});
alertUserAboutError();
}
@Override
public void onResponse(Response response) throws IOException {
runOnUiThread(new Runnable() {
@Override
public void run() {
toggleRefresh();
}
});
try {
String jsonData = response.body().string();
Log.v(TAG, jsonData);
if(response.isSuccessful()){
mCurrentWeather = getCurrentDetails(jsonData);
runOnUiThread(new Runnable() {
@Override
public void run() {
updateDisplay();
}
});
}else{
alertUserAboutError();
}
} catch (IOException e) {
Log.e(TAG, "Exception Caught : ",e);
}
catch (JSONException e){
Log.e(TAG, "Exception Caught : ",e);
}
}
});}
else{
Toast.makeText(this
, getString(R.string.network_unavailable_messege)
, Toast.LENGTH_LONG).show();
}
}
private void updateDisplay() {
mTemperatureLabel.setText(mCurrentWeather.getTemperature()+"");
mTimeLabel.setText("At" +mCurrentWeather.getFormattedTime()+"n"+" it will be ");
mHumidityValue.setText(mCurrentWeather.getHumidity()+"");
mPrecipValue.setText(mCurrentWeather.getPrecipChane()+"%");
mTextView.setText(mCurrentWeather.getSummary()+"");
Drawable drawable = getResources().getDrawable(mCurrentWeather.getIconId());
mIconImageView.setImageDrawable(drawable);
mTimeZone.setText(mCurrentWeather.getTimeZone()+"");
}
private CurrentWeather getCurrentDetails(String jsonData) throws JSONException{
JSONObject forecast = new JSONObject (jsonData);
String timezone = forecast.getString("timezone");
Log.i(TAG,"From JSON To:"+timezone);
JSONObject currently = new JSONObject(forecast.get("currently").toString());
CurrentWeather currentWeather = new CurrentWeather();
currentWeather.setHumidity(currently.getDouble("humidity"));
currentWeather.setTime(currently.getLong("time"));
currentWeather.setIcon(currently.getString("icon"));
currentWeather.setPrecipChane(currently.getDouble("precipProbability"));
currentWeather.setSummary(currently.getString("summary"));
currentWeather.setTemperature(currently.getDouble("temperature"));
double fehTemp = currentWeather.getTemperature();
double celTemp = ((fehTemp-32)*5)/9;
currentWeather.setTemperature(celTemp);
currentWeather.setTimeZone(timezone);
Log.d(TAG, currentWeather.getFormattedTime());
return currentWeather;
}
private boolean isNetworkAvailable() {
toggleRefresh();
ConnectivityManager manager = (ConnectivityManager)
getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo networkInfo = manager.getActiveNetworkInfo();
boolean isAvailable = false;
if(networkInfo != null &&networkInfo.isConnected()){
isAvailable=true ;
}
return isAvailable;
}
private void toggleRefresh() {
if(mProgressBar.getVisibility()== View.INVISIBLE) {
mProgressBar.setVisibility(View.VISIBLE);
mRefreshImageView.setVisibility(View.INVISIBLE);
}else{
mProgressBar.setVisibility(View.INVISIBLE);
mRefreshImageView.setVisibility(View.VISIBLE);
}
}
private void alertUserAboutError() {
AlertDialogFragment dialog = new AlertDialogFragment();
dialog.show(getFragmentManager(), "error_dialog");
}
@Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
String text = spinner.getSelectedItem().toString();
switch(text){
case "Jordan":
latitude = 31.956578300000000000;
longitude = 35.945695099999966000;
break;
case "Palestine":
latitude = 31.952162000000000000;
longitude = 35.233154000000010000;
break;
case "KSA":
latitude = 23.885942000000000000;
longitude = 45.079162000000000000;
break;
case "UAE":
latitude = 25.241151000000000000;
longitude = 55.365769000000000000;
break;
}
}
@Override
public void onNothingSelected(AdapterView<?> parent) {
}
}
AlertDialogFragment.java
package synctc.me.stormy;
import android.app.AlertDialog;
import android.app.Dialog;
import android.app.DialogFragment;
import android.content.Context;
import android.os.Bundle;
public class AlertDialogFragment extends DialogFragment {
@Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
Context context = getActivity();
AlertDialog.Builder builder = new AlertDialog.Builder(context)
.setTitle(context.getString(R.string.error_title))
.setMessage(context.getString(R.string.error_messege))
.setPositiveButton(context.getString(R.string.error_ok_button_text), null);
AlertDialog dialog = builder.create();
return dialog;
}
}
CurrentWeather.java
package synctc.me.stormy;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;
public class CurrentWeather {
private String mIcon;
private long mTime;
private double mTemperature;
private double mHumidity;
private double mPrecipChane;
private String mSummary;
private String mTimeZone;
public String getIcon() {
return mIcon;
}
public void setIcon(String icon) {
mIcon = icon;
}
public int getIconId(){
int iconId = R.mipmap.clear_day;
if (mIcon.equals("clear-day")) {
iconId = R.mipmap.clear_day;
}
else if (mIcon.equals("clear-night")) {
iconId = R.mipmap.clear_night;
}
else if (mIcon.equals("rain")) {
iconId = R.mipmap.rain;
}
else if (mIcon.equals("snow")) {
iconId = R.mipmap.snow;
}
else if (mIcon.equals("sleet")) {
iconId = R.mipmap.sleet;
}
else if (mIcon.equals("wind")) {
iconId = R.mipmap.wind;
}
else if (mIcon.equals("fog")) {
iconId = R.mipmap.fog;
}
else if (mIcon.equals("cloudy")) {
iconId = R.mipmap.cloudy;
}
else if (mIcon.equals("partly-cloudy-day")) {
iconId = R.mipmap.partly_cloudy;
}
else if (mIcon.equals("partly-cloudy-night")) {
iconId = R.mipmap.cloudy_night;
}
return iconId;
}
public long getTime() {
return mTime;
}
public String getFormattedTime(){
SimpleDateFormat formatter = new SimpleDateFormat("h:mm a");
formatter.setTimeZone(TimeZone.getTimeZone(getTimeZone()));
Date datetime = new Date(getTime()*1000);
String timeString = formatter.format(datetime);
return timeString;
}
public void setTime(long time) {
mTime = time;
}
public int getTemperature() {
return(int) Math.round(mTemperature);
}
public void setTemperature(double temperature) {
mTemperature = temperature;
}
public double getHumidity() {
return mHumidity;
}
public void setHumidity(double humidity) {
mHumidity = humidity;
}
public String getSummary() {
return mSummary;
}
public void setSummary(String summary) {
mSummary = summary;
}
public int getPrecipChane() {
double precipPercentage = mPrecipChane * 100;
return (int)Math.round(precipPercentage) ;
}
public String getTimeZone() {
return mTimeZone;
}
public void setTimeZone(String timeZone) {
mTimeZone = timeZone;
}
public void setPrecipChane(double precipChane) {
mPrecipChane = precipChane;
}
}
在strings.xml中，我放置了
<string-array name="Country_array">
<item>Jordan</item>
<item>Palestine</item>
<item>UAE</item>
<item>KSA</item>
</string-array>
这是整个logcat：
03-30 11:40:59.238 1901-1901/synctc.me.stormy D/AndroidRuntime﹕ Shutting down VM
--------- beginning of crash
03-30 11:40:59.239 1901-1901/synctc.me.stormy E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: synctc.me.stormy, PID: 1901
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{synctc.me.stormy/synctc.me.stormy.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.Activity.findViewById(Activity.java:2071)
at synctc.me.stormy.MainActivity.<init>(MainActivity.java:50)
at java.lang.reflect.Constructor.newInstance(Native Method)
at java.lang.Class.newInstance(Class.java:1572)
at android.app.Instrumentation.newActivity(Instrumentation.java:1065)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2199)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
03-30 11:41:08.206 2004-2004/synctc.me.stormy D/AndroidRuntime﹕ Shutting down VM
03-30 11:41:08.206 2004-2004/synctc.me.stormy E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: synctc.me.stormy, PID: 2004
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{synctc.me.stormy/synctc.me.stormy.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference
at android.app.Activity.findViewById(Activity.java:2071)
at synctc.me.stormy.MainActivity.<init>(MainActivity.java:50)
at java.lang.reflect.Constructor.newInstance(Native Method)
at java.lang.Class.newInstance(Class.java:1572)
at android.app.Instrumentation.newActivity(Instrumentation.java:1065)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2199)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Activity_min.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity"
android:background="#FFFC970B"
android:id="@+id/summaryLabel">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="100"
android:id="@+id/temperatureLabel"
android:layout_centerVertical="true"
android:layout_centerHorizontal="true"
android:textColor="@android:color/white"
android:textSize="150sp"
android:src="@mipmap/refresh"/>
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/degreeImageView"
android:layout_alignTop="@+id/temperatureLabel"
android:layout_toRightOf="@+id/temperatureLabel"
android:layout_toEndOf="@+id/temperatureLabel"
android:src="@mipmap/degree"
android:layout_marginTop="50dp"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="at 5:00pm it will be :"
android:id="@+id/timeLabel"
android:layout_above="@+id/temperatureLabel"
android:layout_centerHorizontal="true"
android:textColor="#80ffffff"
android:textSize="18sp"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Alcatraz Island, CA"
android:id="@+id/locationLabel"
android:layout_above="@+id/timeLabel"
android:layout_centerHorizontal="true"
android:layout_marginBottom="60dp"
android:textColor="@android:color/white"
android:textSize="24sp"/>
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/iconImageView"
android:layout_alignBottom="@+id/locationLabel"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:src="@mipmap/cloudy_night"/>
<LinearLayout
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="@+id/temperatureLabel"
android:layout_centerHorizontal="true"
android:layout_marginTop="10dp"
android:weightSum="100"
android:id="@+id/linearLayout">
<LinearLayout
android:orientation="vertical"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_weight="50"
android:touchscreenBlocksFocus="false">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="HUMIDITY"
android:id="@+id/humidityLabel"
android:textColor="#80ffffff"
android:gravity="center_horizontal"/>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="0.88"
android:id="@+id/humidityValue"
android:textColor="@android:color/white"
android:textSize="24sp"
android:gravity="center_horizontal"/>
</LinearLayout>
<LinearLayout
android:orientation="vertical"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_weight="50">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="RAIN/SNOW?"
android:id="@+id/precipLabel"
android:textColor="#80ffffff"
android:gravity="center_horizontal"/>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="100%"
android:id="@+id/precipValue"
android:textColor="@android:color/white"
android:textSize="24sp"
android:gravity="center_horizontal"/>
</LinearLayout>
</LinearLayout>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Stormy with a chance of meatballs"
android:id="@+id/textView"
android:layout_below="@+id/linearLayout"
android:layout_centerHorizontal="true"
android:layout_marginTop="40dp"
android:textColor="@android:color/white"
android:textSize="18dp"
android:gravity="center_vertical"/>
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/refreshImageView"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:src="@mipmap/refresh"/>
<ProgressBar
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/progressBar"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:layout_alignBottom="@+id/refreshImageView"/>
<Spinner
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/spinner"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:layout_above="@+id/progressBar"
android:entries="@array/country_arrays"
/>
</RelativeLayout>
Spinner spinner = (Spinner) findViewById(R.id.spinner);
在setContentView()之后之前，切勿调用findViewById()。在setContentView()调用之后，将初始化移动到onCreate()方法中。
@InjectView(R.id.textView) TextView mTextView;
@InjectView(R.id.locationLabel) TextView mTimeZone;
@InjectView(R.id.spinner) Spinner spinner;
double latitude = 31.956578300000000000;
double longitude = 35.945695099999966000;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ButterKnife.inject(this);
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(
this,
R.array.Country_array,
android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(adapter);
mProgressBar.setVisibility(View.INVISIBLE);
您需要小心调用setContentView（）和Butterknife.inject（）的顺序。