我正在构建一个Android应用程序，在主要布局上我有3个图像按钮，点击它们时每个都必须打开一个新的活动。
当我运行应用程序并按下它们时，应用程序会崩溃。这是我正在使用的代码：
MainActivity.java
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ImageButton converterbtn = (ImageButton)findViewById(R.id.btnConvert);
ImageButton placesbtn = (ImageButton)findViewById(R.id.imagBtnPlace);
ImageButton weatherbtn = (ImageButton)findViewById(R.id.imgbtnweather);
//Open Weather Activity
if (weatherbtn.isPressed() == true) {
weatherbtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
Intent intent = new Intent(getApplicationContext(), weather_mainActivity.class);
startActivity(intent);
}
}); //Open Currency Activity
}else if (converterbtn.isPressed() == true) {
converterbtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
Intent intent1 = new Intent(getApplicationContext(), CurrencyConverter_MainActivity.class);
startActivity(intent1);
}
});//Open Places Activity
} else if (placesbtn.isPressed()) {
placesbtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
Intent intent1 = new Intent(getApplicationContext(), Places_mainActivity.class);
startActivity(intent1);
}
});
}
}
的Manifest.xml
<activity android:name=".CurrencyConverter_MainActivity"/>
<activity android:name=".weather_mainActivity"/>
为什么会这样？ 我检查过的所有其他帖子都是这样做的，但在我看来它似乎不起作用。
Android监视器日志
01-08 03:00:58.288 22447-22447/? D/AndroidRuntime: Shutting down VM
--------- beginning of crash
01-08 03:01:01.127 1236-1547/? D/AudioFlinger: mixer(0xf4480000) throttle end: throttle time(56)
01-08 03:01:01.151 1550-21914/? D/OpenGLRenderer: endAllStagingAnimators on 0x7f0b1b83d400 (RippleDrawable) with handle 0x7f0b1b8bb540
01-08 03:01:01.192 1550-1954/? D/GraphicsStats: Buffer count: 3
Weather_MainActivity.java
package com.android.example.cwapp;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.graphics.drawable.Drawable;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;
import android.provider.Settings;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.ImageView;
import android.widget.ProgressBar;
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 weather_mainActivity extends AppCompatActivity {
public static final String TAG = weather_mainActivity.class.getSimpleName();
private CurrentWeather mCurrentWeather;
LocationManager locationManager;
@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.summaryLabel)TextView mSummaryLabel;
@InjectView(R.id.iconImageView)ImageView mIconImageView;
@InjectView(R.id.refreshImageView)ImageView mRefreshImageView;
@InjectView(R.id.progressBar)ProgressBar mProgressBar;
@InjectView(R.id.locationLabel)TextView mLocation;
public double latitude /*= 34.7720*/;
public double longitude /*= 32.4297*/;
//Location Manager
private boolean checkLocation() {
if (!isLocationEnabled())
showAlert();
return isLocationEnabled();
}
private void showAlert() {
final AlertDialog.Builder dialog = new AlertDialog.Builder(this);
dialog.setTitle("Enable Location")
.setMessage("Your Locations Settings is set to 'Off'.\nPlease Enable Location to " +
"use this app")
.setPositiveButton("Location Settings", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface paramDialogInterface, int paramInt) {
Intent myIntent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
startActivity(myIntent);
}
})
.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface paramDialogInterface, int paramInt) {
}
});
dialog.show();
}
private boolean isLocationEnabled() {
return locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER) ||
locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
}
private final LocationListener locationListenerBest = new LocationListener() {
public void onLocationChanged(Location location) {
longitude = location.getLongitude();
latitude = location.getLatitude();
}
@Override
public void onStatusChanged(String s, int i, Bundle bundle) {
}
@Override
public void onProviderEnabled(String s) {
}
@Override
public void onProviderDisabled(String s) {
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
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 code is running!");
}
private void getForecast(double latitude, double longitude) {
String apiKey = "6180f6e1b6747c1da3cb4638ea9d2961";
String forecastUrl = "https://api.forecast.io/forecast/" + apiKey +
"/" + latitude + "," + longitude;
if (isNetworkAvailable()) {
toggleRefresh();
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_message),
Toast.LENGTH_LONG).show();
}
}
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 updateDisplay() {
float temp = mCurrentWeather.getTemperature();
String temp2 = Float.toString((temp - 32) * (5 / 9));
mTemperatureLabel.setText(temp2 + "");
mTimeLabel.setText("At " + mCurrentWeather.getFormattedTime() + " it will be");
mHumidityValue.setText(mCurrentWeather.getHumidity() + "");
mPrecipValue.setText(mCurrentWeather.getPrecipChance() + "%");
mSummaryLabel.setText(mCurrentWeather.getSummary());
mLocation.setText(mCurrentWeather.getTimeZone());
Drawable drawable = getResources().getDrawable(mCurrentWeather.getIconId());
mIconImageView.setImageDrawable(drawable);
}
private CurrentWeather getCurrentDetails(String jsonData) throws JSONException {
JSONObject forecast = new JSONObject(jsonData);
String timezone = forecast.getString("timezone");
Log.i(TAG, "From JSON: " + timezone);
JSONObject currently = forecast.getJSONObject("currently");
CurrentWeather currentWeather = new CurrentWeather();
currentWeather.setHumidity(currently.getDouble("humidity"));
currentWeather.setTime(currently.getLong("time"));
currentWeather.setIcon(currently.getString("icon"));
currentWeather.setPrecipChance(currently.getDouble("precipProbability"));
currentWeather.setSummary(currently.getString("summary"));
currentWeather.setTemperature(currently.getDouble("temperature"));
currentWeather.setTimeZone(timezone);
Log.d(TAG, currentWeather.getFormattedTime());
return currentWeather;
}
private boolean isNetworkAvailable() {
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 alertUserAboutError() {
AlertDialogFragment_weather dialog = new AlertDialogFragment_weather();
dialog.show(getFragmentManager(), "error_dialog");
}
};
运行日志
01-09 21:29:30.827 5610-5610/? E/memtrack: Couldn't load memtrack module (No such file or directory)
01-09 21:29:30.827 5610-5610/? E/android.os.Debug: failed to load memtrack module: -2
01-09 21:29:30.864 5610-5627/? E/art: Thread attaching while runtime is shutting down: Binder_2
01-09 21:29:30.869 5614-5614/? E/memtrack: Couldn't load memtrack module (No such file or directory)
01-09 21:29:30.870 5614-5614/? E/android.os.Debug: failed to load memtrack module: -2
01-09 21:29:30.916 1548-1596/? E/InputDispatcher: channel '6ba3a14 com.android.example.cwapp/com.android.example.cwapp.MainActivity (server)' ~ Channel is unrecoverably broken and will be disposed!
01-09 21:29:31.830 5633-5633/? E/memtrack: Couldn't load memtrack module (No such file or directory)
01-09 21:29:31.830 5633-5633/? E/android.os.Debug: failed to load memtrack module: -2
01-09 21:29:32.033 1195-1309/? E/SurfaceFlinger: ro.sf.lcd_density must be defined as a build property
01-09 21:29:33.170 1921-2145/? E/Surface: getSlotFromBufferLocked: unknown buffer: 0xedc344f0
01-09 21:30:01.551 5641-5654/? E/Surface: getSlotFromBufferLocked: unknown buffer: 0x7f44b819a240
01-09 21:30:02.902 5641-5654/? E/Surface: getSlotFromBufferLocked: unknown buffer: 0x7f44b1cf8310
01-09 21:30:04.739 5641-5654/? E/Surface: getSlotFromBufferLocked: unknown buffer: 0x7f44b819b580
01-09 21:30:06.655 5641-5654/? E/Surface: getSlotFromBufferLocked: unknown buffer: 0x7f44b1cf8380
01-09 21:30:08.253 5641-5654/? E/Surface: getSlotFromBufferLocked: unknown buffer: 0x7f44b1bed700
01-09 21:30:09.115 5641-5641/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.android.example.cwapp, PID: 5641
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.android.example.cwapp/com.android.example.cwapp.Places_mainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at com.android.example.cwapp.Places_mainActivity.onCreate(Places_mainActivity.java:36)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
01-09 21:30:11.307 1548-1601/? E/Surface: getSlotFromBufferLocked: unknown buffer: 0x7f44b1c8f020
01-09 21:30:11.326 1548-1937/? E/JavaBinder: !!! FAILED BINDER TRANSACTION !!! (parcel size = 104)
答案 0 :(得分：0)
在此主要节日中添加CurrentWeather.class个活动
<activity android:name=".CurrencyConverter_MainActivity"/>
<activity android:name=".weather_mainActivity"/>
<activity android:name=".CurrentWeather"/>
答案 1 :(得分：0)
您应该显示堆栈跟踪，但是您不需要View.OnClickListner，不确定是否会导致它，但只有weatherbtn.setOnClickListener（new OnClickListener（）{...
除此之外，您如何调用自己的活动并没有任何问题。