我传递的包裹是空的？

Question

我不确定如何正确构建这个地块；当我尝试从我的MainActivity 添加包裹的对象时，我将返回null。

发送intent:

public void onClick(View v) {
            Intent myIntent = new Intent(listaddactivity.this,
                    MainActivity.class);

            myIntent.putExtra(
                    "custom_object",
                    new listControlObject(namefield.getText().toString(),
                            iterator, temperatureFrag.getCurrentTempType(), Integer
                                    .valueOf(powerPercent.getText()
                                            .toString()), Integer
                                    .valueOf(frequencyField.getText()
                                            .toString()),
                            temperatureFrag.temperaturenumberpicker
                                    .getValue(), cycleFrag.startTimeField
                                    .getCurrentHour(),
                            cycleFrag.startTimeField.getCurrentMinute(),
                            cycleFrag.cycleDatePicker.getDayOfMonth(),
                            cycleFrag.cycleDatePicker.getMonth(), Integer
                                    .valueOf(cycleFrag.numberOfCyclesField
                                            .getText().toString()))); // Optional
                                                                        // parameters
            startActivity(myIntent);
            Log.d("LISTACTIVITY", "Intent successfully passed!");
            iterator++;  
        }

    });
}

接收activity:

 public class MainActivity extends FragmentActivity implements
        ActionBar.TabListener {
    String TAG;


    HomeFragment homeFragment;
    cycleviewfragment cyclefragment;
    SectionsPagerAdapter mSectionsPagerAdapter;

    /**
     * The {@linkCustomViewPager} that will host the section contents.
     */
    CustomViewPager mViewPager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Set up the action bar.
        final ActionBar actionBar = getActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

        homeFragment = new HomeFragment();
        cyclefragment = new cycleviewfragment();
        // Create the adapter that will return a fragment for each of the three
        // primary sections of the app.
        mSectionsPagerAdapter = new SectionsPagerAdapter(
                getSupportFragmentManager());

        // Set up theCustomViewPager with the sections adapter.
        mViewPager = (CustomViewPager) findViewById(R.id.pager);
        mViewPager.setAdapter(mSectionsPagerAdapter);
        mViewPager.setPagingEnabled(false);
        // When swiping between different sections, select the corresponding
        // tab. We can also use ActionBar.Tab#select() to do this if we have
        // a reference to the Tab.
        mViewPager
                .setOnPageChangeListener(new CustomViewPager.SimpleOnPageChangeListener() {
                    @Override
                    public void onPageSelected(int position) {
                        actionBar.setSelectedNavigationItem(position);
                    }
                });

        // For each of the sections in the app, add a tab to the action bar.
        for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {
            // Create a tab with text corresponding to the page title defined by
            // the adapter. Also specify this Activity object, which implements
            // the TabListener interface, as the callback (listener) for when
            // this tab is selected.
            actionBar.addTab(actionBar.newTab()
                    .setText(mSectionsPagerAdapter.getPageTitle(i))
                    .setTabListener(this));
        }
        processNewIntent(getIntent());


    }
    @Override
    protected void onNewIntent(Intent intent) {
        super.onNewIntent(intent);
        processNewIntent(intent);
    }

    private void processNewIntent(Intent intent) {
        Log.v("TEST", "METHOD CALLED TEST");
        if (intent.hasExtra("custom_object")) {
            cyclefragment.a1.add((listControlObject) intent.getParcelableExtra("custom_object"));
            cyclefragment.adapter.notifyDataSetChanged();
        }
    }

我发送intent 时是否错误地执行了包裹？我的processNewIntent 给我NullPointerException 有什么原因吗？

我猜有一种特定的方法可以构造一个包裹并将其传递给我没有正确实现的意图，但我找不到任何好的资源。

Logcat:

   03-24 01:13:30.846: E/Trace(7974): error opening trace file: No such file or directory (2)
03-24 01:13:44.374: E/AndroidRuntime(7974): FATAL EXCEPTION: main
03-24 01:13:44.374: E/AndroidRuntime(7974): java.lang.NullPointerException
03-24 01:13:44.374: E/AndroidRuntime(7974):     at com.nanospark.upcdemo.listaddactivity$1.onClick(listaddactivity.java:72)
03-24 01:13:44.374: E/AndroidRuntime(7974):     at android.view.View.performClick(View.java:4091)
03-24 01:13:44.374: E/AndroidRuntime(7974):     at android.view.View$PerformClick.run(View.java:17072)
03-24 01:13:44.374: E/AndroidRuntime(7974):     at android.os.Handler.handleCallback(Handler.java:615)
03-24 01:13:44.374: E/AndroidRuntime(7974):     at android.os.Handler.dispatchMessage(Handler.java:92)
03-24 01:13:44.374: E/AndroidRuntime(7974):     at android.os.Looper.loop(Looper.java:153)
03-24 01:13:44.374: E/AndroidRuntime(7974):     at android.app.ActivityThread.main(ActivityThread.java:4987)
03-24 01:13:44.374: E/AndroidRuntime(7974):     at java.lang.reflect.Method.invokeNative(Native Method)
03-24 01:13:44.374: E/AndroidRuntime(7974):     at java.lang.reflect.Method.invoke(Method.java:511)
03-24 01:13:44.374: E/AndroidRuntime(7974):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:821)
03-24 01:13:44.374: E/AndroidRuntime(7974):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:584)
03-24 01:13:44.374: E/AndroidRuntime(7974):     at dalvik.system.NativeStart.main(Native Method)

谢谢大家。

编辑：

listaddactivity.java 的第 72 行：

myIntent.putExtra(
                    "custom_object",
                    new listControlObject(namefield.getText().toString(),
                            iterator, temperatureFrag.getCurrentTempType(), Integer
                                    .valueOf(powerPercent.getText()
                                            .toString()), Integer
                                    .valueOf(frequencyField.getText()
                                            .toString()),
                            temperatureFrag.temperaturenumberpicker
                                    .getValue(), cycleFrag.startTimeField
                                    .getCurrentHour(),
                            cycleFrag.startTimeField.getCurrentMinute(),
                            cycleFrag.cycleDatePicker.getDayOfMonth(),
                            cycleFrag.cycleDatePicker.getMonth(), Integer
                                    .valueOf(cycleFrag.numberOfCyclesField
                                            .getText().toString())));

上面只是构造了一个新对象，并将其添加到带有“自定义对象”键的意图中。

这里是parcelable对象的代码：

    package com.nanospark.upcdemo;

import android.os.Parcel;
import android.os.Parcelable;

public class listControlObject implements Parcelable {
    private String name;
    private int id;
    private int tempType;// 0 for fahrenheit, 1 for celsius.
    private int powerPercent;
    private int freq;
    private int temp;
    private int cycleDateDay;
    private int cycleDateMonth;
    private int numberOfCycles;
    private int cycleTimeHour;
    private int cycleTimeMinute;

    public listControlObject(String name, int id, int tempType,
            int powerPercent, int freq, int temp, int cycleTimeHour,
            int cycleTimeMinute, int cycleDateDay, int cycleDateMonth,
            int numberOfCycles) {
        this.id = id;
        this.name = name;
        this.cycleDateDay = cycleDateDay;
        this.cycleDateMonth = cycleDateMonth;
        this.cycleTimeHour = cycleTimeHour;
        this.cycleTimeMinute = cycleTimeMinute;
        this.freq = freq;
        this.numberOfCycles = numberOfCycles;
        this.powerPercent = powerPercent;
        this.temp = temp;
        this.tempType = tempType;

    }

    private listControlObject(Parcel in){
        this.id = in.readInt();
        this.name = in.readString();
        this.cycleDateDay = in.readInt();
        this.cycleDateMonth = in.readInt();
        this.cycleTimeHour = in.readInt();
        this.cycleTimeMinute = in.readInt();
        this.freq = in.readInt();
        this.numberOfCycles = in.readInt();
        this.powerPercent = in.readInt();
        this.temp = in.readInt();
        this.tempType = in.readInt();

    }

    public int getCycleDateDay() {
        return cycleDateDay;
    }

    public void setCycleDateDay(int cycleDateDay) {
        this.cycleDateDay = cycleDateDay;
    }

    public int getCycleDateMonth() {
        return cycleDateMonth;
    }

    public void setCycleDateMonth(int cycleDateMonth) {
        this.cycleDateMonth = cycleDateMonth;
    }

    public int getCycleTimeHour() {
        return cycleTimeHour;
    }

    public void setCycleTimeHour(int cycleTimeHour) {
        this.cycleTimeHour = cycleTimeHour;
    }

    public int getCycleTimeMinute() {
        return cycleTimeMinute;
    }

    public void setCycleTimeMinute(int cycleTimeMinute) {
        this.cycleTimeMinute = cycleTimeMinute;
    }

    public int getNumberOfCycles() {
        return numberOfCycles;
    }

    public void setNumberOfCycles(int numberOfCycles) {
        this.numberOfCycles = numberOfCycles;
    }

    public int getTempType() {
        return tempType;
    }

    public void setTempType(int tempType) {
        this.tempType = tempType;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getPowerPercent() {
        return powerPercent;
    }

    public void setPowerPercent(int powerPercent) {
        this.powerPercent = powerPercent;
    }

    public int getFreq() {
        return freq;
    }

    public void setFreq(int freq) {
        this.freq = freq;
    }

    public int getTemp() {
        return temp;
    }

    public void setTemp(int temp) {
        this.temp = temp;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    @Override
    public String toString() {

        return this.name;
    }

    @Override
    public int describeContents() {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public void writeToParcel(Parcel parcel, int flags) {
        parcel.writeInt(id);
        parcel.writeString(name);
        parcel.writeInt(cycleDateDay);
        parcel.writeInt(cycleDateMonth);
        parcel.writeInt(cycleTimeHour);
        parcel.writeInt(cycleTimeMinute);
        parcel.writeInt(freq);
        parcel.writeInt(numberOfCycles);
        parcel.writeInt(powerPercent);
        parcel.writeInt(temp);
        parcel.writeInt(tempType);

    }
    public static Creator<listControlObject> CREATOR = new Creator<listControlObject>() {
        public listControlObject createFromParcel(Parcel parcel) {
            return new listControlObject(parcel);
        }

        public listControlObject[] newArray(int size) {
            return new listControlObject[size];
        }

    };


}

编辑：

我发现了我的错误来源：

当我需要传递一个listControlObject时，我在这里传递一个包裹。

cyclefragment.a1.add(intent.getParcelableExtra("custom_object"));
            cyclefragment.adapter.notifyDataSetChanged();

如何将intent.getParcelableExtra("custom_object") 转换回listControlObject？

[更新]

新的 Logcat 错误：

    03-24 02:29:46.177: E/AndroidRuntime(9685): FATAL EXCEPTION: main
03-24 02:29:46.177: E/AndroidRuntime(9685): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.nanospark.upcdemo/com.nanospark.upcdemo.MainActivity}: java.lang.NullPointerException
03-24 02:29:46.177: E/AndroidRuntime(9685):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
03-24 02:29:46.177: E/AndroidRuntime(9685):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2211)
03-24 02:29:46.177: E/AndroidRuntime(9685):     at android.app.ActivityThread.access$600(ActivityThread.java:149)
03-24 02:29:46.177: E/AndroidRuntime(9685):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1300)
03-24 02:29:46.177: E/AndroidRuntime(9685):     at android.os.Handler.dispatchMessage(Handler.java:99)
03-24 02:29:46.177: E/AndroidRuntime(9685):     at android.os.Looper.loop(Looper.java:153)
03-24 02:29:46.177: E/AndroidRuntime(9685):     at android.app.ActivityThread.main(ActivityThread.java:4987)
03-24 02:29:46.177: E/AndroidRuntime(9685):     at java.lang.reflect.Method.invokeNative(Native Method)
03-24 02:29:46.177: E/AndroidRuntime(9685):     at java.lang.reflect.Method.invoke(Method.java:511)
03-24 02:29:46.177: E/AndroidRuntime(9685):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:821)
03-24 02:29:46.177: E/AndroidRuntime(9685):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:584)
03-24 02:29:46.177: E/AndroidRuntime(9685):     at dalvik.system.NativeStart.main(Native Method)
03-24 02:29:46.177: E/AndroidRuntime(9685): Caused by: java.lang.NullPointerException
03-24 02:29:46.177: E/AndroidRuntime(9685):     at com.nanospark.upcdemo.MainActivity.processNewIntent(MainActivity.java:88)
03-24 02:29:46.177: E/AndroidRuntime(9685):     at com.nanospark.upcdemo.MainActivity.onCreate(MainActivity.java:70)
03-24 02:29:46.177: E/AndroidRuntime(9685):     at android.app.Activity.performCreate(Activity.java:5020)
03-24 02:29:46.177: E/AndroidRuntime(9685):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
03-24 02:29:46.177: E/AndroidRuntime(9685):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2148)
03-24 02:29:46.177: E/AndroidRuntime(9685):     ... 11 more

相关代码：

@Override
    protected void onNewIntent(Intent intent) {
        super.onNewIntent(intent);
        processNewIntent(intent);
    }

    private void processNewIntent(Intent intent) {
        Log.v("TEST", "METHOD CALLED TEST");
        if (intent.hasExtra("custom_object")) {
            if (intent.getParcelableExtra("custom_object")
                    .equals(null)) {
                Log.v("Testing null", "Object is null");
            } else {
                Log.v("Testing null", "Object is not null");
                cyclefragment.a1.add((listControlObject) intent.getParcelableExtra("custom_object"));
                cyclefragment.adapter.notifyDataSetChanged();
            }
        }
    }

logcat 错误指的是这一行：

cyclefragment.a1.add((listControlObject) intent.getParcelableExtra("custom_object"));

我做了

private listControlObject(Parcel in){

public listControlObject(Parcel in){

根据 cmets 的要求。仍然收到错误。

Answer 1

您的跟踪文件似乎已损坏或被另一个进程保留。 Logcat上线可能报错：Log.d("LISTACTIVITY", "Intent successfully passed!");

或者您检查活动中的所有namefield 或temperatureFrag ...，以确保在调用发送活动的onClick() 之前它们的实例都已初始化。

因为您在一个代码行中调用了所有实例，所以很难找出错误。试试 DDMS 进行调试！

P/S：你的代码中的第 72 行在哪里？

[更新]

更多详情： Passing a custom Object from one Activity to another Parcelable vs Bundle

如果您已经很好地“包裹”了，在您的目标活动中，只需将收到的对象转换为原始类型，就像您在代码中所做的那样。

您的代码错误是private listControlObject(Parcel in) 和private。更改为public，以便 Intent 可以使用此构造函数从先前打包的字符串中恢复对象。