java - 在 Activity 之间传递变量值

Question

我试图在按下按钮时将数字从 activity1 中的 EditText 框传递到 activity2，然后我希望在 activity2 中按下操作栏按钮时该数字显示在 toast 或对话框中。我已经设置了一个 Intent 并编码了我认为应该工作的内容，但它似乎每次都在崩溃 activity2。我放入了应该获取变量的代码行。希望有人能够看到我哪里出错了。我知道在变量中传递数据应该是一项相当容易的任务。
如有任何帮助，我们将不胜感激。

Activity1:

public class activity1 extends Activity {


@Override
protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);
//this.requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.screen_settings);
this.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);

final EditText inputTxt1 = (EditText) findViewById(R.id.conPhoneNum);    
Button saveBtn1 = (Button) findViewById(R.id.btnSave1);


  saveBtn1.setOnClickListener(new View.OnClickListener() {
       @Override
       public void onClick(View view) {
          String phoneNum1 = inputTxt1.getText().toString();
          savenum1(phoneNum1);

  Intent passIntent = new Intent();
  passIntent.putExtra("phoneNum", phoneNum1);

    }
    });
}


public void savenum1(String phoneNum1) {

AlertDialog.Builder dlgAlert  = new AlertDialog.Builder(this);

dlgAlert.setMessage("Saved " + phoneNum1);
dlgAlert.setPositiveButton("OK", null);
dlgAlert.setCancelable(true);

dlgAlert.setPositiveButton("Ok",
    new DialogInterface.OnClickListener() {
    public void onClick(DialogInterface dialog, int which) {
          //dismiss the dialog  
        }
    });    
dlgAlert.create().show();
}
}

Activity 2:

public class Activity2 extends Activity {

      //This is the line that stops the activity from running
String conPhoneNum = getIntent().getExtras().getString("phoneNum");


@SuppressLint("CutPasteId")
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//this.requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.activity_main);

ActionBar actionBar = getActionBar();
actionBar.hide();
actionBar.show();
actionBar.setCustomView(R.layout.actionbar_custom_view_home);
actionBar.setDisplayShowCustomEnabled(true);
actionBar.setDisplayShowHomeEnabled(false);
 }


public boolean onCreateOptionsMenu1(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.main, menu);
    return true;
}





@Override  public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
    case R.id.menu_load:
     Toast toast= Toast.makeText(this, conPhoneNumber, Toast.LENGTH_SHORT);
      toast.setGravity(Gravity.CENTER, 0, -100);
          toast.show();
      break;

         default:
             break;
             }
    return true;
    } 
 }

LogCat 信息:

07-31 15:51:50.135: E/AndroidRuntime(779): FATAL EXCEPTION: main
07-31 15:51:50.135: E/AndroidRuntime(779): java.lang.RuntimeException: Unable to start activity     ComponentInfo{com.cam.data /com.cam.data.Activity2}: java.lang.NullPointerException
 07-31 15:51:50.135: E/AndroidRuntime(779):     at     android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
 07-31 15:51:50.135: E/AndroidRuntime(779):     at     android.app.ActivityThread.handleLaunchActivity     (ActivityThread.java:2135)
 07-31 15:51:50.135: E/AndroidRuntime(779):     at android.app.ActivityThread.access$700    (ActivityThread.java:140)
 07-31 15:51:50.135: E/AndroidRuntime(779):     at android.app.ActivityThread$H.handleMessage     (ActivityThread.java:1237)
 07-31 15:51:50.135: E/AndroidRuntime(779):     at android.os.Handler.dispatchMessage     (Handler.java:99)
07-31 15:51:50.135: E/AndroidRuntime(779):  at android.os.Looper.loop(Looper.java:137)
 07-31 15:51:50.135: E/AndroidRuntime(779):     at android.app.ActivityThread.main    (ActivityThread.java:4921)
 07-31 15:51:50.135: E/AndroidRuntime(779):     at java.lang.reflect.Method.invokeNative(Native Method)
07-31 15:51:50.135: E/AndroidRuntime(779):  at java.lang.reflect.Method.invoke(Method.java:511)
 07-31 15:51:50.135: E/AndroidRuntime(779):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
07-31 15:51:50.135: E/AndroidRuntime(779):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)
07-31 15:51:50.135: E/AndroidRuntime(779):  at dalvik.system.NativeStart.main(Native Method)
07-31 15:51:50.135: E/AndroidRuntime(779): Caused by: java.lang.NullPointerException
07-31 15:51:50.135: E/AndroidRuntime(779):  at com.cam.data.Activity2.onCreate(Activity2.java:66)
 07-31 15:51:50.135: E/AndroidRuntime(779):     at android.app.Activity.performCreate(Activity.java:5206)
07-31 15:51:50.135: E/AndroidRuntime(779):  at     android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
07-31 15:51:50.135: E/AndroidRuntime(779):  at      android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2074)

更新 1: conPhoneNum = getIntent().getExtras().getString("phoneNum"); 仍在使 Activity 崩溃。我发现如果我删除 .getExtras() 那么它不会崩溃，但它也不会显示数据。我不知道这是否是导致应用程序崩溃的任何指标？也许有人可以帮忙

更新 2:
只是对此的更新，我最终放弃了它，只使用在全局类中定义的全局变量，任何 Activity 都可以随时使用。这似乎是一种更好的做这种事情的方法，除非你当然需要传递变量。
显然，如果有人能弄清楚为什么它不起作用，那就太好了，以防其他人遇到这个问题

Answer 1

替换这个

  Intent passIntent = new Intent();
  passIntent.putExtra("phoneNum", phoneNum1);  

通过

  Intent passIntent = new Intent(Activity1.this,Activity2.class);
  passIntent.putExtra("phoneNum", phoneNum1);
  startActivity(passIntent);

进入Activity2:

声明conPhoneNum为类成员

  String conPhoneNum ;

在onCreate中

  conPhnoneNum = getIntent().getExtras().getString("phoneNum");

然后

  Toast toast= Toast.makeText(this, conPhoneNumber, Toast.LENGTH_SHORT);