Question

我是编程新手，遇到一个我自己无法解决的问题。我想要做的是在MainActivity中向ListView填充/添加一些东西，并将其放入SECOND Activity中的EditText中。每次我单击活动2上的按钮时，我的应用程序都会停止工作。我不知道我做错了什么，所以非常感谢帮助。我会发布我的代码：

MainActivity：

public class MainActivity extends AppCompatActivity {

EditText et;
ListView lv;
ArrayList<String> arrayList;
ArrayAdapter<String> adapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    et = (EditText) findViewById(R.id.et);
    lv = (ListView) findViewById(R.id.lv);

    arrayList = new ArrayList<String>();
    adapter = new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_expandable_list_item_1, arrayList);
    lv.setAdapter(adapter);



    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            Intent intent1 = new Intent(MainActivity.this , Activity_2.class);
            startActivityForResult(intent1, 1);//Throws me into Act2
        }
    });
}


public void onActivityResult(int requestCode, int resultCode, Intent intentback){
    super.onActivityResult(requestCode, resultCode, intentback);
    if ( requestCode == 1){
        if(resultCode == RESULT_OK){
            String resultback = intentback.getStringExtra("nameEvent");
            arrayList.add(intentback.getStringExtra("nameEvent"));
            adapter.notifyDataSetChanged();
        }
    }
}

}

想把我扔进Activity_2，输入一个名字：

public class Activity_2 extends AppCompatActivity {

EditText etact;
Button addbtn;
String eventname;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_2_layout);

    addbtn = (Button) findViewById(R.id.addbtn);
    etact = (EditText) findViewById(R.id.etact);
    if ( etact.getText().toString()!= ""){
         eventname = etact.getText().toString();
    }

    addbtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if (eventname == ""){
                Toast.makeText(Activity_2.this,
                        "Make Input first", Toast.LENGTH_LONG).show();
            }
            else {
                Intent intentback = new Intent(Activity_2.this, MainActivity.class);
                intentback.putExtra("nameEvent", eventname);
                setResult(RESULT_OK);
                finish();
            }
        }
    });

}


}

编辑：Logcat

致命的例外：主程序：com.example.robert.againagainagaian， PID：3857 java.lang.RuntimeException：传递结果失败 ResultInfo {who = null，request = 1，result = -1，data = null}到activity {com.example.robert.againagainagaian / com.example.robert.againagainagaian.MainActivity}： java.lang.NullPointerException：尝试调用虚方法 “java.lang.String中 android.content.Intent.getStringExtra（java.lang.String）'为null 对象参考 android.app.ActivityThread.deliverResults（ActivityThread.java:4053）at android.app.ActivityThread.handleSendResult（ActivityThread.java:4096）在android.app.ActivityThread.-wrap20（ActivityThread.java）处 android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1516）在android.os.Handler.dispatchMessage（Handler.java:102）at android.os.Looper.loop（Looper.java:154）at android.app.ActivityThread.main（ActivityThread.java:6077）at java.lang.reflect.Method.invoke（Native Method）at com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:866）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:756）引起 by：java.lang.NullPointerException：尝试调用虚方法 “java.lang.String中 android.content.Intent.getStringExtra（java.lang.String）'为null 对象参考 com.example.robert.againagainagaian.MainActivity.onActivityResult（MainActivity.java:55）在android.app.Activity.dispatchActivityResult（Activity.java:6915）at android.app.ActivityThread.deliverResults（ActivityThread.java:4049）at android.app.ActivityThread.handleSendResult（ActivityThread.java:4096）在android.app.ActivityThread.-wrap20（ActivityThread.java）处 android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1516）在android.os.Handler.dispatchMessage（Handler.java:102）at android.os.Looper.loop（Looper.java:154）at android.app.ActivityThread.main（ActivityThread.java:6077）at java.lang.reflect.Method.invoke（Native Method）at com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:866）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:756）

Answer 1

从intent onActivityResult

访问数据时检查null

  public void onActivityResult(int requestCode, int resultCode, Intent intentback){
            super.onActivityResult(requestCode, resultCode, intentback);
            if ( requestCode == 1){
                if(resultCode == RESULT_OK && intentback.getData()!=null){
                    String resultback = intentback.getStringExtra("nameEvent");
                    arrayList.add(intentback.getStringExtra("nameEvent"));
                    adapter.notifyDataSetChanged();
                }
            }
        }

在SecondActivity上设置结果像这样

if (!("").equals(etact.getText().toString())){
         eventname = etact.getText().toString();
    }

    addbtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if (("").equals(eventname)){
                Toast.makeText(Activity_2.this,
                        "Make Input first", Toast.LENGTH_LONG).show();
            }

            else {
                Intent intentback = new Intent();
                intentback.putExtra("nameEvent", eventname);
                setResult(RESULT_OK, intent);
                finish();
            }

ListView with Button和setResult

1 个答案: