java - Intent Android : click the button text is not transferred and show nothing

Question

我遇到了 Intent 问题。我从 YouTube (thenewboston) 了解到，当我启动应用程序并单击按钮时，文本不会传输，也不显示任何内容。

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


    public void onClick(View view){
        Intent i = new Intent(this,Bacon.class);

        final EditText applesInput = (EditText)findViewById(R.id.applesInput);
        String userMessage = applesInput.getText().toString();
        i.putExtra("appleMessage",userMessage);

        startActivity(i);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_apples, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

XML 布局:

    <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=".Apples"
    android:background="#009900">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Go to bacon"
        android:id="@+id/applesButton"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true"
        android:onClick="onClick"/>

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/applesInput"
        android:layout_above="@+id/applesButton"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="41dp"
        android:width="250dp" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Large Text"
        android:id="@+id/applesText"
        android:layout_above="@+id/applesInput"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="41dp" />
</RelativeLayout>






 <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="New Text"
        android:id="@+id/textView"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="198dp" />
</RelativeLayout>

培根 Activity :

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

    Bundle applesData =getIntent().getExtras();
    if(applesData==null){
        return;
    }
    String appleMessage = applesData.getString("applesMessage");
    final TextView textView=(TextView)findViewById(R.id.textView);
    textView.setText(appleMessage);
}

Answer 1

您的额外键名不匹配。您将数据作为 appleMessage 放入，但将其作为 applesMessage 检索，这将返回 null。

为了确保将来不会发生这种情况，您应该在接收 Intent 的类中定义一个静态最终常量。

public static final String EXTRA_APPLE_MSG = "appleMessage";

您的源 Activity 将使用它作为

    String userMessage = applesInput.getText().toString();
    i.putExtra(Bacon.EXTRA_APPLE_MSG,userMessage);