Question

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.v_krkoru.androidapp.MainActivity">

    <EditText
        android:id="@+id/editText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="16dp"
        android:ems="10"
        android:inputType="textPersonName"
        android:text="@string/message_text"
        app:layout_constraintRight_toLeftOf="@+id/button"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:layout_marginTop="16dp" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="sendMessage"
        android:text="@string/button_send"
        app:layout_constraintBaseline_toBaselineOf="@+id/editText"
        app:layout_constraintLeft_toRightOf="@+id/editText"
        app:layout_constraintRight_toRightOf="parent" />
</android.support.constraint.ConstraintLayout>

package com.example.v_krkoru.androidapp;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {

    public static final String EXTRA_MESSAGE = "com.example.androidapp.MESSAGE";

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

    public void sendMessage(View view)
    {
        Intent intent  = new Intent(this, DisplayMessageActivity.class);
        EditText editText = (EditText) findViewById(R.id.editText);
        String message = editText.getText().toString();
        intent.putExtra(EXTRA_MESSAGE, message);
        startActivity(intent);
    }
}

package com.example.v_krkoru.androidapp;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.TextView;
import android.view.ViewGroup;

public class DisplayMessageActivity extends AppCompatActivity {

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

    Intent intent = getIntent();
    String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);

    TextView textView = (TextView) findViewById(R.id.textView);
    textView.setText(message);

}

这里我输入了两个活动的java代码，这些活动是通过意图相互关联的，当我输入一条消息并点击发送按钮时，我想要做的是下一个活动应该显示在新屏幕上键入的消息我从android网站上学习这个并且因为setText（）方法不能正常工作。现在添加了xml代码以供那些愿意回答的人参考

Answer 1

//你已经在onCreate方法之外编写了findViewById（）。

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_display_message);
    TextView textView = (TextView) findViewById(R.id.textView); // this line should be inside your onCreate method.
}

Answer 2

此代码在我这方面运作良好。

public class DisplayMessageActivity extends AppCompatActivity {
    private TextView mTextview;
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.acivity_demo);
        Intent intent = getIntent();
        String message = intent.getStringExtra(MainActivity.EXTRA_MESSAGE);

       mTextview = (TextView) findViewById(R.id.textView);
        mTextview.setText(message);

    }
}

基本应用程序setText（）不起作用

2 个答案: