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Question

我正在Android Studio中学习Android开发。 我创建了一个应用程序，在点击按钮时显示一些文本和其他一些文本。 但它显示“遗憾的应用已停止” 另外，我只有一项活动。所以，我不可能忘记在AndroidManifest.xml中显示它 这是我的java代码：

package com.example.mahe.pro2;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
import android.widget.Button;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.View;
import android.support.v4.view.GestureDetectorCompat;

public class MainActivity extends AppCompatActivity implements    GestureDetector.OnGestureListener {

private TextView tv = (TextView) findViewById(R.id.t);
private GestureDetectorCompat gd;
private Button bt = (Button) findViewById(R.id.b);

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    this.gd = new GestureDetectorCompat(this,this);

    bt.setOnClickListener(
            new Button.OnClickListener() {
                public void onClick(View v) {
                    tv.setText("That was a Click!");
                }
            }
    );
}

@Override
public void onLongPress(MotionEvent motionEvent) {
}

@Override
public boolean onSingleTapUp(MotionEvent motionEvent) {
    return false;
}

@Override
public boolean onScroll(MotionEvent motionEvent, MotionEvent motionEvent1, float v, float v1) {
    return false;
}

@Override
public void onShowPress(MotionEvent motionEvent) {

}

@Override
public boolean onDown(MotionEvent motionEvent) {
    return false;
}

@Override
public boolean onFling(MotionEvent motionEvent, MotionEvent motionEvent1, float v, float v1) {
    tv.setText("That was a Swipe, Baby");
    return true;
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    this.gd.onTouchEvent(event);
    return super.onTouchEvent(event);
}

@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_main, 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);
}

}

这是我的xml代码：

    <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=".MainActivity">

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceLarge"
    android:text="YO!"
    android:id="@+id/t"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="62dp" />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Click"
    android:id="@+id/b"
    android:layout_below="@+id/t"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="164dp" />

Answer 1

移动

apply

在t(apply(df, 1, function(x) { w <- na.omit(which(is.na(x))[1:3]) x[w] <- list1[1:length(w)] x }))

之后的TextView tv = (TextView) findViewById(R.id.t); Button bt = (Button) findViewById(R.id.b); 下

Answer 2

正如@M D所说 你必须首先创建你的视图和setview才能获得R.id.b

但是如果要将它们声明为全局变量，请使用

private TextView tv;
private Button bt

在onCreate方法之上，然后在onCreate方法中，在

之下

的setContentView（R.layout.activity_main）;

使用

tv = (TextView) findViewById(R.id.t);
bt = (Button) findViewById(R.id.b);