每当我创建一个新的按钮，我的应用程序强制关闭 [英] Whenever I create a new button my app force closes

问题描述

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup.LayoutParams;
import android.widget.Button;
import android.widget.RelativeLayout;

public class register_activity extends Activity {


@Override
public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.register);

        RelativeLayout RLayout = (RelativeLayout) View.inflate(this, R.layout.register, null);

        RelativeLayout.LayoutParams p = new RelativeLayout.LayoutParams(
                RelativeLayout.LayoutParams.FILL_PARENT,
                RelativeLayout.LayoutParams.WRAP_CONTENT
        );

        Button btnCreateNew = new Button(this);
        btnCreateNew.setText("Create New User");
        btnCreateNew.offsetTopAndBottom(10);
        btnCreateNew.offsetLeftAndRight(10);
        RLayout.addView(btnCreateNew, p);

    }
}

这样code ++工程，并运行得很好，只是我看不到显示的按钮。布局是简单地里面什么都没有空白。

So that code works and runs just fine, only I can not see the button being displayed. The layout is simply blank with nothing inside it.

什么是错的？

推荐答案

您有一个NullPointerException异常，对不对？ （检查你的LogCat中！）

You got a NullPointerException, right? (Check your LogCat!)

究其原因：

1. 您创建一个Button与这个作为参数的成员变量。这可能会导致一些麻烦的，因为这个在新按钮（这个）被称为可能无法确定。移动初始化成的onCreate

1. You create a Button as a member variable with this as a parameter. That might cause some trouble as this might not be defined when new Button(this) is called. Move the initialization into onCreate

您 RLayout 将是空的，在这里我非常肯定。其原因是，你不能叫 findViewById（）你调用之前的setContentView（）。如果你之前调用它，Android有不知道从哪里看，并返回null。

Your RLayout will be null, and here I am very sure. The reason is, that you can't call findViewById() before you called setContentView(). If you call it before, Android has no idea where to look at and returns null.

的更新的

当你改变了你的问题相当多，这是我更新的答案：

As you changed your question quite a bit, here is my updated answer:

您设置你的内容 R.layout.register ，之后您再次膨胀了。

You set your content to R.layout.register and after that you inflate it again.

我对你的解决方案：只需使用的setContentView（R.layout.register），不是使用 findViewById（R.id.layout_id）并最终创建并添加按钮：

My solution for you: just use setContentView(R.layout.register), than use findViewById(R.id.layout_id) and finally create and add your button:

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.register);

    RelativeLayout RLayout = (RelativeLayout) findViewById(R.id.layout_id);

    RelativeLayout.LayoutParams p = new RelativeLayout.LayoutParams(
            RelativeLayout.LayoutParams.FILL_PARENT,
            RelativeLayout.LayoutParams.WRAP_CONTENT
    );

    Button btnCreateNew = new Button(this);
    btnCreateNew.setText("Create New User");
    btnCreateNew.offsetTopAndBottom(10);
    btnCreateNew.offsetLeftAndRight(10);
    RLayout.addView(btnCreateNew, p);
}

当然，你也可以在XML布局直接添加按钮。我想preFER这种方式，因为你的布局和code之间较好的分离。

Of course you can also add the button in the xml layout directly. I would prefer this way, because you have a better separation between layout and code.

基本的XML结构（它的风格，只要你想）：

Basic XML structure (style it to as you want):

<RelativeLayout android:id="@+id/layout_id"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >
    <Button android:id="@+id/button_id"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:text="@string/button_text"/>
</RelativeLayout>

的理由让你黑屏了，您添加的按钮，将新创建 RLayout ，但这种布局是从来没有你的屏幕（从未被<$ C补充的一部分$ C>的setContentView（））

The reason for you blank screen was, that you added the button to the new created RLayout but this layout was never part of your screen (never added by setContentView())

这篇关于每当我创建一个新的按钮，我的应用程序强制关闭的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！