设置LayoutParams时出现NullPointerException [英] NullPointerException while setting LayoutParams

问题描述

我想以编程方式添加一个按钮，也应该设置LayoutParams。
不幸的是，该应用程序给出了一个例外：

I want to add a button programmatically, which LayoutParams should be set too. Unfortunaly the app gives an exception:

java.lang.NullPointerException：尝试写入字段'int
在null对象引用上的android.view.ViewGroup $ LayoutParams.height'

java.lang.NullPointerException: Attempt to write to field 'int android.view.ViewGroup$LayoutParams.height' on a null object reference

我不知道，为什么。你可以帮帮我吗？
这是我的代码。

I have no idea, why. Could you help me? Here is my code.

 Button b = new Button(getApplicationContext());
        b.setText(R.string.klick);
        ViewGroup.LayoutParams params = b.getLayoutParams();
        params.height = ViewGroup.LayoutParams.MATCH_PARENT;
        params.height = ViewGroup.LayoutParams.WRAP_CONTENT;

推荐答案

由于您是以编程方式创建Button b 将不会设置任何布局参数。所以你需要像这样手动设置它们：

Since you are creating a Button programmatically b will not have any layout params set. So you'll need to set them manually like this:

ViewGroup.LayoutParams params = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT);
b.setLayoutParams(params);

或至少在更改之前检查params是否为空

Or at least check if params are not null before changing them

    ViewGroup.LayoutParams params = b.getLayoutParams();
    if (params != null) {
        params.width= ViewGroup.LayoutParams.MATCH_PARENT;
        params.height = ViewGroup.LayoutParams.WRAP_CONTENT;
    } else
        params = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT);

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