Set LayoutParams on parentless LinearLayout

问题

I creating LinearLayout programatically then I want to attach it to GridView via custom written adapter. I want to set width and height to my newly created LinearLayout. When I try to do so I get following exception:

03-18 15:50:54.648: E/AndroidRuntime(2708): java.lang.ClassCastException: android.widget.LinearLayout$LayoutParams
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.widget.GridView.onMeasure(GridView.java:937)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.view.View.measure(View.java:8313)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1017)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.widget.LinearLayout.measureVertical(LinearLayout.java:386)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:309)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.view.View.measure(View.java:8313)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:250)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.view.View.measure(View.java:8313)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.widget.LinearLayout.measureVertical(LinearLayout.java:531)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:309)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.view.View.measure(View.java:8313)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:250)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.view.View.measure(View.java:8313)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.view.ViewRoot.performTraversals(ViewRoot.java:839)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1859)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.os.Handler.dispatchMessage(Handler.java:99)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.os.Looper.loop(Looper.java:130)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at android.app.ActivityThread.main(ActivityThread.java:3683)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at java.lang.reflect.Method.invokeNative(Native Method)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at java.lang.reflect.Method.invoke(Method.java:507)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
03-18 15:50:54.648: E/AndroidRuntime(2708):     at dalvik.system.NativeStart.main(Native Method)

Here is my code:

public View getView(int position, View convertView, ViewGroup parent){
  LinearLayout layout = new LinearLayout(activity);

  LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(100, 100);
  layout.setLayoutParams(params);

  return layout
}

Any help will be appreciated.

回答1:

Try it with GridView.LayoutParams. The LayoutParams have to be the params of the parent.

public View getView(int position, View convertView, ViewGroup parent){
  LinearLayout layout = new LinearLayout(activity);
  layout.setLayoutParams(new GridView.LayoutParams(100, 100));
  return layout
}

btw the convertView should be used if it is != null. That's faster.

public View getView(int position, View convertView, ViewGroup parent){
  View result = convertView;
  if (result == null) {
      result = new LinearLayout(activity);
      result.setLayoutParams(new GridView.LayoutParams(100, 100));
  }
  // set attributes based on position here
  return result;
}

Edit:

// using ViewGroup
public View getView(int position, View convertView, ViewGroup parent){
  ViewGroup result = null;
  if (convertView instanceof ViewGroup) {
      result = (ViewGroup) convertView;
  } else {
     // that will never happen if you never return anything but ViewGroups
  }

  if (result == null) {
      // since LinearLayout is a (extends) ViewGroup
      result = new LinearLayout(activity);
      result.setLayoutParams(new GridView.LayoutParams(100, 100));
  }
  // set attributes based on position here
  return result;
}

回答2:

LayoutParams is relative to the parent.

AbsListView.LayoutParams params = new AbsListView.LayoutParams(100,100);
layout.setLayoutParams(params);

来源：https://stackoverflow.com/questions/9758078/set-layoutparams-on-parentless-linearlayout

标签

android

android-layout

layoutparams